Any REAL danger of mixing oils?
 

I changed oil on my car with Rotella W15-40. I'm just about 1/2 quart short, and I happen to have some generic W20-50 around. Any danger of putting that stuff in?

jeff 1991 300d, 131k

don't put it in unless it is diesel rated oil.

Danger? Not really. There is also no danger in running 1/2 quart low, fill it when you buy more oil.

I doubt if 1/2 quart would make any difference. But, I do not think it is a good idea to mix any of the multiviscosity oils especially if they are different viscosities.

I do not think it is a good idea to mix different companies multiviscousity oils that even if they are the same viscosity either. As, I believe the different companies may use different set of chemicals to achieve their pour points.

But, I am cautious because do not have enough knowledge about it.

In fact out here in S. CA I use single viscosity oil. There is no problem caused by pouring 20wt into 30wt except that it is no longer 30wt; you end up with something thinner and in between.

There's no real danger, but it's preferable to top off with the oil that you already have in there. That way you don't start affecting the oil's properties.

I'd drive it as is to the store and get another gallon.

Don't even bother with a 1/2 quart. The engines usually run better and consume/leak less oil when its about half way between the two dipstick marks.

I probably would be shouted at for writing this. I think people are paranoid. I mix it all the time, w10-30, w5-40 etc to my gas cars and diesel cars and it never gives me problem. If the car is a precision instrument like a watch then I probably would not do it. But MBZ engine is built tough and can take abuse within reasons. It may shorten the engine life by 1k miles out of 500K, I would still be very happy with 499K.

One thing I never short changed myself is the interval. I always change the oil between 3k-4k miles.

Just a warning: Richard Pryor did it and he caught on fire! :eek:

No danger. But don't bother if you're 1/2 a quart down. Wait until you can use the whole quart, then you won't have to find another way to get rid of it. As someone else said, make sure it has a diesel rating... it should say something like SF/CD (I don't remember what the letters are up to anymore...) the Sx/Cx means S for spark ignition engines, C for compression ignition (diesel). The x part is the specific specification, they keep getting higher and higher as engine technology demands more of the oil. Some oils are only Sx rated, these should be avoided in a diesel. Although even then, one quart out of seven probably won't hurt, especially if you are coming up on an oil change soon. Then again, running one quart low out of seven won't hurt anything either.

The additives in different oils will interfere with each other. There is no danger to the engine, but just dont do it unless you really have to.

I do not believe this to be true. Do you have any further information on this?

That's EXACTLY what I was thinking
 

Yeah, that's what I was thinking. The car will probably never know the difference. It's only 1/2 quart out of 7 quarts, that's 1/14 of the total. Not going to ruin the entire engine for a few thousand miles of oil.

Thanks,

jeff

It goes along the same lines as "pick one oil and stick with it."

Mixing won't kill the engine but its not good for it.

All I can say is....I wouldn't do it. Spare oil laying around can always be used in the lawnmower! I think I've used 3-4 different weights and types in our 5.5 briggs mower. :D Currently its using a leftover quart of M1 Turbo diesel and truck...seems to like it! :D Next up is some 5w30 castrol synthetic....