We have a two speed gear box on a piece of farm equipment that runs the drive wheels. It holds about 5 gallons of oil that the manual says to use 80w-90 gear oil. The other day it got kinda hot and was puking oil out of the breather. The next morning I drained it and refilled with a 75w-90 synthetic. After operating the machine all day the next day I checked the temperature on the outside of the gear box and it was about 270 deg F. How much temperature will synthetic oil like that usually hold up to?
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