When i turn on the heat the cooling fan kicks on and the temp drops way down.

Fan wil be controlled by a temperature sensor, if you have been driving engibe will gethot and start the fan running, as soon as you stop driving the heat does not drop so quickly so fan remains running until the temp sensor detects that the temp has dropped below the threshold. If the fan just runs even after engine itself has cooled down may be a problem with temp sensor. suggest to leave car for about 10 to 20 mins after engine is shutoff and then go back and check if fan still running

You could still have air in the system but I would also check the water pump on this.

Using your tatco code reader, select current data (real-time data) and select engine coolant temp sensor (ECT). Run engine to operating temperature (A/C off). Monitor the temp reading - when the temp reaches approx 204 deg farenheit, the fans should kick on, after the temp drops to approx 198 deg farenheit, the fans should turn off. The fans are controled by the ECM (Engine Control Module). The ECM controls the cooling fan relays.

First check fuse if thats good then check the thermal fan switch. If the fan switch is corroded its not letting The pcm know the temp.

Your overflow cap could be your problem. The cap may no longer hold pressure like it should causing small leaks that you don't notice which will make the car run hot. Also it could be the fans not kicking on because of a bad temperature sending sensor. If these go bad, the temp switch don't know how hot the coolant is therefore it will not signal for the fans to turn on to start cooling.

it will come on but only when the engine is very hot and the first fan cant cool it down that fast,, its turned on by a difrent heat censor so the engine needs to be realy hot to set the second fan running and it may even then only run for 30 seconds till the engine temp drops off,,, as long as the car is running in the normal heat range dont worry about it,,, if its cooking way up in the red,,,,,now worry about it,,fast too,,

try the fuse,if not that the wiring is bad from the fan to the switch.

temp gauge working proprely?turn on ac both fans should kick on after a few if not replace it

hello, have you ran a scan tool on it yet to see if its not your coolant temp sensor or other temp sensor if you don't own one you can have any place like auto zone run one for you for free you'll have more of a idea of whats wrong even if your cooling fan is at fault it'll let you know. when your chevy is at idol if the cooling fan is'nt kicking on then that's a good starting point,also check to make sure your anti freeze is'nt low and easy but over looked problem and your anti freeze cap could be bad and wont force the right amount to pressure through the cooling system also make sure you dont have air in your system when you changed the thermostat did you bleed the system through the bleeder valve mounted on the coolint system.and make sure your drive belt has proper tension even though you replaced the pump the drive belt has to be in good condition it drives the pump.also check your cooling fan fuse and the relay for it.

if ac dont work idleling it start to work when you move our fan is not coming on because when you activate the ac compressor kick in and fan should come on if it start to be cold only when you drive the force air cool the condensor ac work temp goes down HOPE IT HELP FIXYA OUR POST THANKS . PIERRE