I have an 02 Mountaineer with 90,000 miles on it. I just started getting a oscelating (sp) hum sometimes while I am turning. I am thinking that I will start with changing the rear end fluid and see if that does is. But I dont know if it would also be some sort of bearing. Any thoughts or input would be appreciated.

Also what fluid does Mercury recommend for the rear end with 90k miles?

 

The fluid recommended for these is 75w-140 Synthetic with friction modifier additive (for the limited slip)..

Does your Mountaineer have the independed rear suspension?? If so you may want to google "Mountaineer Rear Differential".. Tons upon tons of problems with these on the Mountaineer and Explorer... 90,000 miles is probably pretty good on one of those...

I think the root of the problem is the aluminum housing distorts along with some mighty cheap gears....

Doing away with the recomended fluid and using good ole 80w90 with lucas additive and friction modifier seems to help these... The only reason they are using synthetic fluid now a days is to decrease the resistance from the lubricant itself.. Makes the economy, power, andc emission better.. Longevity is still questionable.. Seems to be alot of rather low milage differential failures now days...