05 Ford Explorer gear oil question

[threeputtpar]

Had the same issues with the rear diff whine on an 05 Mountaineer. It was there when we bought the thing with 9k miles on and it was still there, no better or worse, when we traded it at 110k miles. I tried a couple of different fluids and nothing changed. It would only whine from 50-62 mph, and only while accelerating or holding speed. When I would let off the gas and coast the whine would go away.

A friend that works at a Ford dealer said they now spec 75W-140 for all rear ends because of the problems they had with the previous gen Explorers/Mountaineers/Aviators chewing up gears with 75W-90.

If you can live with the whine, it doesn't affect the longevity of the ring and pinion one bit. I changed the fluid twice over those 100k miles and after the initial fill was dumped it always looked like new fluid coming out.

 

[lugNutz]

Yeah, pretty sure it's not the bearings. I have no play in the wheels and no noise unless I am on the gas. Differential is definitely which direction I am leaning. If the sound were more of a howl, I would think bearings, but this is like a whine, which the volume varies with speed.

This is the sort of sound I get, not 100% accurate, but you can get an idea.

 

[RedOakRanch]

Threeputtpar described the exact symptoms that were my wheel bearings going out. I drove it that way for years (50k miles) thinking it was the gears. But the gears are a common problem so I won't push the bearing possibility any more.