Just for the heck of it, i picked up the gallon of 85w140 gear oil that was out in the shed yesterday. It was about 20F here yesterday. Man that stuff is thick. It would barely pour out of the bottle. I would definitely not want this stuff in any diff in the colder weather. I would bet at 0F it is most likely solid. On the flip side, the M1 75w90 was still nice and fluid based on the shake test. I wonder how the 75w140 synthetic would be?