What is the FACTORY differential fluid?

[WOT]

It is about time to change the rear differential and was trying to find what weight oil was in it from the factory. Can't seem to locate any posts that mention what the FACTORY fluid is.



I picked up some Amsoil 75W-90 (standard) from the local store, but now I am wondering if I should use the 140 stuff. I tow in the summer usually about 5,000 miles or so (usually in 5-10 hours spurts).



I will put 75W-90 in the front for sure, but I have seen mixed opinions on the rear. Knowing what the factory stuffed in there will help me make up my mind. I have 44K on what's in there now.



Thanks!

 

[John Berger]

The factory stuff is SAE 90. If you tow that much, you should consider the 75W-140. You will have to be careful in the winter up that way, but if you take your time and go easy until the truck warms up, you shouldn't have a problem.

 

[tlippy]

When you remove the cover, you're gonna really be suprised! The OE oil will be foamy muck. I changed at 40K and used Red Line synthetic 140. I too was concerned about the viscosity, but some of the TDR members have installed a temp. gauge and most report that the rear end oil runs close to 190 degrees unloaded. So, I'm going to stick with 140 wgt