Rear end temp

Eaton conducted tests on oil/component durability during the late 1980s early 1990s

Their intent was to maximize seal and gear life and to allow the maximum OCI possible for their Heavy Truck gearboxes and diffs when using 75w-90 and SAE50 gear oils

They found;
a) components should not be operated at consistent temperatures above 250F
b) Intermittent operations to 300F do not harm the components or oils (synthetics)

Synthetic gear oils (75w-90 and SAE50) reduce operating temps by from 10-20C