How Do I Switch from Conventional to Synthetic Oil?

To borrow a famous slogan, just do it.

There is still some confusion about changing to a different type of oil in vehicles, particularly older models that have accumulated many miles. A small group of ill-informed individuals in garages and on blogs still cling to old beliefs that synthetic motor oils cause roller followers to “slip or skid,” or that switching to synthetic motor oil causes issues in older engines, particularly oil leaks.

Facts have since replaced these outdated ideas about synthetics causing engine problems.

The use of synthetic lubricants is growing rapidly because properly formulated synthetics offer benefits well beyond what conventional and synthetic-blend products provide. Many new passenger car and light truck vehicles come factory filled with synthetic lubricants – not just high-performance sports cars.

checking your engine oil dipstickThere are a couple ways to switch to synthetic motor oil for the first time.

• Jump right in and simply change the oil. Take your vehicle to your mechanic or the nearest quick lube and ask for synthetic motor oil. Or, dust off your drain pan and do it yourself. You don’t have to do anything special to your engine first, and the synthetic oil isn’t going to cause problems in your vehicle that weren’t already there.

• Flush the engine first. Though not required, an engine flush more immediately removes sludge and debris accumulated over time.

The main difference between flushing your engine and a normal oil change to synthetics is the rate at which the built-up debris is removed from older engines. If you change to AMSOIL synthetic motor oil without flushing, for example, the detergents in the motor oil will clean accumulated deposits from the engine over subsequent oil changes. When you use AMSOIL Engine and Transmission Flush, the cleanup is more immediate and helps ensure the engine is clean and free of any accumulated contaminants.

Wondering if an engine flush is right for your vehicle? Find out here.

However, we recommend using AMSOIL Engine and Transmission Flush if you want to give your engine a fresh start before switching to synthetic motor oil.

Ready to make the switch to synthetic motor oil? Check out our Product Guide for the right oil for your vehicle.



  1. I put synthetic oil in my high milage engine (around 350,000 kms) and it almost immediately leaked like a sieve. Drained it and replaced it with natural oil and some seal conditioner which helped slow the leaking. It now has 595,000 kms.


    I have a similarly old manual transmission that needs an oil change. Natural oil is very hard to find, and I do not want to tear the tranny apart and replace all the seals and clutch if is starts leaking.

    Any advice?

    1. Hi Bob,

      My inclination is to ask why it’s so difficult to find conventional manual transmission fluid anymore (or automatic transmission fluid, for that matter)? It’s because automakers are increasingly using and recommending synthetic fluids. My intuition is to trust the automakers and their research, and assume synthetic fluid will work just fine in your application. However, I understand your reluctance based on past experience. My advice is to search online; I suspect you can find conventional fluid available through an online retailer somewhere.

      Best of luck,


  2. Safe flush.

    It’s detergent based, with a likely heavy dose of esters of the fast acting variety, rather than solvent based.

    Big thumbs up from me.

    Kinda like a quickie version of Valvoline PB Restore.

  3. I had a f-150 5.4 v-8 I got used @124,xxx highway miles. I always used the reg oil it called for, one oil change I switched up to synthetic ( was not Amsoil) in the first 5 miles I noticed it seemed a little sluggish the next day you could really tell it wasn’t happy with the change. I changed it back to what was always used and everything was fine. Yes everything was flushed cleaned and changed that day. I’ve never used Amsoil in my truck or cars.However I use in all of my dirt bikes,quads,snowmobiles, and it’s always been great and you could definitely tell a difference after an oil change. I love the product so much I became an Amsoil dealer. I’ve been using Amsoil since 1992/93,and still do to this day. I don’t have any at s at the moment but I’ve got 20 quarts on hand and ready to go! ( just an experience I had and again Amsoil was not the oil put int the truck.

    1. Good information well explained good to kno about the procedure how to do it thank you very much it very helpful very supportive learn something new today

    2. I’ve been a Dealer since 1987 and use it in everything and I have not had any issues with AMSOIL plus I change my oil once a year and the engine inside still looks like new.

  4. I have a 1996 Harley Davidson FLSTC with 8,000 mi. I need And oil and a chrome filter if you have one. Which oil , how much, and filter #.

    1. Hi Walter,

      Two things:

      1) I’m jealous. A ’65 Mustang is my dream car.
      2) For that, contact AMSOIL Technical Services at [email protected] or 715-399-TECH and they’ll gladly help you.


  5. Great article. I still hear people say Synthetics make your engine leak or they are thinner (that’s the strangest) and the one thing I hear the most is “you can’t switch back once you use synthetic oil”. All these myths have lingered for so long and are slow to die.. Still even after I explain viscosity is viscosity no matter the type oil, or the cleansing effect of detergents, some still persist in believing these old tales, and with some the light turns on and I have a new customer.
    I persist in using and promoting the benefits of Amsoil and articles like these are a great help.

  6. Flush the engine and press on. I have used amsoil for a number of years. More than 20. It is expensive (I hate the word cheap) BUT the bottom line the gas milage improves and oil usage decreases. I love it when I just slip it off the grip stick and it just feels slicker. Try that after 6K with mobile 1. I’ve used it on Honda’s and Jeeps completely (trans, differentials, transfers) and never had a failure. My mechnicics just step back and nod. I tend to be just a little aggressive (not crazy but my wife is confidence when the snow or sand is deep and the laughter is high)
    on my jeep vehicles ( especially in 4W).

    1. Hi Al,

      We’re happy to hear about your great results using AMSOIL products. Thanks for sharing.

  7. This is a good product. I am using this AMSOIL product long time and my car engine is always a good condition for This product. Thank you for this information.

  8. 1. rebuilt 65 mustang, 289 engine – has 7000 miles – 10w30 oil – should I CHANGE to 10w30 syn. amsoil oil?
    2. should we flush out engine, before switching to synthetic 10w30 amsoil?

    Thanks for Ur reply & help info.

    1. Your engine should not require flushing because it hasn’t ran enough to accumulate sufficient “motor sludge”. With only 7000 miles you can switch with your next oil change and greatly increase the life of your motor if used consistently vs conventional oil.

Leave a Reply