I just purchased an 03 3500 after 10 years in a PSD, very impressed with the Dodge!!! In checking the service manual I see differential oil change is due at 30K. I work for a trucking company and we run syn 75-90 in our Eaton rear ends and change it every 250K... I imagine some folks here have some experience with synthetic oil in our trucks? Bob P.

 

Welcome to DTR. Factory fill is synthetic 75w90. It is suggested to change the fluid the first time a 15,000 miles but I changed mine at 30,000 and it was O.K. I use Amsoil 75w90 severe gear lube. Many on here us Mobil ONE Syn. 75w90.

 

I used Royal Purple.

 

I use AMSOIL 75/90 or the new 75/110

 

Welcome to the forum, NYTCTD.

The service manual specifies 75-w90 full synthetic that meets GL-5.

Lots of people who tow heavy in hot climates run 75-140, which I run on my dealer's advice. I've been using Redline with good results, and will follow the 15k thing, at least until the warranty expires.

Gasket is reuseable. Book says 30 ft.lbs cover bolts and 24 for the plug, but there have been a number of threads about cover bolts breaking before reaching 30 ft/lbs so you might consider going a little lighter.

Jeff

 

I've been using the Schaffer's 80w90-- have 115k total miles. Last change was at 100k and the gears looked like new and very little wear metal on the magnet. I changed the original fluid at 15k, 2nd change at 50k, last change at 100k. Tow about 8k from time to time and regular 2k loads in bed.

 

I know these truck have a AAM axle which is the same used behind the Duramax and Chevy recommends 50K or 100K change intervals with syn oil. So i think your OK going a little longer, expecially with a good oil.

 

Amsoil 75W90 during warranty, then I'll probably goto amsoil 75/110 or 75/140.

Oh, and the Mag-Hytec diff cover is worth it's weight in gold for ease of maintenance. There are also PML covers out there, but I have no personal experience with them.

HTH

Tony