Can You Mix Synthetic Oil With Regular Oil?

You’ve landed on this page because you want to know if  you can mix synthetic oil with regular oil.  So I’ll give you a quick answer…

Yes, you can.

If my simple (and correct) answer is good enough for you, you can go on with your day.  Close this window and go back to what you were doing. 

Maybe my quick answer isn’t good enough for you.

“Thanks Kevin, but my buddy said his cousin’s neighbor’s brother is a mechanic… and he said mixing synthetic with regular will turn your oil to gel and your motor will seize.”

Not true!  Your cousin’s neighbor’s brother (who happens to be a mechanic) is wrong. Mixing synthetic oil  and regular oil will do no such thing.  

If you don’t believe me and you’d like a heaping spoonful of proof for your pudding, read on….

The best place to start discussing this widely debated  topic is  synthetic blend oil. 

What is synthetic blend oil?

Quart of Valvoline durablend synthetic blend oil
Quart of Pemzoil gold synthetic oil
Quart of Mobil Super Synthetic Blend Oil

Synthetic blend oil is exactly what it sounds like. It’s a motor oil that is part conventional motor oil and part synthetic motor oil. It was created to give consumers some of the advantages of synthetic oil at a lower price point. Here’s a few examples of readily-available synthetic blend oil:

Mobil Super Synthetic Blend

Penzoil Gold Synthetic Blend

Valvoline Durablend

If three of the biggest names in motor oil are offering a blended product, then it’s pretty safe to assume that it’s OK for you to mix synthetic oil with regular oil in your car…. Regardless of what your buddy’s cousin’s neighbor’s brother says.

But should you mix synthetic oil with regular oil?

We’ve proven that mixing oil types  won’t hurt your car. But  mixing isn’t something you should do intentionally. 

To be clear: it’s OK to purchase and use pre-blended oils like the ones I mentioned above. 

What’s not OK is for you to make your own blend. 

So when it’s time for your next oil change, don’t skip over to the oil shelf at your auto part store and buy a quart of this and a quart of that…. And make your own weird concoction.

Don’t.  Just don’t. Leave the oil blending to the scientists who know what they are doing.

Topping off synthetic with conventional (and vice versa)

The only time you should blend synthetic and conventional oils on your own is if you need to top off your engine’s oil and you don’t have access to the same oil that’s currently in your car.

For example….Imagine you’re out on a road trip and you discover that your car’s oil level is dangerously low. So you stop at the nearest gas station to buy a quart. You alway use full synthetic oil in your car, but the gas station only has conventional oil on the shelf.

Not a problem! Buy the quart of conventional and add it to your engine with confidence. Oils for gasoline engines are designed to be compatible with each other. 

The reason why you shouldn’t try to make your own blend  is mainly because engine oils have all kinds of complicated additives in them. These additives do good things for your engine like help keep it clean and change the properties of oil so that its viscosity changes with temperature.

When you blend two different oils, these additives can conflict with each other and may reduce the effectiveness of all the good things they are meant to do. 

It’s important to note that the conflict between additives generally won’t cause harm to your engine…. So don’t worry about that.

Summing up, blending synthetic oil and regular oil won’t harm your motor. The downside is this: creating your own blend  may reduce some of the benefits the oils provide to your engine.  If you want to use a blended oil in your car, the smartest thing to do  is to use a  pre-blended oil off the shelf.

Penzoil platinim synthetic and Mobil super conventional under the hood of my Audi Allroad
Decisions, decisions…

Can you mix oil brands?

We’ve determined it’s OK to mix synthetic oil with regular oil when necessary. But is it OK to mix oil brands?

Yes, you can.

However, you shouldn’t do it as a regular practice for the same reasons you shouldn’t make your own blend of synthetic and conventional oils.

Whether it be two synthetic oils or two conventional oils, different manufacturers will use different additives that may conflict with each other and potentially reduce the effectiveness of said additives.

And just like we discussed with mixing synthetic and conventional oils…. mixing different  brands of the same oil type will not harm your engine either.  So mix with confidence if you must do it.

Let’s table blending oil and talk about switching. 

Can you switch from synthetic oil to regular oil?

This is a topic that has been debated for years and is still debated to this day. Many gearheads take a passionate (and misinformed) stance on it.  

I’m here to tell you, yes, you can switch from synthetic oil to regular oil.

And guess what?  You can switch back and forth as many times as your little heart desires!

Oh happy day!

YEAH, BUT, “…my buddy’s cousin’s neighbor’s brother  says….”

STOP IT! You’re buddy’s cousin and his neighbor AND HIS BROTHER are all idiots!  Stop listening to them for crying out loud!

Yes, I know… I’m just some guy on the internet who may or may not even be real. So how am I any better than the cousin’s neighbor’s brother? You have a good point here….

Time to digress. 

How about this…. The major oil companies say you can switch back and forth between synthetic and regular. Here’s a couple quotes…

From Penzoil: “This is one of the most persistent myths about synthetic oil—and completely untrue. You can switch back and forth at any time.” Click here for the statement source.

From Valvoline: “Not true. Synthetic and conventional oils are compatible, so it is not harmful if you decide to switch.” Click here for the statement source.

Valvoline and Penzoil are two of the biggest producers of engine oil. Do you really think they’d give advice that would destroy your motor? 

It might be bad for business, dontchya think?

So switch back and forth freely, my friends!


At the end of the day, your motor oil of choice should be what your car manufacturer recommends.  Period. 

And when it comes to mixing synthetic and oil and regular oil, it’s OK to do if you do if you must..

Just be careful of what people recommend. Especially your buddy’s neighbor’s brother.

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