Diff. Temps? How hot do they run?

[Steve O.]

Finally installed a rear diff temp gauge. It is in the top of the pre-tapped Mag Hytec diff 14 bolt cover I put on.

I am seeing what I have to imagine are crazy temps. Today, a really hot day around here, (90's) they got up to an indicated 250 degrees, almost maxing out the gauge. I was not towing, and the truck was empty. Diff is full of gear lube, up to the extra capacity the bigger cover allows.

On a recent cooler day on the highway they were hovering around 210.

The number are either:

1) Wrong and something is messed up with the sender or gauge.
2) Correct and there is something very wrong with my rear gear set. (Although it looked great when I had the cover off and there is no noise coming from the back, that I can hear.)
3) Normal and I am about to learn that from someone here.

I have no frame of reference on what the temps should be, so any input would be appreciated.

As always, thanks.

Steve

[tanker]

Well Steve, you didn't worry prior to installing the gauge, did you? :rolleyes: I went through the same thing when I installed mine in my ole suburban. I don't remember what temps I had, but I think towing once in +90 degrees it went up to 280+ degrees. Mine was relative to ambient temps, speed and load. I would check the diff temp with a hand held thermometer, just to see how close you are. Does it ever go to ambient temps when sitting overnight?
You could have a difference in calibration between sender and gauge.
If it checks out OK, You may have a bearing getting hot, but check it out first.
What did the magnet have on it when you removed the original cover? How id the fluid look?
If you have driven for a while, pull the dipstick and see if anything is on that magnet. I used Amsoil snythetic gear lube, and changed it each year when towing. ;)

[TJ Moose]

Yeah - sometimes seems like a little extra knowledge is a dangerous thing. Maybe an easy way to double check is to get one of those laser temp guns that do a point and shoot temp readout. Then you can spot check temps, at least from the outside of the housing. Could tell ya if a particular bearing is getting hot, or if its an overall thing. Since a diff is like a big heat sink - even sender placement could make a big difference. Makes a case to go to passive cooling - like a finned diff cover. But truest statement is - "Was it ever a problem before?" Maybe if it ain't broke don't fix it? That plus use synthetic oil in the diff - which will help squeeze a little more temperature range out of the lube if indeed you really do have a problem.