If they tested straight 90 weight gear oil at 0 deg, it would probably come out at about 140W-90 (yes, you read that right
).
So 20W-20 would be the same viscosity at both 0F and 130F.
I ran 140 weight in my Model A (Straight Tooth non-synchronized) tranny. Then I got clever and put some STP oil treatment in it. One morning it was in the 30's and I nearly bent the shift lever trying to get it into gear.
