Is an Engine Flush Good or Bad?

Let’s get right to the point: Is an engine flush good or bad?

Spend a few minutes perusing online forums and you’ll find a range of answers to this question, often involving an old Trans-Am, Camaro or other car that someone thrashed on for years, parked in a pasture for a decade and now wants to revive with an engine flush.

Here’s what we’ll cover:

What is an engine flush?

An engine flush is an aftermarket chemical additive designed to clean accumulated deposits, sludge and other gunk from your engine.

You pour it into your engine’s oil-filler port and idle the engine for about 10-15 minutes. It mixes with the oil and circulates through the engine, helping dissolve sludge and clean deposits.

Then, you drain the oil (along with much of the gunk, in theory), change the oil filter, add fresh oil and return to the business of driving.

How deposits and sludge form inside an engine

If it did its job, your engine’s performance will return to the heady days of its youth, when it delivered maximum power and efficiency.

Over time, however, harmful deposits and sludge may have accumulated, causing power and performance loss.

Deposits and sludge can form for several reasons, including…

  • Frequent short trips that don’t allow the oil to fully warm up and evaporate moisture
  • Ingestion of dirt
  • Fuel dilution
  • High heat breaking down the oil

As it settles, sludge can clog narrow oil passages or the screen on the oil pickup tube, restricting oil flow to vital parts, especially the upper valve train.

Deposits can cause the rings to stick, reducing engine compression and horsepower.

Engine Flush - clogged oil pickup tube screen
The tiny openings in the oil pickup tube screen can easily plug with sludge, starving the engine of oil.

Can engine sludge be removed?

Yes. The proper detergents in the correct concentration can dissolve engine sludge, deposits and varnish.

Ideally, sludge won’t form at all; however, sometimes mechanical issues arise, such as a leaking head gasket, and the formation of sludge occurs.

If sludge does form, the oil’s detergents help dissolve and disperse sludge to clean the engine.

Clean engine sludge

This is more challenging than it sounds.

For starters, the oil must perform several functions, not just help prevent engine sludge.

For that reason, oils contain a limited concentration of detergents (compared to an engine flush product) to ensure room in the formulation for other additives that protect against wear, fight oxidation, combat rust and more.

An engine flush product, on the other hand, is designed solely to clean.

AMSOIL Engine and Transmission Flush, for example, contains nothing but potent detergents, making it a more effective cleaner than motor oil.

Plus, it cleans at the molecular level, ensuring deposits are dissolved and properly exit the engine with the oil when it’s drained. This is important since some motorists fear that an engine flush will free large chunks and cause an avalanche of debris to clog passages inside the engine. AMSOIL Engine and Transmission Flush guards against this scenario.

Is an engine flush necessary?

A good engine flush can help loosen deposits and dissolve sludge, returning your engine to like-new condition.

However, in old engines with high miles, sludge may be the only barrier keeping oil from seeping through worn or cracked seals.

Removing the sludge exposes the seals for what they really are – junk. Soon, your engine begins leaking oil, and your mind instantly associates the engine flush product with an oil leak.

In reality, the seals were already bad; the flush simply revealed their true condition.

If you suspect your vehicle falls into this camp, leave well enough alone and skip the engine flush.

It’s probably not worth trying to revive an engine in such poor condition without first fixing the bad seals or other defects.

In effect, you’re choosing your problem: either sludge and deposits robbing performance or, if you clean the engine, the seals showing their true condition.

An engine flush is part of a good maintenance regimen

But that’s not to say an engine flush is never a good idea.

In fact, it’s often the first step in helping restore a neglected vehicle to top-notch performance. And, often when you buy a used vehicle, that’s what you’re getting – a vehicle whose owner found antiquing on Saturday afternoon more enjoyable than changing oil or dropping the transmission pan. Consequently, your “pre-owned” ride, while not complete junk, may boast a sketchy maintenance record.

In these cases, a potent, detergent-based flush can help prepare the engine for new oil, loosening sticky valves or rings and helping remove harmful sludge.

While not a required step when switching to AMSOIL synthetic motor oil, we do recommend flushing your engine if you want to give your vehicle a fresh start.

5 benefits of an engine flush

1. Prepares your engine for new oil

An engine flush helps loosen sticky valves or rings and remove harmful sludge and other contaminants.

By cleaning the engine prior to installing fresh oil, you ensure the new oil functions as intended and delivers maximum protection. The oil won’t last as long or protect as well if it must contend with sludge and deposits from the previous oil.

By the way, we don’t require use of AMSOIL Engine and Transmission Flush before switching to AMSOIL synthetic motor oil, but we recommend flushing your engine if you want to give it a fresh start.

2. Helps increase fuel efficiency

Contaminants circulating throughout the engine can lead to oil breakdown and increased viscosity – and higher-viscosity oil requires more energy to circulate throughout the engine.

Sludge and deposits on engine parts can also increase resistance, which wastes fuel to overcome. Cleaning the engine helps ensure parts move efficiently, maximizing fuel economy.

3. Helps reduce emissions

If deposits in the piston-ring lands cause the rings to stick, oil can migrate into the combustion chamber, where it burns.

This not only leads to harmful deposits, it also increases exhaust emissions as the burned oil exits the tailpipe.

A good engine flush helps free stuck rings and reduce oil consumption, in turn reducing emissions.

4. Helps reduce heat

Excessive heat is bad for your engine and the oil.

Extreme heat reduces engine efficiency while increasing the rate at which the oil oxidizes (chemically breaks down). Sludge and deposits act as insulators that prevent the engine from dissipating heat as designed.

Flushing your engine helps ensure it manages heat properly for optimum efficiency and oil life.

5. Convenience

This might not apply to every engine flush, but it applies to AMSOIL Engine and Transmission Flush. It delivers results after just one application. And it only takes 10-15 minutes to use.

Plus, you can safely use it in gas or diesel engines and automatic transmissions.

While some solvent-based flush products require a cumbersome disposal process, AMSOIL Engine and Transmission Flush uses a detergent-based formulation. As such, you can dispose of it easily with waste oil.

Engine Flush Products: I use AMSOIL Engine and Transmission Flush

Engine flush

For the record, I’ve used AMSOIL Engine and Transmission Flush on three different pre-owned vehicles in my time, and it’s worked great.

One of them, a 1999 Honda CR-V, accumulated more than 220,000 miles before rust forced me to replace it.

Another, an Oldsmobile Intrigue, ran great until a computer problem forced me to trade it off…for the CR-V.

The third ran great, but I sold it off after it, too, rusted out.

In sum, flush your engine if you want to give your vehicle a new lease on life.

AMSOIL Engine and Transmission Flush, as the name indicates, also works great for cleaning automatic transmissions.

Check out this post to determine if a transmission flush or pan drop is better for you.

But if you have any reservations about disturbing sludge or deposits that may be holding your old, high-mileage engine together, consider skipping it. It’s up to you.

How to perform an engine flush

If you are looking for the best way to flush your engine this weekend, here’s a quick video that will walk you through the process.

Originally published Jan 30, 2017.


  1. I like how you pointed out that an engine flush can help loosen and dissolve deposits and sludge. I imagine that having a sludge removal system that is contained in a trailer would be one way to make the sludge removal process more efficient. If I ever need this service, I’ll be sure to look for a professional provider of these kinds of systems!

  2. John, you made the following statement to a customer that suggested using ATF, 1/2 quart in the oil and running for 100 miles and draining. “ATF can disrupt the engine oil formulation and reduce its effectiveness. A good motor oil is a fine balance of base oils and additives that are designed to work together to fight wear, reduce friction, prevent deposits and provide cleaning power. Adding a foreign substance to the oil – tranny fluid, diesel fuel, an aftermarket oil additive – will throw off oil chemistry and possibly negatively affect wear protection, oil life or more. You may see a benefit in one area, but at what expense? 3) ATF can alter the viscosity of the oil, reducing wear protection. This likely isn’t an issue in your case since you’re running a higher-viscosity oil than what the engine manufacture recommends.”

    The above 1/2 quart represents only 10% of the total sump capacity, and only 1/75 of the time the ATF would be operated in the engine. Somehow you feel it will throw off the chemistry and negative wear protection, oil life or more. Seems that using a foreign substance such as AMSOIL Flush, with solvents and other ingredients can most certainly result in the affects you describe. In the case of the flush, upwards of 10-20% will remain in the engine for the entire oil change cycle, which can be 7500 miles, not a mere 100 miles.

    Sorry, but it appears you are not applying the same standard as you described to the other customer. I personally would never use ATF. Flushing the engine with 100% formulated, API approved, that meets manufacturer requirements will perform much better than leaving 10-20% of the oil from the previous OCI along with the same percentage of the foreign substance, as known as flush. One of my closest friends and mentor was petroleum engineer and AMSOIL direct jobber. He also advised against using any type of flush products, only fresh oil as the flush fluid.

    1. Hi Brian,

      AMSOIL Engine & Transmission Flush is a base oil that includes increased detergents. It does not include solvents. Unlike transmission fluid, it contains chemistry similar to motor oil, making it compatible.

      Adding a 16-oz. bottle of Flush to a five-quart (160-oz.) oil sump represents 10% of the sump volume. Our directions say to idle your engine for 10-15 minutes when using Flush and NOT to put it under load. The scenario above has the vehicle driving under load for 100 miles with ATF in the sump. That’s a big difference that could potentially affect wear protection.

