Mixing different viscosities

[ChrisJ]

I just wanted to share a small bit of info I just received from Mobil via email.
According to them there is no harm in mixing different viscosity oils. For example adding a quart of 5W30 to your engine when you had used 0W30 or 10W30 when you changed the oil.

In the past I have run 0W30 and sometimes you can't find that so its nice to know there is no harm in mixing them. Of course, I would personally try to keep the second number the same. Obviously adding a quart of 0w30 to 4 quarts of 10w30 will thin it slightly in cold temperatures where adding a quart of 10w30 to 4 quarts of 0w30 will thicken it slightly in cold temperatures.

The original reason I had emailed them was I changed the oil in my generator using 10w30 M1 extended performance and ended up a hair short. I had 5w30 M1 extended performance on hand so just topped off with that. Obviously the generator doesn't care if it has 0w30, 5w30 or 10w30 but I wanted to be sure there wasn't some kind of chemical disaster waiting to happen.

 

[sx sonic]

This will be very helpful to a good number of people.

That said I've long been stating that mixing viscosities is fine, with one caveat. That the different weight oils yield a weight that is acceptable for the application and also both fluids are intended for the same purpose.

 

[vento]

I just wish it was easier to actually fill out the 4.8 quarts? or whatever it is they want us to put in our engine... I usually end up going 4.5 quarts and call it a day.

What would be the benefit of using 0w30 over 5w30? I understand its less viscous, but are the tolerances of our cars tight enough to make use of it?

 

[ChrisJ]

I just wish it was easier to actually fill out the 4.8 quarts? or whatever it is they want us to put in our engine... I usually end up going 4.5 quarts and call it a day.

What would be the benefit of using 0w30 over 5w30? I understand its less viscous, but are the tolerances of our cars tight enough to make use of it?

0w30, 5w30 and 10w30 all behave like 30 weight oil at operating temperature. The difference is the lower the first number, the closer it stays to the proper viscosity as it cools. As others will tell you 0w30 isn't really necessary unless you see really cold temperatures often (-20F). However, 0w30 is already noticeably thinner at 100F compared to 5w30 so even if your engine sees 10-20F often 0w30 will be beneficial in my opinion.

This thread really wasn't intended to push 0w30 although I do prefer it. It was just to let others know mixing 0w30, 5w30 and 10w30 is harmless and can be done without concern under many conditions. If your Sonic has 5w30 in it and for some reason you're low and can only find 0w30 or 10w30 then by all means add it without concern.

As for getting the level right, I just buy 5 quart jugs and add it until I have a certain amount left, then I know I'm good. I hold onto that little bit until the next change when I dump my old oil into that jug and hold onto the new one. Then I take a bunch of 5 qt jugs at once and dump them out at the local parts store.

 

[trollbait]

It doesn't have to be real cold out for the 0w- oil to be thinner, and thus better, during start up. There is a gap between the 0w and 5w actual measured viscosity with the 'cold' test. That test is at 40c, or 104f. As it gets colder that gap will widen.

 

[vento]

Its usually between 1-15 Farenheit around me in the winter. Ill probably stick with the 5W for now. Good to know I can use others in a pinch though.

 

[MartyH]

Yes, mixing weights is fine. I'm running 5w30 Dexos 1 compatible oil in the Midwest. I'm using the same weight and brand each time, Warren Oil's Mag1 Dexos 1 just to support an oil company other than the largest.