Can I Mix Synthetic and Conventional Oil?

While it's safe to mix synthetic and conventional oil since they're compatible, it's not a great idea. Here's why you...

July 15, 2020

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.

More like this