      Even if 20 percent of the Flush product remains after draining the engine, that’s less than four ounces – insufficient to alter the oil chemistry enough to affect protection.

      All that said, simply don’t use Flush if you’re reluctant. While it helps give your engine a fresh start between oil changes, you’ll be fine if you just use a good synthetic oil.



  3. I have asked this before and AMSOIL responded by saying residual used oil and even the remaining amounts of the flush will have no harmful effects on the engine if run for another full oil change interval. Assuming that a high of 20% of oil and flush remain in the engine after a drain and refill, do you have any research or can point to any peer-reviewed information, scientific automotive journals that this old oil and flammable flush in the oil has no negative or harmful results? I would like to try the AMSOIL flush, and I have been a customer for a long time, but without knowing the type of solvents and quality of the carrier oil in the flush I am unwilling to take the risk or recommend it to anyone else. I recommend that everyone perform a Full Volume Oil Change as described in Machinery Lubrication publications. They maintain that the residual oxidized, contaminated, wear-metal-and-airborne-containing, and existing sludge, varnish and carbon, especially in GDI engines, does have an impact on the the new oil and engine. AMSOIL set yourself apart and share all the research to show this flush product is safe. I have learned my lesson many years ago to take most of the marketing and claims a company makes, with a grain of salt.

    1. Hi Brian,

      Thanks for reading the post and offering your insight. AMSOIL Engine & Transmission Flush is a base oil with increased detergent content (it doesn’t include solvents). It’s compatible with conventional and synthetic oil. Assuming an average sump capacity of five quarts (160 fluid ounces), a 16-oz. bottle represents only 10 percent of sump volume. Following our directions, the flush will circulate through the engine for 10-15 minutes before being drained. Even if assuming 20 percent is left behind, that’s less than four ounces of Flush in a five-quart sump. It’s not enough to negatively affect the oil.

      All that said, I appreciate your concern for protecting your vehicles. If you’re uncomfortable, simply skip the flush. While a beneficial part of engine maintenance, it’s not required so long as you’re using a good synthetic oil.



  4. I have a 2013 Kia Sportage. It’s not giving me any problems,but I went and got oil changed. They gave me a sheet recommending transmission flush, radiator flush and engine flush. What to do?

    1. It depends on your mileage on the car. Transmission fluids and coolants don’t need to be changed or flushed as often as engine oil. It sounds like a quick cash grab. If you want to save money, you can actually do it yourself.

  5. I have an engine with 250k miles, and oil changed every 3k miles with no performance problems. If i replaced 100% of the old oil using multiple oil drain and refills after allowing to circulate with a new full flow filter, similar to engine testing labs use for evaluating performance of lubricants, then used AMSOIL flush per instructions, would I see through inspection and be able to measure through oil analysis for particulate levels, color changes, contaminant levels, that would demonstrate the performance of the Engine Flush. I have seen dozens of Dealers make videos claiming how well it works, and showing customers how dark the oil it when in fact it is just the old and new oil mixing. I would love to see a video of the scenario described above, with crankcase inspection and oil analysis.

  6. I have a 1976 Corvette Stingray with an L48 engine and 350 cubic engine, with 76,000 original miles. When I start the car, I get the exhaust smell and a little exhaust fumes smell. Not being mechanically inclined I’m wondering whether or not an engine flush might help me with this problem. And suggestions would be greatly appreciated.

    1. Hi Tom,

      I can’t diagnose the problem over the Internet, but I can offer some basic ideas based on experience. It sounds like the engine is burning oil, which could be due to sticking piston rings. In that case, a flush can help loosen the rings and reduce oil consumption. However, it could also be due to engine wear, and a flush isn’t going to fix that. Operating under the principle of trying the easiest, cheapest fix first, a flush may help solve the problem, and it doesn’t cost much. If it were me, I’d try a flush and go from there.



  7. Hello, i reside in U.A.E. and we have very extreme climate. I have a 2015 Ford Focus ST (Turbo) that has clocked 135K Kms. I regularly change my oil 10W30 synthetic blend (semi) every 10K kms. Also i use the very best high octane fuel super from the very begining. Is the AMSOIL Engine Flush safe for Turbo and GDI (ecoboost) engines. Also at 135K km will my car benefit from the flush?

    1. Hi Narendra,

      Yes, AMSOIL Engine and Transmission Flush is perfectly safe for turbocharged GDI engines. How well your engine will benefit from a flush depends on its condition. The more deposits, the more the engine will benefit. It sounds like you’re taking good care of your engine, so it should be in pretty good condition. Given your climate, however, it’s likely some deposits have formed in the extreme heat. At your mileage, it’s a good idea to flush the engine prior to your next oil change to give it a fresh start.



  8. I have a 2004 Honda Element with 155,000 miles on it. I have always changed the oil with a synthetic 5-20 at 4000 miles. I am the second owner. It had 86,000 miles on it when I bought it. The check engine light has been coming off and on. I took it to the mechanic and he plugged it into the code reading machine. Spool Valve problem or some call it the V-tech solenoid. He replaced it and light is still coming off and on. Seems to be running fine though even when I accelerate hard. Some have mentioned an engine flush to clean screens. Does that make sense to you?

    1. Hi Larry,

      An engine flush will help clean deposits from anything the oil touches, so it’s worth a try in your case. Also, be sure to use a high-quality synthetic oil that will help prevent deposits in the first place. Prevention beats the alternative. After flushing the engine, I suggest upgrading to AMSOIL Signature Series Synthetic Motor Oil. That will help keep your engine clean and running properly.



    2. Hi Larry/John,

      Im replying to this post as I have the same problem. As matter of fact many Element owners are battling this issue with the VTEC. codes P2646 &P2647. I replaced that part several years ago. but prior to every oil change car engine light comes on and then we change the oil and its good. But this month the light came on a little earlier . We still changed the oil but the engine light still stays on and car is running poorly. rough idle etc. I called Honda service and they told us do not run full synthetic. We have been running synthetic blend however. Note this car was made to run on what i want call today regular oil that I grew up with. In reading the information on the flush it suggested with high mileage not doing the flush as it may cause greater problems? Is there anything else related to this code that could actually be the cause? Trying to determine next step and should it be the flush. Odd that a great majority of element owners have this same issue. We have 2003 element with 225K miles.

    3. Hi Ginger,

      I’m sorry to hear about the problems you’re having with your Honda. I can’t say with certainty what’s causing the light to illuminate, but I wonder if deposits have built up on the screens on the VVT solenoids? The openings on the screens are tiny, and even minute deposits can interfere with oil flowing through them, which can trigger a check-engine light. Another possibility might be that the oil’s viscosity is increasing during its service interval due to oxidation. Oil that’s too thick for your engine may fail to flow through the VVT screens. That would explain why the problem goes away after an oil change. Again, I’m thinking out loud here, and I can’t say for sure.

      Consider performing used-oil analysis right before changing oil next time. That will tell you if the viscosity has increased too much. It’ll also tell you if the oil contains other contaminants that could be leading to deposits.

      I can’t figure out why the tech told you not to use full synthetic oil; that has nothing to do with VVT operation. He/she may mistakenly believe synthetics are “too slippery” for use in VVT-equipped engines.

      As for the flush, it will help clean deposits on the VVT solenoids and screen (in addition to other areas of the engine). That, in turn, will help keep those components clean and working properly. However, you said you have reservations about flushing a high-mileage engine. Have you maintained it well with regular oil changes over the years? If so, you should be fine. If you don’t know the vehicle’s history and suspect it hasn’t been maintained very well, then I suggest skipping the flush. Personally, at 225,000 miles, I’d try the flush because you don’t have much to lose.

      Thanks, and best of luck.


  9. Hi,
    I am from Dubai. I have a doubt regarding Engine flushing. My car is 2018 model Mitsubishi (70k KMs at present) petrol engine. It is well maintained. Regular maintenance at every 10k KMs. Please advise whether engine flushing is advisable or required for my car.

    1. Hi Mukund,

      Are you using conventional or synthetic motor oil? Does your engine operate in severe conditions often (extreme heat, frequent short trips, stop-and-go traffic, etc.)? These factors play a role in the amount of deposits and sludge, if any, inside your engine. With 70,000 km on the engine, it’s likely a good idea to flush the engine just to give it a fresh start before your next oil change. It certainly won’t hurt.



  10. It is interesting that this post relayed to us that it is important for us to seek professional advice when considering an engine repair or overhaul. My brother has an old car. Before he decides on replacing the engine or repair it, I will ask him to bring it to the mechanic.

  11. Hi John

    My mechanic changed the oil from my car which had mixed with water and created a milk-like solids,after draining the oil he didn’t use the engine flush. Now the new oil appears to be the same as the one that had mixed, can the engine flush help my situation?


    1. Hi Sibusiso,

      Assuming the mechanic fixed the problem that had allowed water to mix with the oil, then yes it will help clean residual water/oil from your engine. It sounds like some contaminated oil was left behind after changing the oil; the flush will help clean it from the engine and restore performance.

      Thanks, and good luck.


