Hi, posted this on TDR as well but things seem a little slow over there...<br><br>My rear diff is running hot enough that my buddy noticed steam coming off when I hit patches of water on the highway, too hot to rest your hand on the pumpkin. This is running unloaded @ 65mph, truck has 18,000mi now with Dana 80 3.54 LSD.<br><br>Any thoughts? The fluid is 1/2&quot; - 3/4&quot; below the plug, quite black and dirty but doesn't smell burnt.<br><br>Rich

 

That's probably normal with a petroleum base gear lube in there. The fluid capacity sounds right.<br><br>A read a post somewhere by a guy into racing. He said they'd change the rear gear sets on the car during time trials to get the best results. If they'd use petroleum lube, they'd have to wear gloves or receive second degree burns to their hands, when changing sets. Running Mobil 1 synthetic gear lube, they could change the gears with their bare hands after a run.<br><br>I'd recommend changing the fluid to a good quality synthetic, either a 75W-90 or xxW-140. Mag-Hytec makes a replacement differential cover with cooling fins that adds a few quarts capacity as well. I think synthetic fluid is a benefit here, compared to in the crankcase.

 

Time to change oil sounds like wrong fliud in diff. Its black because its over heating try useing synthetic

 

I dumped my diff at about 2000 miles... it was black and nasty. Change it out to a nice synthetic of your favorite brand (I use Royal Purple 85W-140 in mine) and you will be better off. Besides, if you tow at all, the book says to put in synthetic! ;D<br><br>Tony

 

I would say if steam comes off it, when you are not pulling anything, would be too hot! Something doesnt sound right to me. I have felt a real warm diff. but not hot enough that I couldnt touch it. Pulling can be another story.

 

I agree with everyone else, change to synthetic.<br>I use Amsoil in my rears, tranfers case, auto tranny, and engine, but you must decide what you would like to use.<br><br>Chris

 

I recently read somewhere, (can't find it now) that it is best<br>to overfill a Dana 80, back it up on some ramps or somehow get the back of the truck up as high as you can get it and fill until it is coming out the fill hole, anyone ever hear of this?

 

When I was considering the Mag-Hytec rear cover, I once felt my differential housing with the stock cover after driving 250 miles at speeds of 60-75 miles. It was warm, but no where near the temperature you describe. My bet is it's not shimmed properly and you're experiencing a really bad lash. Cool oil is essential to work harden the surface of the gears. If temperatures are too high, the gear surfaces will not work harden, and in fact you risk softening the gears instead. You need to have someone that's good with rears to check that ASAP.

[edit] Another thing you might want to look at are the bearings. One or more of them could be bad. I think I remember reading one another diesel site about the Dana 80 and roasting bearings. Can't remember where though.

 

Thanks for the feedback, I'm going to have to get somebody to check it out because I think it's more than just oil related. Maybe it's been tight all along and that's why my fuel mileage is poor. I might take it to a rearend shop for a quick check before risking bomb-induced voided warranty at a local DC dealer who may or may not be good with rearends.