Can someone tell me what grade oil I should use in the rear end. Amsoil offers 75W-90 and 75W-110. Which should I use in my new 09 3500 dodge.

Dauntless

 

AAM recommends 75w-90.

Higher viscosity gear oil isn't always better.

 

where are you from? I've seen some say to run the 75-110 in cold climates while others use 75-90 no matter the condition, I personally run Royal Purple Max Gear 75-90 and love it though.

 

75w90 is what the specs call for.

 

I checked here and several other forums before I changed mine at 15K. Most of the hotshoters that use the trucks daily for towing are using 75W-110. I do not pull every day, but do pull a 5er for camping during the summer camping season. So I put in Amsoil 75W-90 with a Mag-Hytec Diff cover, used 8 Quarts.
Just my $0.02

 

OEM fluids are synthetic in the diffs already. Why the quick change?

 

Per Dodge requirements ( in your owners manual) the front and rear diff fluid must be changed at 15K. I tow a 5er during the camping season thus I follow the manufactures recommendations. I also installed a Mag-Hytec diff cover on the rear axle for more cooling and more fluid capacity.

 

Fair enough...