Pontiac Repair: thermostat/overheating/fans, rear cylinder head, coolant temp

Question
I have a 94' Grand Prix se 3100 V6. Thermostat seemed to stick so I replaced it and found that the old one was fine. After installing the new one I found that the fans were not working either. I jumpered the female ends of the coolant temp sensor and fans came on so i replaced the sensor. Fans still don't work. Also if i let the car warm up before driving it the thermostat wont open (temp gauge goes up until the warning light comes on) until I drive for a while. But if I just start it, let it run for a couple minutes it acts fine minus the fan issue. Recently I did not let it warm up and the temp gauge warning light was on within a couple minutes in 32 degree weather. What could my problem be? Thanks for your help!

Answer
Hey Dan.

This car the engine control module runs the fan relays and the fans. You could have a temp sensor that's reading wrong and not turning the fans on at the right time. The gauge on that care uses a seperate temp sensor on the rear cylinder head. The one for the engine computer is in the lower intake manifold. You could have an engine mechanical issue with this when it's pretty cold out even with out the fans it shouldn't peg the temp as long as you have cold air flowing across the redaitor it should keep it relativly cool. You may have a head gasket going bad or some other type of coolant leak and the system has air in it and that will make it act erratic as well. You could have a engine computer that's bad and it's not turning the fans on at the correct temp You need a scan tool to see exactly what's going on with the engine data and fan data. Good luck and happy holidays :}