synthetic 75/90 or 75/145 rear diff fluid?

[tuner-automotive]

Im changing over to full syn oil and am doing the rear diff 1st.
Im looking at red line and they only carry it in 75/90 or 75/145.
I live in oregon and the weather stays between 35-95 deg.
Im also looking at Mobil 1.
1990 GMC Jimmy 4x4 5.7l 350 10bolt rear and front.

 

[rjfguitar]

I use Mobile 1 75/90 Syn. in all of my differentials

 

[tuner-automotive]

Yeah , after thinking about it Im gonna go with Mobil 1 thru out the entire rig.
I whish I could find a mobil 1 synthetic ATF for the trasnfer case?

 

[Pookster]

advanced auto, autozone, and even wally world have synthetic ATF.

 

[tuner-automotive]

Who makes the walmart brand oils?
I heard somewhere it was penzoil product?

 

[dunehopper502]

quaker state makes walmarts products under the name supertech...

 

[Supreme70]

can u break in a diff with synthetic????

 

[tuner-automotive]

so thats a yes then?
penzoil/quaker state is the same co. , right?

 

[rjfguitar]

so thats a yes then?
penzoil/quaker state is the same co. , right?

I don't think so on that one. Napa brand oil is Valvoline, outside of Mobile, I think Valvoline is the best.

 

[rjfguitar]

can u break in a diff with synthetic????

Yes. The main reasons why I run synthetic is because of two things...

1. Syn. handles heat better. I'm sure the D70 in my '01 Ram cummins will be working hard pulling my gooseneck and K5 this summer. THe added protection can't hurt.

2. Out of all the fluids on a vehicle I would say the rear end is over looked the most. Hardly anyone even knows what a rear end is, much less how to change the oil in it. Syn. oil lasts longer than conventional oil.

Reason number one would apply to breaking in new gears, lots of heat at that point.