Corvette Forums - Corvette Enthusiast Site

I have a 1991 c4 The car hasn't over heated on me yet ( I won't let it ). I have changed the thomustat checked the collant and changed the coolant. The car still want to climb up 3/4 of the way to 260. What I have noticed is that when I turn on the auto switch on temp control the fan will run but if the I have it turned onto anything else it won't run. The second fam has yet to turn on. (thinking) that fan will not come one intil to late. What I have also notices is that same auto switch, if I push it and then go to something else like the defrost the fan will still stay on.
What is causing this to happen. is it the wiring or what? Or is it made that way (I don't think that just a stupid thought).
Thanks
Turley849