skrapiron -FSO wrote on 07/11/08 at 21:40:58:I need the advice of you engineering types. KwakNut, if you're out there, I'd really appreciate you weighing in...
I'm fast approaching another maintenance interval on my bike. I took stock of what I have in the garage and found that at some point, I bought a bottle of Mobil1 syntethic 10w40 instead of the Mobil1 synthetic 20w50.
Will I cause any kind of compatibility problems by mixing the 2 different grade oils?
I used to add motor-honey to my Ford pickup every oil change to keep the oil consumption down. (it was a ford. the thing ate oil!) I know that motor-honey (STP oil treatment etc) is a viscosity modifier that prevents burn-off. I still had the same base oil, but with an additional additive package. No problem there.
My concern is with mixing the 2 different grade oils. Even though they are from the same manufacturer and should share the same PAO base oil, is there any potential for incompatibility between the 2 different grade oils? What about their additive packages, detergents etc? Will there be the potential for sludging, foaming or oil break-down if I blend the 2 together? I'm probably being paranoid, but at $8.00 a quart, I want to be sure before running out and getting another bottle of 20w50 and always having the orphan bottle of 10w40 hanging around......
The base stock plus the viscosity improver will yield the final weight...i.e. mix 10-40 and 20-50 and you get basically 15-45. The viscosity improver will combine oil molecules together from the base stock (the first number) to make bigger oil molecules/thicker oil. Some 20 weight may combine to 80 weight in the above example, but your overall mixture will flow like a 15-45.
I wouldn't recommend mixing oil more than 1 or 2 grades different, i.e. don't mix 5-20 with 20-50, and certainly don't mix 0-50 with straight 30! You'd end up with some ridiculously huge molecules floating around in your engine! Mixing 5 with 10 or 10 with 15 or 20 is okay (first number.)
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