JPS

With all the discussion over the years about Brad Penn vs Mobil 1 and others...can you mix? Add a quart or two of one if you are using the other? Not sure I see why not, but...?

Someone asked me and I don't know. Figured you guys would.

No HTwo O

Why? For what purpose? Buy the right oil and the right viscosity, and be done with it. Do UOA's to support your choices and track your engines health over time.

Now, if you have a spare (unopened) quart or 2 hanging around the garage and want to use it up, that might be fine. But it is usually not advisable to mix different brands (different detergent packages for one). It's more common to mix oils of the same brand, for example 5 quarts of Mobil V-Twin with 5 quarts of Mobil 15W50.

JPS

Long story short someone said they were going to change the oil and didn't. Think Mobil, but I have BP on me.

NC TRACKRAT

I would not mix brands unless it were a dire emergency. OK to mix wts. of the same brand and type. BP is a semi-synthetic. MOBIL 1 is full synthetic. Before they came out with their 15W40, BP said it was o.k. to mix 10W30 and 20W50 to arrive at 15W40.

certz

I mix BP weights to come up with an appropriate winter weight and was told to do this by LN Engineering - I cannot remember the two weights I use off the top of my head, though. I would not mix brands, though, as said above.

Steve Weiner-Rennsport Systems

++1 Precisely!

2Many Cars

My understanding that mixing brands is risky because each brand uses slightly different additives and some of the additives may not play well together. I'm sure it's not a problem with all combinations but why take the chance if you don't have to.

JPS

BP was all I had. I'll change the oil when I'm back from the weekend. Advice makes sense.

Kika

I just switched to BP at my last oil change, and while we completely drained the case, I would think that there are a few quarts of M1 still floating around in there. So I am thinking that upon changing brands, it is impossible NOT to have some mixing.

thoughts?

stickypatch

Exactly what I was thinking. Having looked through the oil change DIYs, I seem to recall only 9 quarts are changed of the 12 quart capacity.

Kika

We put 10qts of BP in,so there has to be a few M1 qts floating around. I have my suspicions that concerns are vastly overblown.

Rust911

Actually had a similar problem....bought a '96 993 last year from a dealer and after 3k miles looks like Im a bit short of oil, problem is the only record I have of an oil change was in Sept 2011 when it looks like the previous owner used Swepco 306 15-40W (non synth)...i need to top it off but not 100% sure oil was changed again between old owner and dealer, and ordering Swepco online will take a week or so. So in the mean time I was considering toping off with another non-synth 15-40W brand. For the love of the car, keep your records and turn in when you sell

M. Schneider

As an aside, what's less than ideal about the factories Mobil 1 fill?
At what piont does high concentrations of ADDP zinc fomulated oil harm the cat's?

Steve Weiner-Rennsport Systems

Mike,....thats a good question.

I've replaced cats due to overheating (too lean/ too rich fuel mixtures) and/or oil contamination (overfilling), but after all these years, I've never had to replace a cat due to Zinc poisoning. Perhaps Dealers or other shops who do more street car maintenance have done so.

As an educated guess, I'd say something around 1800ppm for ZDDP, however there are other factors at work such as how the car is driven.

What I would tell you is to check the pricing on a new pair of cats against camshafts, rocker arms, and the associated labor to replace them. Further, there are other engine components that do not last as long using a reduced ZDDP lubricant.

Bill Verburg

You do realize that whenever you change oil you are mixing some old oil w/ the new, unless you drain the lines and coolers which is rarely done.

M! is designed to be compatible w/ all dino oils and I've never heard of an issue the resulted from commingling the different types.

zinc poisening of the cats is a long term effect that only arose when the manufacturer had to provide very long term emissions warrenties