Differential gets very hot when towing, should I be concerned?

[jimmyess333]

Thanks for all the info.
BTW- that cover is a work of art and I like the drain plug.

The rear has new fluid in it but it's just the standard Castrol stuff off the shelf.
I changed it last year when I put the chrome cover on, then again recently when I put a new pinion seal and axle seals in.

 

[Will]

The 14-bolt in my pickup showed 165*F with a infared thermometer pointed at it after an hour at 70mph on the interstate with no load.

An old mechanically injected diesel like mine uses about .06 gallons per horsepower per hour and gets around 20mpg so a little math shows the engine is producing 60hp to maintain 70mph. I imagine a race car is using much more power, and with much less of an axle. I can imagine the oil would boil without a way to cool it.