Is an Engine Flush Good or Bad?

To flush or not to flush.

It’s a question whose answer is obvious in the bathroom, but vigorously debated in the garage.

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 a 1980s 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.

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.

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 air-borne 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.

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.

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.engine flush

Buy AMSOIL Engine and Transmission Flush

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 you’re 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

Buy AMSOIL Engine and Transmission 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 do 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 on Jan 30, 2017


  1. 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.

  2. 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.



  3. 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.



  4. 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,


  5. 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.



  6. 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.



  7. 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.



  8. 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.



  9. 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.



  10. 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.



  11. 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.



  12. 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.

  13. 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.



  14. 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.

  15. 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,


  16. 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.

  17. 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?

  18. 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,


  19. 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.



  20. 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.


  21. 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.



  22. 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.

  23. 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.



  24. 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.



  25. 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.



  26. 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.


  27. 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.


  28. 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.



  29. 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

  30. 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.

  31. 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,


  32. 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?

  33. 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!!!!

  34. 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.



  35. 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.

  36. 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?

  37. 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. 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.

  38. 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.


  39. 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.

  40. 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.

  41. 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.


  42. 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,


  43. 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.

  44. 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.


  45. 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.


Leave a Reply