I just had new Eaton e-lockers and 4.88 gears installed front and rear of my 2010 JK, D30 up front and D44 in the rear. The guy at the shop that did the install said to use 80w90 gear oil but the manual for the e-lockers say to use the factory recommendations which is 75w90. I guess my question is what is the difference and which should I go with? I just finished the break-in period and it's time to change the gear oil and go play!

 

Either would be fine.

 

Whichever you can find at your local autoparts store.

 

The difference is just the "Winter" (cold temp) viscosity, the 75w would be slightly less viscous when cold. The second number (90) is the the hot viscosity grade. The 75w might be slightly better in cold climates, both have the same (90) viscosity hot.