you properly know this but just my 2 cents...
there are 2 sensors on the thermostat housing. Since they are independent I just check the readings on both and if they are the same than I believe both sensor is working properly.
one sensor reports the temp to your odo..
the other sensor send readings to your A/C system which you can read the temp in diagnostic mode.
I think considering they are independent, comparing the 2 readings very much gave me confidence that my sensors are in good conditions. Unless these sensors have a history of failing at the same rate and at the same time. Highly unlikely I would guess.
aux fan?? I think they come on at 100 degree and off at 95 degree without modification. They also come on at XX bars when the A/C is on.