8 3/4 Rear diff. fluid

[JTG]

I have an 8 3/4 diff in the back of my car, its open for the moment, till I can afford the sure grip. I'm running 3.91's and the mechanic is suggesting to go with a thicker fluid (80w-90) since I'm not using a stock gear that the diff will have a higher operating temp. Good idea or bad idea.

 

[70DartMike]

I use 80w-90 in the Dart and its an open 3.23. Haven't had any problems.

 

[JTG]

Thanks Mike

 

[pettybludart]

I run the 80-90 in my rears,but just add the additive for sure-grips.I,ll run the same oil for my spool with 4.30,s.