Can I Mix Synthetic and Conventional Oil?

While it's safe to mix synthetic and conventional oil since they're compatible, here's why it's best to avoid it.

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AMSOIL Synthetic Motor Oil
author John Baker
by John Baker
February 17, 2022

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. In this post, we’ll also look at if it’s safe to use regular oil after synthetic oil.

Let’s take a closer look.

Can I Mix Oil Types?

With synthetic lubricants continuing to grow in popularity, the question of whether synthetic and conventional oil 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.

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.

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.

Can You Use Regular Oil After Synthetic?

Yes, it’s perfectly safe to switch to regular conventional oil after using synthetic oil. As mentioned, both oil types are made of compatible components; it’s just that the base oils and additives in the synthetic oil are higher quality.

But, since synthetic motor oil provides improved wear protection, engine cleanliness, fuel efficiency and other benefits, why would you want to use regular oil again?

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by John Baker

AMSOIL Technical Writer and 12-year veteran of the synthetic lubricants industry. Enjoy making complex topics in the automotive, powersports, industrial and other markets understandable. Avid DIYer who always seeks to repair rather than replace.

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AMSOIL Synthetic Motor Oil

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