Now that the battery situation is clarified (and thanks for the moral support to all who responded) I need to change the front differential oil. The car has the 4EAT and I flushed the trans. about 6 months ago.

 

The owner's manual specifies a variety of gear oil weights for this app. I will probably go with the 80W-90 given the climate ranges here in the NE. What brands of gear oil are preferred by the community? Synthetic or no?

I've run Quaker State 75w-90 synthetic in my 86 and Amsoil 75w-90 synthetic in my mom's 97, both with trememdous success so far.

Well, the really big debate centers around what oil to use in the manual transmissions. You'd be hard pressed to tell the difference between two oils going into your differentials.

 

Synthetics have a number of advantages over mineral, but do cost more. I am a synth man.

 

Having experimented with most of the "big players" oils, I hold Castrol products in very high esteem.

 

Long story short, eh?

Red Line

 

its worth the extra dollars

Differentials are the one place where synthetics are arguably superior to conventional lubricants IMHO. The improved viscosity index may save enough fuel to offset the increased cost over the life of the lubricant, not to mention the better durability of the synthetic. I would use a 75w-90 rather than a 80w-90.

 

I have been using Mobil 1 75w-90 but will probably switch to Amsoil at some point.

 

FWIW we are currently seeing higher than EPA highway MPG in the outback during mixed (80/20) driving, and I attribute that in part to use of synthetic lubricants. Synthetic lubricants have a higher viscosity index, meaning they thicken less when they are not at normal operating temperature. This is where the fuel savings from using a synthetic comes from IMO, not because they are "slipperyer".