Best of Deals Car Reviews Repair Shops Cars A-Z Radio Show

Mixing Synthetic Oil

I use full synthetic oil in my 2005 Toyota Corolla CE, I buy whatever brand is on sale at my local auto parts store. The sales come with 5 quarts, but I only need 4 quarts for an oil change. So now I have 4 individual quarts of Mobil One, Pennzoil, and Castrol. Can I mix these individual quarts to make a full oil change, or are they incompatible somehow?

Yes, if they meet the same API spec. A 2005 Toyota can use off the shelf oil and you can mix any synthetic or non synthetic oil of the right viscosity, such as 5W30.

If you own a turbocharged import, such as a VW or Benz. you need the exact oil specified for that vehicle.

All SAE motor oils are compatible with each other, they will mix without harm…But your plan is probably not the best idea…

I’d combine them, no problem.


You’re fine

Your car calls for 5w30 conventional oil, to be changed every 5000 miles

You’re using 5w30 full synthetic, which is one step better. The engine isn’t going to care that it’s a mix of Castrol, Pennzoil, etc. As long as the viscosity is correct, and you change it on schedule, you’re good to go.

And you’re smart to buy synthetic only when it’s on sale

Mobil 1 synthetic is on sale at Costco right now, by the way.

Different companies may use different Vii additives, viscosity index improvers…When you mix them, you can’t be certain what the viscosity of the mixed product is…

If you want to REALLY get into this, you can take it to Here, the true motor oil obsessives squeeze every drop out of the subject…

I can’t speak about the rest of you guys, but I’m not losing sleep over what brand of 5w30 synthetic oil OP is putting in the crankcase

Those guys on that other website can obsess all they want . . . without me

What db said. Especially because he’s exceeding requirements anyway.

While I agree, it should be noted that for some reason, some brands of synthetic don’t work as well in some cars. Using Mobil 1 (which I use) in a BMW causes higher oil consumption. Don’t know why, don’t care to.

While I agree with all that has been said, woudn’t it be a great time to treat your lawn mower, snowblower and other single quart capacity ( often) to a years use on a synthetic. So even though I agree, I don’t practice what I preach and tend to use oil from the same manufacturer…for absolutely no good reason.

@Bing I used Mobil 1 once in my wife’s 2005 Subaru Legacy turbo around 35k miles. It was the first time over 3500 miles I had to top the oil with nearly a quart. Went back to whatever wife’s mechanic and her local guys at gas station with one bay use (bulk dino) and it does not burn a drop. We have over 158k on it.