    2. Probably not in this case mate. Milky oil indicates that a head gasket needs replacing. Sorry to be the bearer of bad news

  12. Hi i have an old 2006 hyundai lavita
    It has gone for 188 km until now and i didnt use any flush before
    Is it safe to use it now as you said in the post above for old cars sludge may be useful.
    I dont have problems in the engine at the moment so is it safe or not to use.

    1. Hi Hassan,

      If you don’t detect any mechanical flaws with your engine and have no reason to think excessive sludge is present, then Engine & Transmission Flush should work just fine in your engine provided you follow the directions on the label.



  13. Hi John, .
    I dropped and cleaned my lower oil pan. Also removed , cleaned and replaced my valve covers. So most of my oil is removed from the engine. 2017 Pathfinder
    The rear valve cover was very sludged up. How many quarts of cleaner are safe to add for a flush . Can you use 5q?

    Thanks Mike

    1. Hi Mike,

      Just follow the directions on the bottle, which is to use one full bottle in your case.

      Good luck,


  14. Hello, Is it best to use the engine flush in a cold engine or a hot engine. Is one better than the other or does it matter at all.

    1. Hi Bruce,

      The directions require idling the vehicle for 10-15 minutes after adding the flush product to your engine, so the engine will warm up during the process. It doesn’t matter if the engine is already warm or not prior to adding the flush.



  15. I am glad to know that engine flush can help us reduce harmful exhaust emissions from our engines. My husband just bought a boat and he was talking to me about the maintenance of the engine the other day. I will definitely let him know about using an engine flush for his boat engine.

  16. Hi ,I have been using 10w30 conventional motor oil in my Toyota Yaris for years. My question is I am thinking of switching to your XL oil or OE synthetic engine oil & my crankshaft oil seal has a leak, it leaks a quart in 21 days. Would it be a bigger leak if I switched to your synthetic oil or should I just let it be and leave well enough alone.

    1. Hi Sean,

      AMSOIL synthetic motor oil is fully compatible with seals and won’t cause them to leak. While I’m glad to hear you’re considering AMSOIL products, I recommend fixing that seal before changing to AMSOIL. Otherwise the car is just going to leak good oil onto the ground. Once it’s fixed, you’re perfectly safe switching to AMSOIL.



  17. Hi

    I recently bought a used Toyota Allion (2003) from Japan. Just a few days ago it started smoking whenever i use the reverse gear on a steep pavement. I also noticed the blue grey smoke whenever i accelerate more especially when trying to go over a pavement or driving uphill. Basicaly the vehicle is smoking when the vehicle needs more power and you accelerate. However when driving in a highway i cant notice any smoke. After consulting a mechanic, he noticed the blue grey smoke again on a cold start and also a lot of sludge on the oil cap. He advised using engine flush to get rid of the sludge as well as the blue/grey smoke. After reading the articles here, i am afraid the sludge might expose the worn out engine and the smoke even gets worse.

    Whats your advise?


    1. Hi Dean,

      It’s impossible to diagnose via the internet, but it seems like your engine is burning oil. That could be due to several reasons, like stuck rings or worn valve guides. Smoke from burning oil is more common when the engine is under load, like the conditions you mentioned. A flush can help loosen stuck rings, but it won’t cure bad valve guides.

      Do you have any reason to suspect the seals are worn? Do you notice oil leaks on the pavement after you’ve been parked a while? How many miles are on the engine?

      If you have reason to think the seals are worn, like an oil leak, then it makes sense to skip the flush. But, if it were me, I’d try the flush if I had no indication of bad seals.

      Best of luck,


  18. Hello AMSOIL
    Purchased a 2002 GMC Envoy with the 4.2 has around 185,000 miles. When engine warms up it tends to at idle have low oil pressure. I’ve found out after I purchased this this is a problem that is common with the 4.2 in trailblazer/envoy engines as the oil pickup tube screen gets plugged up with sludge or breakdown of sealant. Will the flush you make help clean this out as it is not easy to get the pan off as axle goes through it since its awd.
    Thanks Stephen

    1. Hi Stephen,

      AMSOIL Engine & Transmission Flush contains potent detergents that dissolve sludge. Yes, it’ll help clean sludge from your engine. Bear in mind, it’s not a “mechanic in a can,” however; while it will certainly help, it isn’t capable of fixing a mechanical defect, as no additive is.

      Thanks, and good luck.


  19. I own a 2005 Saab 9.3 Arc 2.0T convert. 150k miles. Was running perfect until I poured 1/2 a bottle of Lucas Synthetic oil additive for high mileage vehicles. Almost immediately dark grey(whitish,blue,dark) smoke started exiting the rear exhaust. The motor started sputtering and eventually stalled. Manual transmission, finally vehicle started but would not stay on. It would stall and was running very rough. Finally after a few minutes (maybe 15) I was able to limp it home. After 3 oil changes its gotten better but still not like before the additive(lucas). When I start the vehicle in the morning I get lots of greyish blue fuel smelling smoke until It heats up and then starts running ok for a while, but again it will start smoking or wont start after driving for a while. If I let it sit for about 30 minutes it will start up again and run okish. Will an oil flush help resolve the problem. I know I need to bite the bullet and bring to a real mechanic. THANKS

    1. Hi Gus,

      Unfortunately, we can’t diagnose your vehicle over the Internet; their are simply too many variables involved. As you say, visit a mechanic and find out what’s going on.

      As for the flush, yes it’s perfectly safe to use in your engine. Because I don’t know why your engine started acting up, I can’t say for certain whether the flush will help. But it’s an inexpensive first step toward resolving a potentially larger issue that will benefit your engine, too.



  20. Hi AMS Oil.
    I have a 2008 Cadillac CTS-V, direct inject. I purchased the Caddy in 2011 from a new car dealer coming out of a one owner, 3 year lease with 34,000 miles on it. Not sure what oil was used in it before I purchased it. The Caddy now has 92,000 miles on it. Around 38 – 40, 000 miles, I had an independent auto repair shop do a complete BG flush using BG flash products and a flush machine and had the Cady refilled with AMS oil, signature 5W30. There has only been two times that I used a different brand of full synthetic oil in the Caddy, they were Kendal-GT1 full synthetic , and Mobil 2. Since then the behave always used AMS oil. My tech who works on my car told me, since I always se AMS oil, that I don’t need to do an engine flush. I religiously change oil at 5,000 to 6,000 miles and a minimum at least once a year with Signature AMS Oil. Now since it’s been a few years and between 53 & 54,000 miles since the BG flush, do you recommend that I use a can of AMS engine/transmission flush before my next oil change? Thank you. John L’Ski

    1. Hi John,

      It sounds like you maintain your engine well and you use a premium synthetic oil. It’s unlikely your engine has accumulated significant sludge or deposits, unless there’s some mechanical defect at work I’m unaware of. It certainly won’t do any harm to use AMSOIL Engine & Transmission Flush at your next oil change, and it’s inexpensive insurance to help maintain that like-new feeling with your engine. It’s ultimately up to you, but I recommend a flush.



  21. Based on oil analysis and confirmed by labs, anywhere from 10-20% of used oil will remain in a modern engine. The days of single cam, solid lifters, rocker arm valve control is over. We now have dual over head cams and VVT is driven by multiple oil galleries for each bank of the engine, larger main oil galleries, cartridge filters that sit high in the engine, oil coolers, turbos, and other areas where oil be retained and not drained in brief oil change. In addition to the flush, would you recommend performing a second flush with straight API certified oil of the correct viscosity to remove 99% of the old oil and now this product? I have oil analysis from Polaris labs showing retention of 20% wear metals, air borne contaminates, fuel dilution, and depletion of additives, loss in viscosity, total base number and increase in oxidation within 30 minutes of engine operation due to fluid mixing (new with old). Also particle counts were significantly higher in the 2-6 micron range after a standard oil change.

    1. Hi Brian,

      You make some good points about the challenges of removing all the oil from some modern engines. Our research and development on our flush product showed excellent results after a single oil change. Again, residual flush left behind in the engine won’t cause harm. However, if you want to remove as much of the old oil as possible, by all means perform a second flush. In most engines, however, a second flush isn’t required.



  22. 2005 honda accord v6 3.0liter automatic, 280,000miles, one owner (me):
    All rec maintenances up to date except timing belt (still on 2nd timing belt and water pump)
    Recent engine oil leak, mechanic determined oil pan gasket, replaced entire oil pan, still have leak. Mechanic not sure of origin. Using oil leak stop with reg oil/oil filter change. Not severe oil leak but have received 2 quotes on determining and (?) Repairing oil leak. If repair to be done, any benefit to engine flush? Is flush done with oil leak repair again?

    1. Hi Bretta,

      Sure, an engine flush can help clean the engine of any accumulated sludge or deposits. It sounds like you’ve maintained your car well, so you should be fine.



  23. Hi.
    After a lot of researching, I decided to switch over to AMSOIL Signature 0W-20, on my 2014 Honda Civic 4dr.. I’m the first and only driver since I bought it brand new in 2014. I have only allowed Honda to change my oil. every 5,000 miles, since the. I’m concerned that if I change the oil myself, or if I use the flush detergent, it’ll also void the warranty. is this true?

    1. Hi Edward,

      Thanks for trusting your Civic with AMSOIL. No, changing oil yourself or using a flush product will not void your warranty. To void the warranty, the manufacturer has to prove that whatever product you used actually caused a problem. Find out more about warranties here.



