Hope somebody can help with this question so that I don't go replacing things that don't need replacing. The main cooling fan comes on after start up at about 150 -160 degrees and works so good that it doesn't allow the engine to get to operating temp. (180 thermostat) Its cool here in northern Illinois now. After some driving it does go off, and everything is normal after that. Its an 89 with the aux. fan option, and very few mods: flowmasters, TB bypass, frisbee off, and manual fan switch so that I never let the temp go over 200.
Any suggestions are appreciated! Thanks.

 

Are you sure your dash sending unit is accurate? Compare it with your oil temp. It should be within 15deg under normal conditions.

Do you have an aftermarket chip, like Hypertech? That'll do it.

It's also possible that the coolant temp sensor for the computer on the front of the intake manifold is not reading correctly. The computer could be receiving a 228deg signal from it when it's cold. This is a seperate sensor from the dash sending unit.

 

Think about how the cooling system works and then reread what you have written. The fan blows air across the fins of the radiator to help remove heat. The heat is produced by the running engine and the hot coolant is circulated by the water pump. The thermostat stops the water from circulating through the radiator, until it reaches a predetermined temperature, in order to speed warm up. It would be impossible for the fan (or radiator) to keep the engine below the thermostat temperature, as the thermostat doesn't allow the coolant into the radiator, until it opens. Among other things, I think you have a thermostat that is stuck open. Certainly there are other possibilities, like a bad coolant sensor, etc., but I think the stat is the most common and likely cause of what you describe, and all it costs is a 25¢ gasket to test it.

The next problem is the early fan activation. Chances are, it isn't so much a malfunction as it is the subject of a previous owners modification. The main fan is controlled by the ECM. The auxiliary fan is controlled by a thermal switch in the left head. There are several ways to make the fan come on earlier. If the two fans come on at the same time, chances are there was a cooler thermal switch installed and the two fans were tied together. The most common method is to reprogram the prom, which only affects the main fan. The puzzler is that "After some driving it does go off, and everything is normal after that.". That, and the manual fan switch suggest a short in the wiring somewhere.

RACE ON!!!

 

http://members.shaw.ca/corvette86/Co...%20Control.pdf

 

Thanks, I think I'll try a new coolant temp sensor. Appreciate the responses.