"rule of thumb" for gearing in general is 100F above ambient and usually the "limiting factor" is the max temp of the oil or the seals. ( some variances there )
The rule of thumb held true for the 1st 2 GBs 145-150, but the rear GB was 120-130 above
You said one at 60F and one at 90 ambient- what are the uniform temps at a given ambient? ( little confusing there)
The day I checked it was 60F, and GB was running 180-190, so about 120-130 above, so I guessed that at a 90F day , GB would be running 210-220
"heat" (in and of itself) is not always an indicator of a problem but differences in heat frequently is an indicator of a problem.
What you should look for is differences in like boxes and then heat "zones" ( If the heat uniform or focused in a particular area)
Then look for additional clues ( loading, alignment, tension [if a belt system], smell, noise etc.)
All 3 GBs are in the same heat zone & load, alignment should be OK as universal joints are not running hot and no drive line clatter
Those claims are often misstated and taken out of context or spoken without proper qualification. If changing the oil 3 times has not produced a noticeable difference- it aint the oil. Look elsewhere.
I am looking elsewhere, as I said if magnetic drain plug has lot of crap on it, I know what to do