    2. Edward,
      I had a Honda CRX. I flushed it twice and had no issues. The first time was around 130,000 miles and the second time was somewhat over 220,000. I sold the car, still running, at 336,000 miles. Still on the same cutch as well as nothing done to the engine at all. I hope you like that car if you plan on driving it until it wears out. I also use synthetic oil in all my vehicles and after 50,000 miles I always use an additive like teflon.

  24. I have a 2003 dodge dakota 4.7L, and has 218,000km on it.
    I recently changed the crankshaft seal because it was leaking.

    Would doing a flush possibly crate more oil leaks?

    1. Hi,

      As explained in the post, performing a flush may remove sludge from old, worn seals and cause them to leak. I don’t know how well your Dakota has been maintained over the years, so it’s impossible to make predictions. Was the crankshaft seal leaking because it was damaged or because it had dried and become brittle due to inactivity? If the latter, it’s possible other seals could fail, too.

      If you have reservations about flushing the engine and revealing the poor condition of the seals, don’t bother.



    1. Hi Roman,

      Three-four bottles for a 10-gallon sump should suffice. Be sure to watch the overall oil level on the dipstick so you don’t over fill the sump.



  25. Hi Amsoil, I recently purchased a 2008 BMW 320i which has about 120K km , I had to replace a valve cover gasket and it revealed soft powdery and flaky black sludge on the non moving surfaces, mainly buildups in boltheads, springs and and corners. Performance wise it is ok . I do not know the service history ( infrequent prob) but i will use full synthetic oil . for my first service. I wish to do a flush coupled with frequenct servicing and filter changes to remove the sludge. Will amsoil remove significant sludge depoists.

    1. Hi Dave,

      Yes, AMSOIL Engine and Transmission Flush will help clean sludge from your engine. It’ll help prepare the engine for fresh oil so you can get the best protection from your oil change.



  26. retired tech
    january 6 2020
    hi, i purchased a 2006 dodge ram with a 4.7 engine in it, i have been hearing a little knocking noise when first started. after a while it quiets down, i suspect oil sludge.i do not know how well the engine has been serviced i have only owned it for two weeks. would a flush help with my problem?

    thank you

    1. Hi Richard,

      Yes, AMSOIL Engine and Transmission Flush can help remove sludge and quiet engine knocking or ticking as a result of sludge. Your truck sounds like a perfect candidate for this product.

      Good luck,


    2. ticking on cold start that goes away when warm is often times related to a exhaust manifold leak not an internal engine noise. if you consider its a dodge the exhaust manifold leak or broken bolt is more likely than piston or rod issues.

  27. In modern engines at least 10-20% of the oil will remain in the engine after a simple drain and refill. Will the flush that remains in the engine after the 5-7K miles alter and disrupt the additive package and the binding agents used in the original oil formulation. Would you recommend a second drain and refill to get a full 99% replacement. Machinery Lubrication publication says that a Full Volume Oil Change, is more beneficial as all the additives and detergents are able to be used for its purpose (removal of varnish and sludge) rather than trying to counteract the 10-20% of used oil over the next full service life.

    1. Hi Brian,

      Residual oil mixed with the flush product won’t cause adverse effects to the engine. Just follow the directions on the label and you’ll be fine. There’s no need to drain the engine a second time.



  28. I have a 2009 Acadia with P0008. Timing chains and gears recently replaced. I read some blogs that recommend oil system flush. Do you think this product is sufficient to resolve my issue?

    1. Hi Mark,

      I don’t know why GMC had timing issues with certain GMC models, including yours. A flush product isn’t a miracle worker and isn’t capable of solving a complicated mechanical issue like this. If GMC recommends flushing the engine to help clear out any sludge that may be preventing proper lubrication, then certainly our product can help. Just remember it’s not a “mechanic in a can,” however, so temper your expectations accordingly.

      Good luck,


  29. Hi,
    My toyota sequoia has about 208,000 miles on it with recent oil changes using amsoil signature series and wix filter. Mechanic recommended engine oil flush at about $750. (It’s never been done on this vehicle and its had regular oil/filter changes, I’m original owner). Could I just add engine flush product and drive the 10-12 miles to the mechanic to do regular oil change?

    1. Hi Prent,

      We don’t recommend placing the engine under load while the flush is in the crankcase. Simply idle for 10-15 minutes and drain the oil.



    1. Hi Shaun,

      I’m unsure what a “freelander tds auto 54plate” is. Can you provide make and model please?



  30. Hi,
    I have a 2013 Impala 3.6 GDI with 110k and it has the typical oil consumption, loss of performance, gas mileage and carbon coked. valves. I regularly change the oil and always run full synthetic. Will this flush help restore performance?

    1. Hi James,

      Yes, flushing your engine should help restore performance. The flush won’t, however, clean the valves since oil doesn’t reach them. It will help free stuck rings, which can help reduce oil consumption.



  31. Hi,

    Thanks for the article. I have wondering if it is necessary to flush one of my vehicles. It is a 2016 BMW X3 with 49,768 miles. One of my questions is how would one ensure all the flush product is out?

    I currently use the oil from BMW.


    1. Hi Ayo,

      Whether a flush is necessary depends on the vehicle’s maintenance history, what kind of oil you’ve been using, driving conditions and other variables. With nearly 50,000 miles on the engine, it’s a good time to give it a cleaning. The flush product drains out with the oil. While a minimal amount may get left behind in the engine, it’s not enough to cause concern.



    1. Hi Niaz,

      Yes, it’s perfectly safe to use in your engine. Just follow the instructions on the back label.



  32. I have a 2014 Kia Sportage I bought used nearly 3 yrs ago. It had 15k Mike’s then & has 38k now. I am a hard working single mom, so have neglected getting my oil changes. My check engine light came on & took to dealer. They say I need a new motor & extended warranty likely won’t cover since I have not maintained it. They do not recommend a sludge remover as it may cause other problems. I have verbally confirmed this with another trusted mechanic. However, I am desperate as I cannot afford the cost to repair or trade in. What are your thoughts on trying this? You’ve given me hope since the vehicle is not too old or too high in miles. However you say to do it prior to changing the oil. The dealer just changed the oil today. Check engine light went off temporarily but came back on. Is it safe to do this & then take it for another oil change? Help!

    1. Hi Angela,

      I’m sorry to hear about your problems with your Kia. While a good flush product helps remove sludge and cleans an engine, it’s important to remember that it’s not a “mechanic in a can.” Flushing the engine likely won’t reverse months or years of neglect. However, if I were in your situation and the dealer told me the engine required replacement, I’d try the flush as a last-ditch effort to prolong the engine’s life. At that point, you have nothing to lose. Again, though, I’d ensure the warranty will not cover the engine replacement first. If the dealer says there is absolutely no hope of warranty coverage, then you might as well try the flush. Feel free to call AMSOIL Technical Services at 399-715-TECH and they can help you, too.

      Thanks, and good luck.


    2. Unless your Kia has been used for heavy duty towing or something that really stressed the engine, then I highly doubt that your engine is shot. I would go to an auto parts store that will check out what is causing the check engine light by using an analyzer on it. Most places will do this for free. The only reason your light would come on for an oil problem would be just a reminder to change the oil. Don’t consider replacing your engine without a 2nd or 3rd opinion from different dealers. And don’t mention what the first dealer told you. Too many repair places will take advantage of someone who isn’t savvy on car problems. Many repairmen are good but I’ve found places that tried to take advantage . And I’ve been working on my cars for 42 years now.
      Good luck ! I hope you get this problem fixed without paying a lot.

    1. Hi,

      We recommend simply idling the engine. There’s no need to engage in “high” idle for the product to work.



  33. It’s good to know you can dissolve engine sludge with the right mixture of detergents. My engine is really looking worse for wear because I haven’t had it cleaned since I got my car. I want to fix it soon so that I can get back to driving a car that isn’t dying.

  34. Hi,
    Can this be used with a car that has an oil cooler?
    The engine holds approx 4.5 litres BUT a further 4.5 litres via the remote oil cooler (inc pipes etc)
    If I use the engine flush approx half would remain within the oil cooler system.
    Is it advisable to use the engine flush?


    Lotus owner

    1. Hi,

      In this case, we recommend changing the oil three times to ensure removal of all the flush product. Leaving that much flush in the system isn’t advised since it could reduce wear protection.



  35. I just purchased a 1998 Ford Ranger 3.0 6 cylinder with 110,000 miles on it. I want to swap over to synthetic. would you recommend the engine flush or by pass it also what weight would you suggest to use on this vehicle ? looking forward to your input. thanks

    1. Hi Brian,

      We recommend 5W-20 in your Ranger.

      Yes, your vehicle is an ideal candidate for Engine and Transmission Flush, especially if you don’t know its maintenance history. The miles are relatively low, so the engine should be in solid shape. We recommend flushing prior to your next oil change to give the engine a clean start.



  36. Hi John,
    I am new to AMSOIL and I plan to switch all my vehicles to the Signature Series. I would like to do the engine flush before switching. I normally warm my engine oil before changing. My question is, is it okay to use your engine flush in a warm engine?

    1. Hi Bruce,

      Welcome to the team.

