Can You Mix AMSOIL With Other Motor Oil?

You may not have a choice in rare circumstances, but here's why you shouldn't mix AMSOIL with other oil.

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AMSOIL Synthetic Motor Oil
Brad Nelson
by Brad Nelson
March 25, 2022

Using AMSOIL synthetic motor oil in your vehicle is a smart way to maximize longevity and performance. AMSOIL leads the lubrication industry by investing heavily in product research and testing. But one day you might find yourself in a pinch, like realizing your oil level is low while stopped at a remote gas station with limited options on the shelf. Let’s be honest – it’s happened to all of us. So, can you mix AMSOIL with other oil? The short answer is: “Yes, you can. But it’s not ideal.”

Mixing AMSOIL With Other Oils Dilutes The Benefits

One reason it’s not a good idea to mix AMSOIL with other oil is that AMSOIL engineers carefully formulate lubricants to protect their intended applications. Diluting AMSOIL products with other brands will reduce their benefits and potentially alter their chemistry enough to reduce protection and performance.

For example, AMSOIL Signature Series is fortified with a heavy treatment of detergent additives, helping it deliver 28% more acid-neutralizing power1 than Mobil 1,* helping engines to stay cleaner, longer. Therefore, if you dilute Signature Series with another brand, you also dilute the additives, reducing performance.

Can I Mix Conventional Oil With AMSOIL?

While performance will suffer, it will not damage your engine to add conventional motor oil to your engine.

That’s because you can safely mix synthetic and conventional oilIn 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, and the resulting blend will not support an extended oil change.

Even though 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.


Although you might know that synthetic oils outperform conventional oils, you might not understand why. The differences begin at the molecular level.

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Can I Mix Different AMSOIL Product Lines?

If, say, AMSOIL Signature Series 5W-30 Synthetic Motor Oil is installed in a vehicle, and the vehicle is later topped off with AMSOIL OE 5W-30 Synthetic Motor Oil, the vehicle will continue to operate just fine. Signature Series and OE Synthetic Motor Oil share a similar base chemistry, and formulations of the same viscosity can be safely mixed.

However, mixing the two product lines will reduce the lifespan and performance benefits of the super-premium Signature Series Synthetic Motor Oil, so we recommend against mixing different AMSOIL products.

Use In Case Of Emergency

If you are in a dire situation with a low oil level and a long distance to drive, it’s OK to add the motor oil that’s available. The resulting mix will not support an extended-drain interval and will create a need to change oil sooner than planned. But, if it’s that or your engine, choose your engine. Do what you must, then drain and restore to what’s ideal.

1Based upon independent testing of Mobil 1 Annual Protection Full Synthetic 5W-30 and AMSOIL Signature Series 5W-30 in ASTM D2896. Oils purchased July 2020.

by Brad Nelson

Brad Nelson is a staff writer for AMSOIL. Outside of work he enjoys family adventures, wilderness exploration and riding/wrenching on vintage metric motorcycles.

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AMSOIL Synthetic Motor Oil