I've heard of Alt's operating at 300F with no problem, but I'd set the alarm about there.
My belief is although they have done it for awhile and no demonstrated harm, effects may be cumulative and I don't want to shorten life. How hot can grease get and not oxidize and eventually not lubricate? Depends on the grease I'm sure and that may not be the most temp sensitive thing, maybe it's the insulation
? Plus where are you measuring the temp will I am sure be very important as I bet some spots of an Alt run very hot and some spots much cooler?
Maybe an IR thermometer to find the hot spot?
When viewed straight on, the hot spot on my alt seems to be the port side of the alt, the Starboard side of the boat
, the side closest to the engine
, is that common?, I have no idea.
Just a data sample of one.
I do know that temp is THE limiting factor on my 125 amp, I can't get near that amount of power, due to heat build up. Most I seem to be able to pull continously is about 80, maybe 90.
Gut feeling is if I could speed it up a lot, I'd get much more power and cooling