      Yes, it’s perfectly safe. In fact, the directions on the bottle tell you to pour its contents into the engine and idle for 15 minutes.

      Best of luck,


  37. It’s awesome that you mentioned that it can increase fuel efficiency. My neighbor needs a new engine and he asked me for help researching. In my opinion, he should make sure he cleans it as you mentioned.

  38. Hi John, I’m new to Amsoil myself. In fact I just ordered a case of your 10w30 small engine commercial oil. My plan is to convert all my small engines over. Some I use for work, others personal. My question is on some of my work engines(mud pump, welder/generator) run hours upon hours daily. I’ve changed the oils(DINO) pretty much monthly due to high use of engines. By switching to your synthetic, I’m pondering using a flush. I know its not necessary, but I want to get maximum results. I’m a little worried the flush will reveal problems with these high hour engines? Is that worry valid? In your opinion should I let the Amsoil remove the deposits over repeated oil changes and time? Thanks for your thoughts.

    1. Hi Dan,

      We don’t recommend using Engine and Transmission Flush with small engines. Some small engines barely use a quart of oil, and adding a bottle of flush would dangerously dilute the oil. Attempting to meter out a prescribed amount of flush is also problematic unless you know the exact sump capacity and have measuring devices on hand. Plus, as said in the post, if you’re concerned about a flush product revealing bad seals on a high-hour engine, skip the flush.

      Instead, just let the oil’s detergents naturally clean the engine, as you suggest. Synthetic Small-Engine Oil is a great choice for what sounds like a fleet of heavy-use applications. We recommend the oil for up to 200 hours or one year, whichever comes first.

      Thanks for giving AMSOIL a try, and best of luck.


    2. Thanks John. I pretty much guessed an entire bottle of flush wouldn’t be wise. LOL. Thanks again. Looking forward to trying the product..

  39. Unless you can inspect the gap between rod bearings and rods to ensure there is absolutely no carbon buildup, never use flush on an engine with high mileage – even if you were good about changing the oil.

    The flush chemicals dissolve carbon buildup and if it dissolves the carbon buildup between the rod bearings and rods, it effectively increases the gap there. This means the likelihood of your car throwing a rod sometime in the future is greatly increased.

  40. Hi,

    My Suzuki Swift 1.4 GLX ( Model Year 2016) was not service for almost a year and when the warning lights was ON, i send it to the workshop to be service but the mechanics says that my car need to be overhaul because too many thick sludge. Flushing wouldn’t do any good.

    Is this true or can i still flush it with AMSOIL and fill in with new oil ?

    1. Hi Darren,

      Are you still driving the car now? If so, I recommend getting a second opinion from another mechanic or the dealer before proceeding. If a knowledgeable mechanic has looked at the engine internals and recommends an overhaul, it’s unlikely any chemical flush product will help an engine in that poor of shape.



  41. Hi John,

    Thanks for your response! In regards to your comment below:

    “If you’re concerned about piston and valve deposits, try a bottle of AMSOIL P.i. It’s designed to clean fuel-system and combustion-chamber components.”

    Would this product you mentioned above work on a GDI engine? It looks like it’s a treatment that you put into the cars gas tank.
    Since the fuel injectors are inside the combustion chamber of each cylinder on a GDI engine, how would the product get to the intake valves? There are no port injectors on the 2.4L GDI Hyundai engine.

    Thanks again,


    1. AMSOIL P.i. is a highly concentrated deposit cleaner designed for use in both port and direct-injected engines. However, due to the design of GDI engines, fuel additives do not have an opportunity to reach the back side of the intake valves. It will, however, clean components within the combustion chamber, resulting in optimal combustion and fewer deposit-forming byproducts.



  42. Hi John,

    I had another question so thanks for the help in advance! Will this product clean the backside of the intake valves on a GDI engine? Obviously the regular “gas tank” fuel injector additive won’t work for GDI engines due to the placement of the fuel injector (port vs direct). As such, GDI engine are notorious for carbon buildup on the intake valves…



    1. Hi Jeremy,

      AMSOIL Engine & Transmission Flush won’t clean the backs of intake valves since it never comes in contact with them. To your other points, it does help loosen stuck rings and valves and can help reduce oil consumption in engines with stuck rings. However, with only 50,000 miles on your engine and given its maintenance history, I doubt you have stuck rings. Remember that some oil consumption is “normal.” A small amount of oil lubricates the cylinder walls and rings, meaning it’s exposed to extreme combustion heat and will burn. In fact, some automakers consider it “normal” for an engine to burn a quart of oil every 3,000 miles or so. Each automaker is different, however, so you may want to check with Hyundai to see how they define “normal” oil consumption.

      It certainly won’t hurt to use Engine & Transmission Flush before your next oil change to ensure the engine is as clean as possible. If you’re concerned about piston and valve deposits, try a bottle of AMSOIL P.i. It’s designed to clean fuel-system and combustion-chamber components.

      Thanks for reading,


  43. Hi John,

    I have owned my 2016 Hyundai Sonata Sport 2.4L GDI since basically new. It ran “normal dino oil” for probably 150-250 miles when brand new. Since then I have always used Amsoil SS 5W-20 or 5W-30 and Ea15k oil filter in the engine. Lately I’ve been changing the oil and filter closer to 10k miles instead of 15k miles as the engine is burning around 1-1.5 qts ever 10k miles (I’ve been monitoring and topping off as needed). The car is now approaching 50k miles on the odometer. I’ve been thinking about using this Amsoil engine flush before my next oil change just to make sure there is no sludge or gunk or clogs. I know Amsoil SS oil provides ultimate protection, but I was wondering if you think doing this engine flush may help my oil consumption or at the very least ensure the valves and pistons are as clean as they’ll ever be going forward? I appreciate any input.



  44. Hi John Baker
    I have inquiry what regarding is it safe to use engine flush amsoil for 19 year car lexus Ls400 model 2000 with 470k km.. Engine run OK but some deposits can see from engine fill cap.
    Do I need open oil can for engine and clean strainer?
    Is cause clog or not?
    Is it affecting valve stem seal?
    My car burning 1.6 liters for every 10k change oil which decent amount for old car
    Thank you for your great reliable products and competitive oil brand in market

    1. Hi Abdulaziz,

      Congratulations on getting that many kilometers on your car!

      It’s perfectly safe to use AMSOIL Engine and Transmission Flush in your engine. However, no one can predict with perfect accuracy how your engine will respond to the flush. There’s no way to know for certain if heavy deposits or sludge are present inside the engine without disassembly or scoping it with a camera. There’s also no way to predict if removing deposits or sludge will reveal bad seals.

      In the end, it’s your judgement call since you know the history of the engine better than anyone else. If you have any reservations, skip the flush.



  45. After running the Amsoil Engine & Transmission Flush for 15 minutes, and draining the 5w-30 Amsoil Signature Series oil; is there a problem with adding the: CERA TEC Engine Oil Additive (300ml Can) – Liqui Moly LM20002 to quiet engine noise and a 200,000 worn engine?

    Does Amsoil carry a product similar to the: —1— CERA TEC Engine Oil Additive (300ml Can) – Liqui Moly LM20002; OR —2— MoS2 Anti-Friction Engine Treatment (300ml Can) – Liqui Moly LM2009 ?

    1. Steve,

      It sounds like you’re asking if you can install an aftermarket additive after draining the oil and flush product. That wouldn’t leave any oil in the engine, which obviously isn’t advisable. Simply put, we don’t recommend aftermarket oil additives with our oils. Period. However, it’s your car and you can do whatever you want. Just be mindful that using an aftermarket oil additive with AMSOIL synthetic motor oils will void the AMSOIL Limited Warranty.

      If you have more questions, please call AMSOIL Technical Services at 715-399-TECH and they can take care of you.



  46. I have 2011 C320 diesel, but it sometime bring out white smoke,my mechanic advice I use engine flush, your professional advice will really be appreciated…

    1. Hi Victor,

      White smoke often occurs when there is either too much fuel injected into the combustion chamber or insufficient heat to burn the fuel. Un-burned fuel travels through the exhaust system and exits the tailpipe, which produces the scent of rich, un-burnt diesel. Other causes of white smoke include lack of compression or water/coolant entering the combustion chamber.

      Whatever the cause, you’re perfectly safe to use AMSOIL Engine and Transmission Flush in your diesel.



  47. Amsoil Engine and Transmission vs. P.i. Performance Improver Gasoline Additive.
    1- Which product is better for cleaning the sludge of a car’s PCV System without removal of the PCV hose and valve?
    2- How many bottle treatments would I start to see a semi-significant improvement in engine performance?

    1. Hi Steve,

      No additive is going to clean a plugged PCV. You need to replace the plugged PCV valve and manually clean the hose.

      After you replace the PCV and clean the hose, consider using AMSOIL P.i. in the gas tank and Engine and Transmission Flush for the next oil change to clean up deposits left in the engine.



  48. I have a 2000 Volvo S80 2.9 Non-Turbo with 113K miles. My volvo runs efficiently immediately after an oil change, but seemingly lose horsepower after approx. 5000 miles after an Amsoil 5w-30 Signature Series oil change. I suspect that the PCV system is clogged with sludge.
    1- Would the Amsoil Engine and Transmission Flush clean out the sludge, and how many flushes would you recommend?
    2- Do you recommend the WIX or the Mahler Oil filter recommended on your website?
    3- Would you recommend an oil change after 5000 miles?

