Diff Oil???

[DBoudreaux]

Is it safe to use 85W-140 Lucas gear oil in the rear dff? I have a 2008 4500 and I'm not sure if I'm supposed to use synthetic oil??

 

[TulsaOkie]

Thats what I've been putting in Mine for the last 320k, seems to be doing just fine.

 

[HBarlow]

I don't know about the 4500/5500s. They use a larger, stronger rear end. The 3500 comes with synthethic differential lube from the factory and synthetic is specified.

 

[Bug Out]

i have used Amsoil 75-90 Severe gear Syn with no problems. The R/E temp is usually similar to the m/trans temps, never higher then 210 thus far.

I have to admit, I really didnt want to see the temps after pulling the Eisenhower tunnel hill in Colorado, 11. 2K elevation... . It may have been higher there. . . the temps are pulling a 16K+ toy hauler.