Dumb question (about tranny fluid)

[Rawze]

I have always run 75/90 (or 80/90) synthetic on my Eaton 10-speed tranny. Here were the results...

http://rawze.com/forums/showthread.php?t...6#pid52116

Different manufacturers have different requirements though. The manual/book for my tranny says to use 50-wt oils, but I knew the gearing, etc. was just too large for this light weight of an oil, so I went with my gut instead. Only reason i use synthetic instead of dyno oils is that we do go to the northwest in the cold in winter months. The tranny does not have a coolant-fed heat exchanger on it to keep it warm (I hate those things),.. so the synthetic was chosen simply so that it did not get real thick in the extreme cold.

We also change the oil out every 250k miles or so.