    1. Hi Stephen,

      Engine and Transmission Flush is not going to clean a PCV system since it is not submerged in the engine oil. The flush will help clean any deposits inside the engine, which may be helpful.

      The PCV valve can be replaced, and the hoses can be cleaned with a parts cleaner or degreaser.

      The MANN HU819X is the only oil filter AMSOIL offers for your application; we no longer offer the WIX 57021.

      If using AMSOIL OE Synthetic Motor Oil, oil changes can be in the 5,000-mile range. AMSOIL XL Synthetic Motor Oil and Signature Series Synthetic Motor Oil can provide longer drain intervals.



  49. I have a 2008 sequoia which has engine sludge (can see deposits on dipstick). Nearing 150k miles. How likely am I to cause bigger issues by trying to clean out the sludge (ie removing sludge which may then lead to gasket failure). I don’t want to try to help prolong the life of my engine and end up causing it to fail earlier.

    1. Hi Andy,

      It’s impossible to predict each individual case. It depends on the condition of your engine. Is there any evidence of seal or gasket leakage? If you suspect sludge is “papering over” the seals or gaskets, then take caution and skip the flush. I can say, however, that I’ve used Engine and Transmission Flush in engines with more than 150,000 miles with no issues. Each vehicle is going to be different.



  50. Certain components like the engine, transmission and the cooling system need to be flushed after a certain time interval to remove the deposited contaminants which have negative impacts on the performance of those components. Besides, a car should be subjected to an inspection on a daily basis which helps us to identify and fix the mechanical abnormalities associated with the different components of the vehicle and any signs which indicates that the vehicle has some sort of mechanical issues should not be ignored. The reason behind the appearance of such a sign needs to be identified and repaired in time to keep the vehicle in working order.

  51. What happens to the excess engine flush in the system when the oil is drained and replaced with new oil and filter? Does it evaporate or is the excess so little that it is not something to worry about?

    1. Hi Vernon,

      AMSOIL Engine and Transmission Flush is a highly concentrated detergent-based additive that is designed to mix safely with motor oils. Therefore small amounts of flush left in the engine after draining the oil will not have a negative effect on the new oil added.



  52. Thanks for highlighting the benefits associated with the engine lubricant flush. The lubricant used in the engine plays a critical role in its performance and any sign which indicates that the engine has some sort of malfunction shouldn’t be ignored. Deposition of sludge has negative impacts on the performance of the vehicle. So, the condition of the engine oil should be inspected and if necessary should be replaced with suitable substitutes to keep the engine in working order. Besides, the engine should be subjected to an inspection after a certain time interval and the inspection should be carried out by well-trained professionals.

  53. Hi John.

    My Accord CD5 was affected by flood last 2 weeks ago. And the engine oil was ingress by water. Would your product can flush the mixed oil and water in the engine? Fyi, I had flush my engine with the engine oil also before.


    Best Regards,

    1. Hi Hamizan,

      I’m sorry to hear about your Accord. Your best bet is to change all the fluids, run the vehicle for a bit, then change them again. You may even have to repeat the process if needed. Although AMSOIL Engine and Transmission Fluid won’t help remove water directly, it will help remove any sludge that had already accumulated, in addition to sludge that may have formed due to water contamination.

      Best of luck,


  54. I have a 2000 F150 with a 4.2 v6 that when you start it it shows no oil pressure. Aftet 15-20 seconds it will come up then drop again. Turn off & restart it does same thing but when oil gauge comes up it will stay up above midrange on gauge. It has 223,000 miles and except for this problem it seems fine.

    1. Sounds like a gauge issue. Install a mechanical oil pressure gauge and see what is really happening.

  55. Just purchased a 2015 VW Passat with a 1.8 tsi gas engine. Had some issues with the engine light coming on. Recently had the intake cam replaced. While they had the engine apart, they said it had some engine sludge build up due to poor maintenance from the previous owner. Which they say had caused the problem. Would your product be safe on this particular engine to get rid of the sludge and help give the engine a new lease on life?

    1. Hi Eric,

      Yes, AMSOIL Engine and Transmission Flush is safe to use in your VW.

      Good luck,


  56. Hi,

    I currently own a 2011 Range Rover Supercharged 5.0 (85k miles) and recently had an issue with a local Import garage. I do not have the luxury to take it to the LR dealership as its 200
    miles away.

    My problem surfaced about six weeks ago when my engine started to shut down with a “Restricted Performance” warning. I had it towed to my local Import garage where they have serviced my
    RR many times. After a few days, they called me to tell me I needed a new timing chain. However, I informed them I had the timing chain replaced the previous year ($4500) so asked them to dig
    deeper. After another week they told me another gear (actuator??) was bad and needed to be replaced as well as a timing chain tensioner due to wear. Unfortunately, the actual labor
    involved in this work is very similar to the labor for replacing the Timing Chain… grrr

    Long story short – it took the shop another a week to make the repairss. However, when I went to pick up my RR, as well as pay the hefty bill, they walked me thru additional issues/concerns
    they found during their work. The primary issue, from their perspective, was all the “sludge” found inside the engine from the poor maintenance from the original owner. Because of the
    sludge they believe this is causing other components (valve solenoid) to stick triggering the sensors – check engine light.

    They have no idea where to start with cleaning the sludge and recommended tearing it apart and cleaning as they go. However, they would not guarantee this would fix the issue. Only a
    total engine replacement would work. At this point, I have no doubt they are trying to get as much money from me as possible before I take/tow my RR to the dealership. I am hoping that this
    Engine Flush might work like magic and save me $5,000-7,000 in repairs !!!

    Based on the above, I had a few questions:

    1- Is your product safe to use in my RR Supercharged engine?
    2- if so, do you believe using this product will help remove the “sludge” causing issues with the engine components
    3- how often can I use this “flush” and how much time should I allow between each flush?

    1. Hi BClevenger,

      1. Yes, AMSOIL Engine and Transmission Flush is safe to use in your Range Rover.
      2. Yes, the concentrated detergent package in AMSOIL Engine and Transmission Flush is designed to help remove sludge deposits that can lead to accelerated engine wear and poor performance.
      3. AMSOIL Engine and Transmission Flush is safe to use with every oil change. However, the frequency at which you change or flush your oil again is up to you. If you were told the amount of sludge is significant, then we recommend flushing the engine twice over the manufacturer’s recommended drain interval for good measure. Once you have flushed your engine, consider switching to AMSOIL Signature Series 5W-20 Synthetic Motor Oil to ensure the best protection and cleanliness for your Range Rover and continue to change your oil at your manufacturer’s recommended drain interval. I should point out that Engine and Transmission Flush isn’t a “mechanic in a bottle” and won’t fix any mechanical issues already present.

      It’s important to note that sludge does not form from motor oil on its own. It may simply be from lack of maintenance from the previous owner or it could be due to contamination from glycol, dirt or other contaminants. Performing oil analysis can help you determine what is causing the formation of sludge.

      Best of luck,


  57. I have a neglected(10-15k miles since last oil change) 2007 Scion TC. Turns out loaning your car to your nephew when you’re abroad for 2 years isn’t the best idea, but I digress. I’m considering AMSoil Engine Flush to hopefully mitigate some of the damage caused by the neglect.

    I suspect, probably accurately, that I fall in the “Leave well enough alone” category but I’m interested in your thoughts?

    1. Hi Edward,

      Not necessarily. The “leave-well-enough-alone” category includes vehicles that have sat undriven for long periods of time so that the seals tend to dry out. It also includes engines that have known sludge buildup due to years of poor maintenance. Your 2007 Scion sounds like a good candidate for Engine and Transmission Flush.



  58. I have a 2004 f250 with the 6.0. Is this product good to use on this engine with the stiction issues with the 6.0 issues will this product help clean the oil side of injectors.

    1. Hi Matthew,

      I reached out to our diesel technical product manager, and here’s what he said:

      In general, yes AMSOIL Engine and Transmission Flush will help remove deposits on the oil-side of the injector to keep the spool valve free to move. The real question is, does your injector suffer from deposits or wear? This HEUI injector can suffer from both. Our flush product will clean deposits but cannot fix worn injectors that bind. That is a design failure of the injector. Ultimately, engine oil and fuel additives may not fix the injector issues and an injector replacement may be necessary.

      Here’s what we recommend:

      Step 1: Use AMSOIL Engine and Transmission Flush to perform a complete cleaning of the engine and the oil-side of the injectors.

      Step 2: Use Signature Series Max-Duty Synthetic 5W-40 Diesel Oil to ensure your injectors remain clean and the oil provides the best wear protection possible. Plus, the 5W-40 is an excellent choice to help build proper fuel pressure at start-up and in the colder temperatures.

      Step 3: Perform regular oil changes using a high-efficiency oil filter such as an AMSOIL Ea Oil Filter.

      Finally, if you are trying to keep the injectors clean, don’t forget about the injector nozzle and keeping the fuel flowing as Ford intended. Using a concentrated dose of diesel fuel additive, like AMSOIL Diesel Injector Clean, will help keep the injectors flowing like new.


