axles getting hot

98 XJ, running 4.56's and 33's. I use Warren straight 90w gear oil in the axles, and after an hour of hwy speed (60+) diff housings front and back are so hot you can't touch them. After a couple of months the oil completely breaks down to a viscosity barely thicker than water. Is this normal, is there a different oil or additive I should be using?

Thanks

Did you Angle up the rear(And/or Front) axles to compensate for a lift for a more natural driveline angle? If so the Pinion Bearing and other parts of the upper housing may have oil starvation...

Something definitely isn't right there, willboy. That's not normal.

Even Dad's 35,000 lb. Dodge and gooseneck rig doesn't get that hot.

How recent are your gears? Have the gears blued?

They have about 7-8k miles on them, half hwy. The rear is tilted up about 4 degrees and the front has 2.5 degrees extra positive caster for drive line angles. I don't know what you mean when you ask have the gears blued yet.

I'd open up the diff and see if the edges of the gear teeth have started to turn blue from the heat.

Caveat: I am NOT a gear setup expert. But something has a little too much friction in there, I think.

(1) Extra positive caster would tilt the front pinion down -- are you sure you have extra positive caster? (Not that this should affect your diff temps.)

(2) You write about using Warren gear lube as if that's important. I've never heard of the brand. Is there something special about it? The FSM originally called for 80W90 GL-5 gear lube, and 75W140 synthetic for trailer towing. When they were having axle problems on the first WJs, they started using synth 75W140 in all the axles, but I don't know if that was all vehicles or only all WJs. If your lube is breaking down that quickly, I would suspect that it doesn't meet the quality standards required. Being a single viscosity, it may not have the extreme pressure additives required for a differential.

Try running with a good brand of 75W140 and see if that makes a difference.

It sounds like you are in part-time 4wd, and you are getting a binding between the front and rear. This would explain why the front diff. is heating up.