Rear axle temps
Well, in cool weather, and no load I haven't seen the rear axle get above 150. When I hook the TT up and load my gear in cool weather I usually see about 175. Now, when the outside temps get to 95 and 100+ I have seen the axle temp get to 205-210 while towing (pulling a grade like from Sacramento to Tahoe area). In hot weather with no load, it will run around 160. This is all based on highway speed and long runs. Load and speed dictate the temperature. I have never weighed my rig but I am quite sure that I am close to my 20K GCVWR.
These temps were with Lubrication Engineers LE 607 in the axles. I have just changed that out and refilled with Chevron Delo ESI 85-140 in the rear and Delo ESI 80-90 in the front. As soon as I get the Drivers side mirror glass replaced I will be on the road with the TT again and will find out if the Delo makes much difference. The Delo uses a different technology and claims to run cooler, leave a thicker film on gear faces, and even increase fuel efficiency. We will see. I also have a LSD differential and with the Delo there was no need to use the additive. I have not yet driven it enough to determine if the LSD works any better.