  59. I have Jetta Mk6 TDI AT with DSG done around 50000 kms. Will Amsoil engine & Transmission flush cause any damage to DSG transmission. These are complicated units.

    1. Hi VY,

      Unfortunately, we don’t recommend AMSOIL Engine & Transmission flush in DSG transmissions.



  60. Thanks for sharing such an important article about the importance of engine flush. The engine is considered as the heart of the vehicle which needs regular maintenance to work properly. The engine needs lubrication to work smoothly. However, deposition of debris influence the performance of the engine in a very adverse way. So, the engine should be flushed after a certain time interval to work effectively. The quality of the lubricant used in the engine should be inspected at a regular interval and if necessary should be replaced with suitable substitutes.

  61. Yo Amsoil, My 94 Dodge Cummins has 250K plus miles. I am going to install a Micron filter to keep the oil clean. I have run Hot shot Secret in this last oil change. Should I replace the oil filter before I use your cleaner or is my current filter sufficient enough to catch all the sludge and crap that will be cleaned out with your flush? I want to protect my new turbo as well as my engine.

    1. Hi Turbo Terry,

      Use your current oil filter with AMSOIL Engine and Transmission Flush. It should be sufficient to catch any sludge and debris removed during the flushing process. Just be sure to change the oil and filter following the use of Engine and Transmission Flush per the directions on the label.



  62. I have a 2004 Porsche Boxster S with 117 k miles. It has developed lifter ticking. I am very leary about using an engine flush. If I lose a bearing or ring I am looking at close to 20K for a new engine. What are your thoughts?

    1. Hi Emmanuel,

      There should be no risk of internal engine damage if the recommended instructions are followed. Many different things can cause lifter ticking, including oil deposits in the top end of the engine. AMSOIL Engine and Transmission Flush is designed to remove these harmful, performance-robbing deposits. However, it’s not a “liquid mechanic,” so if the lifter tick is due to a mechanical issue, Engine and Transmission Flush won’t fix it.

      I hope this helps.



  63. Hi,
    Just had a repair shop do an engine flush on my 2009 Toyota Camry without asking first. I’ve read a variety of stories online so I’m very nervous right now. Car overheated unexpectedly in the desert few weeks ago. Had it towed to this repair shop where they replaced the head gasket, machined the head, replaced the water pump, and then the radiator. I picked it up last weekend only to be told I needed to bring it back in a few days because they did an engine flush and still needed to put the thermometer in. Sounds like they left the engine flush in the engine for a few days. They also forgot to attach the air intake to the air filter compartment (found that in my trunk). My friend took it back today (2 days later, as instructed) so they could finish it up. The engine light came on this morning before taking it, which they contributed to not having a thermometer in it. Now he’s telling me I need an oil change within the next month. Shouldn’t they have done that after the engine flush? And is it a good thing to leave it in that long? I’m very nervous about driving this car and I live 2 hours from where its at now.

    1. Hi Kristine,

      I don’t know what brand of engine flush the mechanic used, but I can tell you that we recommend changing the oil immediately following use of AMSOIL Engine & Transmission Flush. We also caution against putting the vehicle under heavy loads while the flush is in the crankcase. The flush alters the motor oil chemistry, which can compromise wear protection. That’s not a big deal if you use the product according to the instructions, but it can be a problem if you drive the car for extended periods with the flush in the crankcase.

      Bottom line: If I were you, I wouldn’t drive the car until the oil has been changed. Also, this mechanic’s practices have me scratching my head. I’d go somewhere else closer to home. If their work (or lack thereof) damages the car, you may have to seek legal action.



  64. I have a 2011 Buick Regal 2.0liter turbo with 105k miles. The check engine light went on – MAF sensor. That was changed but did not correct the problem. We checked the oil, which turned out was filled with sludge. I had followed the GM oil monitoring software in the car, which recommended longer than typical milage between changes. I followed this program, changing the oil sooner than the software recommended, typically with about 25% oil life remaining, and typically10,000 – 12,000 miles. I realize this is high, but I was being environmetally sensitive and was following the GM oil maintenance program. GM will not do anything because the car is out of warranty, despite the fact that the problem is due to their oil monitoring algorithm. GM”s rep blamed actually the problem on me. (This is what I get for loyally buying an American brand car.) I replaced the oil twice since the problem arose to no avail. I tried an oil additive intended to help clean away sludge, which helped some but did not cure the problem. Would Amsol be recommended after this history? Do you think it might have a chance to cure the issue?

    1. Hi Len,

      Yes, you can use AMSOIL Engine & Transmission Flush in your engine. While it’s great for removing sludge, keep in mind that the product isn’t a miracle-worker, meaning it can’t fix underlying mechanical problems. We recommend flushing your engine a couple times for maximum effectiveness.


  65. Has Amsoil Engine and Transmission Flush shown to unstick rings/clean the undersized oil passages in the pistons on the 2AZ-FE engines and reduce any of the oil burning issues these engines were plagued with?

    1. Hi Thomas,

      AMSOIL Engine & Transmission Flush hasn’t been tested in this engine specifically, but testing in other engines has shown its ability to clean sludge from engine components. Its potent detergent system should also help free stuck rings, resulting in reduced oil consumption. If you suspect issues with your engine, try flushing it a couple of times for maximum cleanliness.


  66. I have 2014 Chevy Cruze 1.4l with turbo 64k miles. I got car at about 30k been running synthetic most of my ownership and changing before oil life monitoring says about 10% left. Is it safe to run flush on turbo engines. Oil fairly clean at changes. Thanks.

    1. Hi James,

      Yes, it’s perfectly safe to use AMSOIL Engine and Transmission Flush in turbocharged engines. Just follow the guidelines on the bottle.



  67. Hi, I have a 2015 Nissan Juke, that’s spuddering at idle 79kmiles. Dealer says engine needs replacing because of sludge. I can’t afford to replace engine, what your advice for using your product?

    1. Hi Nichole,

      Engine sludge can be caused by a number of factors, including abnormal engine operating conditions, internal engine coolant leaks and improper oil change practices (keeping engine oil in longer than what is recommended by the vehicle manufacturer or the engine-oil manufacturer). Since your vehicle may still be covered under the powertrain warranty, it’s important to provide your maintenance records, including oil-change records, to the vehicle dealership and inquire about the powertrain warranty. If you have been complying with the vehicle manufacturer’s maintenance requirements that are specific to oil-change intervals, then it is possible that a mechanical issue including (not limited to) an abnormal operating condition or internal engine coolant leak could be the cause of the engine sludge.

      AMSOIL products are not warranted for vehicles that have known mechanical issues or engines that have known sludge unless the engine has been repaired and the cause of the sludge has been corrected.

      Thanks for reading.

    2. Hi Nichole. Just a thought about your sputtering issue. If by sputtering you mean RPMs dropping low to around 500 while idling then try having the idle adjusted at a repair shop who has a capable scan tool. I’ve recently had a 2014 Just come through the shop with low idling/sputter issue and was able to increase idle RPM using Matco Maximus 2 scan tool and that took care of the issue…Hope this helps

  68. I would strongly recommend that anyone doing an engine flush with AMSOil or any other solvent based product, that you drain the oil as quickly as possible after engine shutdown. Always remember, it takes heat for the product to really do it’s work, and as soon as you let the oil cool, you will see it redeposit the suspended sludge it just loosened right back into your engine. It only makes your problems worse. (hint – get an ove’-glove and keep your hand free from the oil flow as much as you possibly can)

    1. Hi Delta Bravo,

      Just a couple things to add:
      1) You win for coolest screen name.
      2) AMSOIL Engine & Transmission Flush, for the record, is detergent-based, not solvent-based.

      Thanks for reading,


    2. By definition, a solvent is “able to dissolve other substances.” Naptha is a chemical solvent. I stand by my statement.

  69. I have a 2012 Dodge Ram Hemi 5.7 that I purchased from a salvage yard that has under 90K on it. AS following common practices I have removed the pan, valve covers, intake, front/rear seals and water pump to replace the vital seals and components. The removing the pan I noted grit in the bottom on the pan but the heads were clean. In this case you recommend flushing the engine with your project or just perform an oil change after a couple days of putting the engine in the truck

    1. Hi Yulonda,

      We can’t answer that given the limited information we have to work with. If no shop will touch it, I suspect a flush isn’t going to do you any good.

      Thanks for reading,


  70. 2000 325ci with 240k miles on it bought it 7 months ago and I opened the oil cap and it’s sludged up, what should I do?

  71. I have a 2005 Lincoln Town car and she is mint. I only use synthetic oil and change the oil every 9,000 to 10,000 miles. Is it necessary to do a engine flush with synthetic oil compared to regular oil. I have had my mechanic flush my engine twice in 6 years and she runs like a top, absolutely no problems. I bought the car in 2012 and flushed the engine because I did not know the maintenance schedule of the other owner and then only using synthetic oil I flushed it again 5 years later…….can I keep this way of maintenance or is a flush every 5 years with synthetic oil over kill? Thanks for any help you can give me…..again the car runs great!!!!

  72. Yes, engine flush is good as it is important for engine oil. Generally, an engine flush washes the gunk out of your car’s engine. In an engine flush, a technician takes out some of the oil and adds a flush additive. In your blog you give the clear idea that whether engine flush is good or bad. It is better that you can ask for the expert.

