Gear Oil Question

[jasongt06]

Why did Ford change from using 75w90 gear oil in the 8.8 to now using 75w140 in it? Wouldn't 75w90 return better economy and performance?

 

[Fourth Horseman]

Just a guess here, but better wear protection over a wider range of operating temperatures? I've been running 75w140 in both of my cars (my Marauder had 75w90 from the factory, not sure about my Stang) and haven't noticed any obvious difference in gas mileage, though I'm sure in theory there must be some.

 

[NastyStang113]

The difference in gas mileage.