There are two gauges for the tandem axle oil temps. Do I have a defective gauge. The leading tandem shows the needle moving up some. The rear tandem gauge does not move.
Could it also be the fact that the rear tandem is not locked(engaged) and therefore not being driven by the driveshaft and not creating friction heat.

 

They do not have to read the same. Not uncommon for the front axle to read just a little warmer. I was once told that it's the proximity to the engine. The air around it us just a tad warmer than the rear one. If it does not go over 250 degrees, I would not worry about it. If it does, keep in mind that the source of heat for the lubricant is warmer than the lubricant itself. When metal parts go over 300 degrees, you begin to change the characteristics of the metal. That's where you can do varying degrees of damage.

 

The rear tandem is receiving torque all the time from the engine.

The front one always runs hotter, that's just the way it is. More moving parts.

 

The sending units are notorious for acting up on those gauges either that or the wire falls off. It's usually around 20 bucks for the sender and lather silicone over that wire to keep it from going green.

 

I agree, a quick check is to just look and see if the wire is connected... but, be aware that some silcones react with copper (corrode the wire).

Axle temps will be higher as loads increase... what is a good operating axle temp under full load???

How much heat change will you see on a hard pull up a long grade???

P.s. make sure you put pipe dope on the sensor before you thread it in... or it'll likely leak.

 

According th Eaton, 180 to 220 is OK temps for both of them.

 

I've never been told just what the temp differential is between the metal parts that produce the heat, and the oil. The theory would be the same as "the frying pan is never as hot as the fire under it". I would expect about a 50 degree difference. But I do know that if the bearings get to 300 degrees, they will not last long. It changes the "tempering characteristics". Soften the metal and you'll be replacing them in a short time. Same goes for the gears.

 

I wouldn't imagine it would be very hot. There is no "combustion" in your differential.

A lot of the heat would be created by the oil itself. Being squished around, that's what heats it up real good.

Front hubs, on the other hand, don't get anywhere near as hot. There isn't really "squish" or "meshing" going on. Hell, same with the diff hubs. They don't get hot, unless theres something wrong with your wheel bearings.

 

Or brake drag...

 

The oil is actually responsible for lowering the operating temperature. It lowers friction between gear sets (where most of the heat is created, except for the engine induced heat ;0), and it also dissipates heat, or carries it away from the hot gears.

No, the hubs don't usually get very hot... unless you lose the oil!!!