    1. And I heard people said after flush will have some engine flush left inside engine and that not good for engine, that why manufacturer not recommended the enigne flush?

    2. Hi Erik,

      It’s true that during an oil change some of the old oil remains in the engine, but the amount is minimal. AMSOIL designed its Engine and Transmission Flush with that in mind, and we have conducted significant testing to ensure it is both effective and safe for the recommended applications. You can use it with confidence.



    3. Hi Erik,

      Add AMSOIL Engine & Transmission Flush to the oil already in your engine. There’s no need to change the oil first.



  73. Hi there. I recently had my oil changed in my 2016 Kia Sorento. The dealership neglected to tighten the oil filter and over the next three days unbeknownst to me the oil drained out. When I saw my oil pressure light come on I wasn’t sure exactly what to do. I drove for maybe another 30 seconds and then pulled over. After discovering the problem and refilling with 4.5L of 5W30, I carried on as normal. My daughter said that I should get my engine flushed as there could now be small pieces of metal floating in the new oil as a result of the loss of oil. I have already told the dealership what happened and they accept responsibility but said nothing about an engine flush. Should this be pursued?

    1. Hi Brenda,

      Since the dealership made the mistake and accepted responsibility, I’d let them handle it. They should do whatever is required to get your vehicle back up and running properly. If your car acts up, just be sure to take it back immediately.

      Thanks for reading.

  74. I have 150,000 miles on 2007 Toyota sienna LTD. Dealer told me that the engine is sludged. Would cost $5000 to clean.

    I tried Seafoam. And I’m getting oil changed as we speak.

    Will it be safe to use your product now? Do you think it will make a difference?

    Can I add it after the oil is changed and drive with it inside until my next oil change?

    1. Hi Chelley,

      We recommend having the engine cleaned before using our product. While it will help to clean out the engine, the concern is still with the potential for existing debris in the engine plugging the oil pick up tube. Was the dealership able to identify what was contaminating the oil causing the sludge build up?

  75. Hello, I have a 2006 Sierra 2500hd with the duramax engine. The truck has 430k on it. Recently I dropped the lower oil pan and to my surprise tgere was no caked on sludge in it. My question is do you think I might benefit in using the engine flush? Or do you think with that many miles I may do more harm than good? I change the oil every 10k miles.

    1. Oh I forgot to mention I use your bypass oil filter kit. I’ve has that since about 350k miles

    2. Hi Tad,

      It definitely wouldn’t do any harm, as it is a detergent based cleaner, not solvent-based. It probably wouldn’t hurt with that many miles on it, in case there’s any buildup in the top end of the engine, but it sounds like this one is very clean.

      Thanks for reading.

  76. I inherited a 1983 Mercedes diesel , 206000 miles, that smokes a fair amount. The oil was usually changed every 3000 to 5000 miles. The engine needs some work, but it sounds that the engine flush might be a good thing to do for this one. Does the engine flush work on all engines or is there a special flush for diesels?

    1. Hi Greg,

      AMSOIL Engine & Transmission Flush is recommended for gas and diesel engines, so it’ll work fine in your Mercedes.


  77. Would this adversely affect the clutches in my Yamaha xv1900 Raider? I have 109,000 miles on my bike and have used 20/50 Amsoil since my second oil change which was around 6,000 miles. I put new clutch plates in there at around 80,000 just cause I thought it was due. Everything in there was spotless. I have started to notice a little faint ticking lately and was wondering if this product or one such as Marvels Mystery might help the problem.

    1. Hi Ron,

      AMSOIL Engine and Transmission Flush is not recommended for use in wet-clutch-equipped motorcycles and other powersports equipment. We do not recommend oil additives, such as Marvel Mystery Oil.

  78. I have a “97” Civic with 180k miles on it, I’ve had it for 2yrs now, I add about a half a quart of trans fluid in the engine n drive it for a 100 miles n then change my oil afterwards, I use Valvoline 20\50 (people who know use Valvoline ) because of of the high milage, it used to use a quart of oil a month until I switched to 20\50, I haven’t had to add oil since! I’ve been doing this for many years n had have great results from it, the trans oil is a high detergent n cleans the internal engine parts gradually, rather than all at once possibly damaging the engine, my uncle uncle use to use diesel fuel to flush out his engine, for some reason I didn’t like the idea or the smell it created! I’ve had many cars n have done this to all of them resulting in very high mileage, its very inexpensive n a lot easier to use! Wat do u think of this?

    1. Hi Danny,

      Switching to a higher viscosity can sometimes reduce oil consumption since the thicker oil does a better job sealing worn rings or valve guides. This could certainly be the case with your Civic after switching to 20W-50. Also, thicker oils (and synthetics) typically have reduced volatility, meaning they’re more resilient to evaporation at high temperatures.

      As for adding transmission fluid to the oil, I’m not going to tell you what to do – it sounds like you have plenty of experience working on cars.

      But I will tell you why I wouldn’t do it.

      1) The detergency, or cleaning power, of ATF is much less than motor oil. ATF doesn’t see the combustion byproducts or contaminants like motor oils do, so they are designed with much less detergency. So, in most cases, adding ATF to motor oil actually reduces cleaning power. Instead, ATFs have elevated levels of friction modifiers and other additives that help with protecting gears and clutches.
      2) ATF can disrupt the engine oil formulation and reduce its effectiveness. A good motor oil is a fine balance of base oils and additives that are designed to work together to fight wear, reduce friction, prevent deposits and provide cleaning power. Adding a foreign substance to the oil – tranny fluid, diesel fuel, an aftermarket oil additive – will throw off oil chemistry and possibly negatively affect wear protection, oil life or more. You may see a benefit in one area, but at what expense?
      3) ATF can alter the viscosity of the oil, reducing wear protection. This likely isn’t an issue in your case since you’re running a higher-viscosity oil than what the engine manufacture recommends.

      A good motor oil contains enough detergents to prevent sludge in clean engines and slowly dissolve accumulated sludge in older engines. The cleaning power of motor oil is designed to work gradually over subsequent oil changes and not necessarily all at once. Plus, our Engine & Transmission Flush is specifically designed to clean sludge, whereas ATF isn’t designed to be used in an engine.

      My two cents. Thanks for reading.

  79. My 02 sierra has 256,000 miles on it! It’s starting to loose oil pressure once it gets hot and under a heavy load causing lifters to tap. I’m thinking the strainer is picking up gunk. If I run a flush thru it should I go back with an engine restore product ?

    1. Hi Jody,

      Engine restore product? We don’t recommend using aftermarket oil additives. Check out this post to find out why.

      If you suspect “gunk” has accumulated in your engine, AMSOIL Engine & Transmission Fluid may help you, so you can feel safe giving it a try.


  80. Aside from the 2 Toyota dealer provided oil changes I have used Amsoil. Oil change interval 10,000 miles. My next oil change will be at 60,000. Would using the Amsoil flush be recommended on my 2010 Prius? And, if so, could an oil analysis be run at the same time?

    1. Hi Michael,

      Sure, you can use AMSOIL Engine and Transmission Flush on your Prius. And you can certainly perform oil analysis. To get the most bang for your buck, however, I suggest you perform the oil analysis first before using Engine and Transmission Flush and changing your oil. The report may come back saying your oil is suitable for continued use. No sense changing it if it’s still performing well.

      Thanks for reading,


  81. Hi,
    I purchased a 2002 Sierra with a 5.3 liter a few months ago and now that the temps are colder it appears to have the cold engine knock for about the first 30 seconds. One GM statement says that this is from build up above the piston seal. Do you think a flush will help?

    1. Hi Sierra Dan,

      I reached out to our Technical Services Department, and here’s what they said:

      As temperatures drop, the oil thickens. This means it takes a little longer for it to circulate on initial startup, and build up pressure and completely circulate through the engine. It has nothing to do with piston sealing. Another occasional cause is if the oil filter is mount so the oil can flow out when the engine is shut off, and the anti-drain back valve is not working properly, it can mean it takes longer to refill the filter and then circulate through the engine. Changing the filter will correct this problem.

      I hope that helps. If you need more info, contact them at [email protected] or 715-399-TECH.


    2. Cold knock on those GM Truck engines is caused by carbon build-up on the piston above the rings. An oil additive is less likely to reach that area than a fuel additive like AMSOIL PI. I would try running a couple tanks of fuel with PI in it and see if that helps. A mild cold knock on these engines is usually harmless too.

  82. Does Amsoil recommend using the flush occasionally even on strictly Amsoil Signature run engines? I only go 10,000 between changes but its severe service…lots of short trips in winter. Thanks!

    1. Hi John,

      No, we don’t. It’s strictly up to you. If you’ve used Signature Series exclusively, there’s likely not much that needs cleaning. However, you’re safe to use it between oil changes if you want to go that extra mile.


  83. Hi AMSOIL, my car has about 16,600 miles and I am the original owner. I have my oil and filter changed every 7,500 miles per maintenance schedule. When should I start using engine flush and how often should I use? Thanks.

    1. Hi,

      Per our product recommendations, flushing your engine isn’t required when using AMSOIL products. But, if you want the peace of mind that comes from doing a little house cleaning every so often, you can use AMSOIL Engine and Transmission Flush as often as you feel comfortable with it.


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