Sorry, the wording is a little confusing. Are you saying that it maybe too cold in MI, and the 85 will not suffice?? Even though, I am here in MI and see it on the shelves everywhere? Cuz the actual question was "is the exact weight crucial" and you start off by saying "I'd say not" which sounds like you suggest it is fine, then proceed to say that it may get too cold in MI for the 85w..which then suggests its not a good idea. Sorry for the confusing, may be due to lack of coffee this AM.

 

I think that he is trying to say that the 85W would be too thick in the winter months, especially since you are in MI. Typically you can find a lot of 85W-140, but most of those are dino (conventional) oil. All of the 75W-140 that I have seen is Synthetic, which is what you need to run in the diff. My Oreilly's had Valvoline and RP in stock and could order Lucas and Mobile 1 in the weights that are needed (75W-90 up front and 75W-140 in the rear)

nateroach