Rear diff pinion

Took a thermal image of my rear diff, now I'm worried. Normal or not?

Hi Frank,
Well Frank really... you are the only one I know that has all these gadgets and to even think to take a thermal image of his diff but seriously when I saw that yesterday I did consider if it was normal and what could have caused it if not.
So here is some guesses, the ring and pinion have a lot of pressure against each other and could cause heat but is what you have normal...I dont know.
Has it been set up and shimmed properly because if not there could be too much pressure on the cogs causing heat.
Since seeing how precise Vince's diff was set I realised that there is a lot of shonky operators out there.
All I can suggest is that I know Vince's is done right and if we take his for a run then take an image to compare with yours.
What thoughts do others have.
Martyn

Do you know the actual temperature gradients for the picture, ie what colour reflects what temps and at what temperature point the colours change?
Also a good idea to indicate how long after stopping the picture was taken, ambient temperature, driving speeds, distance and conditions like climbing hills, cruising at 100kph uphill or downhill etc before the temp was taken. As all these will affect results.

A few years back I did a "scientific" comparison of component temperatures:

After upgrading my rear diff to an LSD and a longish run, I did some testing:

Engine sump was very hot.
Clutch housing was cool.
Gearbox was also quite hot.
Transfer Case (NP205) was cold (presumably 2WD straight through, no gears in use).
Rear diff housing was quite hot (but the tubes were cool).
Hubs were all faintly warm.

Diffs do run very hot which appears to be normal.

My mate Dave in Perth said once, "if you spit on a diff and it sizzles, that's OK, if it spits back it's too hot".

90-100ºC is not abnormal for truck diffs (Google Diff Temperature), which is why Oka rear hubs run warmer than the front, there's heat conduction via the oil and axle shafts.

Engines routinely run at or around those temperatures and survive.

Along slightly different lines but not totally unrelated, over forty years ago when young and silly and when 4wd's in private use were rare a groups of us with early 40 series Toyota's did a bit of an experiment with dumping hot drive trains in cold water. Driving a vehicle into a cold river crossing with a hot drivetrain rarely caused problems with water ingress but if the vehicle stopped in the water then water ingress was assured even with extended breathers. A cold vehicle subjected to the same treatment rarely had water ingress and even then it was minimal. Most water ingress was usually restricted to diffs and wheelbearings with only an occasional gearbox getting water in it when the gearbox was usually immersed over the top of the gearbox or up to dash level in the vehicle. Immersion to dash level would also usually result in water in the fuel tank if left submerged for long enough.
As all 40's in those days were petrol powered we usually just dragged them out, loosened drain plugs until clean oil of fuel ran out of each "container" and continued on our merry way.
Quite a few times the high mount Warn winch operated flawlessly underwater, as well as the battery of course! Our weekday evenings were spent repacking wheel bearings and prepping the 40 series for the next weekend adventure.