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What happens if you mix different engine oils?
Have you ever topped up your engine and realized afterward that you used a different type of oil?
It’s a common situation. And no, your engine won’t fail because of it.
But what actually happens when you mix different oils? And is it something you should keep doing?
Let’s clear up all the confusions once and for all.
When you pour two different oils into one engine, a few things happen inside the crankcase:
In short, it works, but not well. The mix won’t damage your engine immediately, but it won’t deliver consistent protection either.
Even mixing two full synthetic oils (like AMSOIL and another brand) isn’t ideal. While it won’t cause mechanical failure, every manufacturer uses unique base stocks and additive chemistries. When you blend them, you lose the engineered balance that gives synthetic oil its edge.
That means:
To get the full benefit of synthetic technology, stick with one trusted brand throughout the oil’s service life.
Professionals and performance drivers prefer AMSOIL Signature Series Synthetic Motor Oil, designed for long-lasting protection, extended drain intervals, and stable viscosity in all temperatures.
If you accidentally mix 5W-30 and 10W-40, your car will still run, but it’s not optimal.
Viscosity determines how easily oil flows at different temperatures.
When mixed, the resulting oil can be unpredictable:
Modern engines rely on precise lubrication to run smoothly and protect every moving part. Today’s engines are built with tight tolerances, advanced materials, and complex systems that need the right thickness of oil to work properly.
That’s why manufacturers specify exact viscosity grades. They want to make sure the oil flows correctly when the engine is cold and still provides strong protection when it’s hot.
So, using a consistent, high-quality synthetic oil helps maintain this balance, reduces wear, improves performance, and keeps the engine healthy for the long run.
Mixing different oils doesn’t cause instant damage. But over time, it compromises performance.
Here’s what you risk:
Engines are more advanced and tightly engineered than ever. To get the protection they’re built for, consistency matters.
If your goal is smoother performance, fewer oil changes, and a longer engine life, don’t mix. Choose one premium synthetic oil and stay with it.
Instead of mixing oils, use a full synthetic that performs across all driving conditions.
AMSOIL is formulated with advanced synthetic base stocks and proprietary additives to deliver consistent protection, no matter the climate or driving style.
Here’s what sets AMSOIL apart:
Whether you drive in freezing Canadian winters or hot U.S. summers, AMSOIL keeps your engine protected and running at peak efficiency, without the uncertainty of mixed oils.
Can I mix synthetic and conventional oil in an emergency?
Yes, it’s safe short-term. Just replace it with a full synthetic oil at your next change.
Can I top off with synthetic oil if my car uses conventional oil?
You can, but performance will match the weaker oil type.
Can I mix two synthetic oils from different brands?
Yes, but it’s best to avoid it; the additives are balanced for specific formulations.
Will mixing oils void my warranty?
If the final blend meets your manufacturer’s API or ILSAC specifications, your warranty stays valid. But for reliability, it’s better to use a single brand and viscosity.
Mixing different engine oils won’t destroy your engine, but it does reduce performance and protection.
If you care about long-term reliability, better fuel economy, and fewer oil changes, the solution is simple: use one trusted, high-performance synthetic oil.
That’s why more drivers across the U.S. and Canada rely on AMSOIL Synthetic Motor Oils, engineered to outperform, protect longer, and give you peace of mind every time you start your engine.
