Which differential oil is better?

[Iahawkeye]

I have spent a lot of time reading different things on which differential oil is the best. I dont want to open a new can of worms, but...

Will the mobile 1 75-90W oil work in the front and rear differentials? Am i better off spending nearly 3 times the money for the GM oil at the dealer? Should I wait unitl i can order the amsoil?

We are having decent weather in Utah (50 F) and would like to change the oil in the differentials and transfer case this saturday. I already have the trakII oil from dealer.

Lastly, the envoy has 86,000 miles.

Thanks for the advice and help!!

[markarock]

As long as you don't have a G80 locking rear differential, you will be fine with Mobil 1, Valvoline synthetic, Royal Purple synthetic, Catrol synthetic, and a host of others, including Lucas and Amsoil.

My personal opinion is that it doesn't make a difference for these gears.

My other opinion is that it is not worth spending the big bucks for the GM fluid, unless you are just topping off the front diff, which is what I did. I would not mix and match. It might be ok, but I wouldn't take the chance.

Just my opinions.

[the roadie]

I have the G80 and used Mobil 1 at 50K miles for the replacement. No issues. A true LSD like in the SS needs a clutch additive, but only a minority of G80 locker folks have reported noises that went away after adding it. The factory manual doesn't recommend it, but there might be a TSB that says to try if you have noises without an additive.