My thoughts,
* oil wedge/separation distances are related to viscosity (same speed, load, and bearing), so MMO will reduce the separation distances. (Enough to be a problem in a 20W-50 in winter, probably not).
* FM/AW additive levels will be reduced proportionally. Something that is 1000PPM becomes 900ppm with a 10% MMO brew. (Enough to be an issue in a 20W-50 which already has way more additive than any 30 can legally, probably not).
* Other additives, TBN similar to the above already noted, less additive over more oilvolume.
* Chlorinated hydrocarbons have their own advantages in boundary lubrication, and disadvantage other respects.
This case, a 20W-50 in winter, if it feels good do it...I'd have serious thought of thinning/diluting some of the thinner oils.
* oil wedge/separation distances are related to viscosity (same speed, load, and bearing), so MMO will reduce the separation distances. (Enough to be a problem in a 20W-50 in winter, probably not).
* FM/AW additive levels will be reduced proportionally. Something that is 1000PPM becomes 900ppm with a 10% MMO brew. (Enough to be an issue in a 20W-50 which already has way more additive than any 30 can legally, probably not).
* Other additives, TBN similar to the above already noted, less additive over more oilvolume.
* Chlorinated hydrocarbons have their own advantages in boundary lubrication, and disadvantage other respects.
This case, a 20W-50 in winter, if it feels good do it...I'd have serious thought of thinning/diluting some of the thinner oils.