Can I Mix Synthetic and Conventional Oil?

Yes. There is no danger mixing synthetic and conventional motor oil. However, conventional oil will detract from the superior performance of synthetic oil and reduce its benefits.

Let’s take a closer look.

Can I mix oil types?

Can I mix oil types?

With synthetic lubricants continuing to grow in popularity, the question of whether synthetics and conventional oils can be safely mixed often arises.

I’m guilty of having mixed different types of motor oil with reckless abandon back in the day. A dash of synthetic blend to top-off my Buick Century one month and a shot of cheap conventional oil the next.

While oil performance probably suffered, my engine always remained in one piece.

That’s because you can safely mix synthetic and conventional oil. In fact, synthetic-blend motor oil is simply conventional and synthetic oil already mixed for you.

But, barring an emergency, it’s not a great idea to mix oil types.

Pouring AMSOIL XL Oil into engine.

Why it’s not a great idea to mix synthetic and conventional oil

All motor oil, whether synthetic or conventional, is a combination of base oils and additives.

Synthetic base oils are manufactured using a process that removes the impurities inherent to conventional base oils. Synthetics typically contain higher-quality additives, too.

So, in the end, conventional and synthetic oils are comprised of the same, compatible components – it’s just that the components in synthetics are much higher quality.

While you can safely mix synthetic and conventional oils, you’re doing nothing more than diluting the performance of the synthetic oil.

Find out how to switch from conventional oil to synthetic.

What if you have to mix oil types?

You may not have a choice to mix the two in some cases.

If you’re traveling, for example, and suddenly find your engine low on oil, cheap conventional oil may be the only option at the gas station alongside the highway.

While it’s safe to top-off an engine that normally uses AMSOIL synthetic motor oil with conventional oil, we recommend changing the oil at your earliest convenience. In fact, AMSOIL does not support extended drain intervals where oils have been mixed.

When you’re using the best oil available, why add anything to it?

AMSOIL Signature Series

Updated. Originally Published April 13, 2015.


  1. Actually all conventional oil is going to synthetic blend. Mixture of conventional and synthetic.

  2. I currently have an older skidoo mineral oil in my unit. (Skandic) It’s a pao based oil. It’s OEM for the year (2003) but of course is no longer made other than the small supply I have on hand. Is the amsoil severe gear (75w140) compatible with this BRP pao base oil or would I need to do a full oil swap to ensure no tarring etc.

    1. Hi Marcus,

      SEVERE GEAR is compatible with synthetic (PAO) and mineral oils; however, for best performance we recommend trying to remove as much of the old fluid as possible before switching to AMSOIL.



  3. It’s a great Oil I use ever, I’m using it more than 1 year, it really works great.

    Highly recommend for every vehicle owner.

  4. Wow lots of dumb questions I hope I don’t sound stupid but have posed this question to auto parts oil reps and they can’t give me strait answer. Ok there are about 5 syn oil base stock which one is best to worst and why and what brands types there are no labels on oil bottles.

  5. One reason could be that the synthetic “eats up” the gaskets and other components. Regular oil does not have that ability and actually the debri it produces helps the sealing of the engine from oil leaks. This is generally stated to be the case for older engines. Your car is pretty new and that should not be the issue; it is doubtful, but it may be also possible that your engine was not built specifically with synthetic in mind.

    1. Hi VK,

      I’m not sure why you think synthetics “eat up” gaskets and other components, but it’s not true. Synthetics pose no harm to gaskets, seals or other components. If it were true, would automakers increasingly recommend synthetics in their vehicles? Also, while engines are designed with a specific viscosity of oil in mind, they aren’t built to use a specific type of oil (e.g. conventional or synthetic).



    2. Synthetic oils most certainly do not “eat up” gaskets and other components, maybe try changing the oil once in a while, that seems to be the problem here.

    1. Hi Paula,

      It depends. What does the manufacturer recommend regarding maintenance and the type of lubricant to use?


    1. Hi Joseph,

      By “SxS,” I assume you mean side-by-side, or UTV. If so, yes, you can use synthetic oil. Check out our Product Guide for the correct AMSOIL synthetic lubricants for your machine.



    1. Hi Ronald,

      Yes. Make sure to use the correct viscosity, however. And make sure the oil is recommended for the performance specs listed in your owner’s manual.



  6. I was using a synthetic blend but switched to a full synthetic oil in my 2008 Honda Odyssey that has 150K miles. Since I’ve switched I have to closely watch my oil level as I usually have to add a half quart every 2 weeks. I don’t see any oil leaks on my engine or driveway.
    Why did this happen after switching to a full synthetic?

  7. I switched to synthetic in my 2015 Silverado 3500 dually. Been pulling a 44′ 5th wheel raptor with regular oil with no problem. After the switch at 37000 miles I started using oil. 1 qt after about 4000 miles. I’m a little disappointed

    1. That’s easy. The problem is you’re driving a Silverado. Are you sure it’s not just leaking out of the pan like every other GM HD?

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