FILE

iTrader: (5)

A G80 will going in my friend's truck. Anybody know?

GMCtrk

iTrader: (27)

non syn

LS1csherm

03's and newer are factory filled with synthetic.

2ksleeper

per the my service manual:

SAE 75W-90 Synthetic Axle
Lubricant (GM Part No. 12378261)
or equivalent meeting GM
Specification 9986115.

P.S. My truck came factory with a G80 before I yanked it out & I believe the diff housing had a tag on it that stated to use synthetic oil only.

GREGGO

iTrader: (2)

I'n my Auburn, I use Mobil1 Synthetic. I also use the GM additive for posi's.

Mort

Use the GM Synthetic and no additive with the G80.

goshawk23

i use synthetic with the gm additive.

chevymec

iTrader: (19)

I dont think the additive is recomended with synthitic fluid. .With posi units like the Eaton in my camaro, it said to use regular gear oil with the additive, not synthetic.

James B.

iTrader: (1)

GM synthetic differential lube has a bad habit of evaporating if it gets too warm. I keep in touch with a GM driveline tech who showed me serveral rears that completely cooked themselves after the factory GM synthetic fluid vented. It's okay to use synthetic lube in a G80 but personally I would look toward an aftermarket product. The GM stuff is also absurdly expensive.

Mort

When I checked with Amsoil they claimed they did not have a product compatible with the GM 75W-90 Synthetic gear oil and that the GM fluid should be used? Someone else checked with Mobil 1 and got the same result. So while the aftermarket products may work they are not supported by their makers so I decided to use the GM fluid.
No additive is recommended with the synthetic fluids.