I recently had a leak in my radiator (and car was overheating) so i had it replaced. Upon driving it around for a while i noticed it was overheating again.
So I replaced the thermostat. Still overheating.

So then i noticed that when i had my a/c or heat on it wouldnt overheat... so i popped the hood turned the heat on and the fans started spinning immediatley. Turned the heat off.. fans stopped running... So now i just drive with the heat set to 1 all the time and the car runs fine.

anyone know what this problem could be?

 

just having the heat on alone it should not make the fans come on unless u also have the a/c button turned on..............

chk make sure u got planty of coolant, bleed the system, make sure thermostat opens properly, if all is ok ,,you mihgt have a fan switch gone bad,,,,,,it is the 1 with a green plug 2 wires located on the thermostat housing, ,,with a/c and heat off, and car warmed up, unplug the switch and jump the 2 wires together ,, try and post results........

 

It seems like there is a slew of possible temp switch failures as of recently. I agree with desert, it is probably the switch. Unplug it and jump it like he stated, and the fans should run. The switch is only like 50 bucks.... something like that, don't quote me on price.... and it would take about 2 minutes to install. Just for further thought, and to avoid problems, (comebacks).... whenever I replace coolant, a water pump, tstat, radiator.... I always bleed the coolant to remove the air, and run it until the fans come on... to make sure it won't overheat when the cust takes delivery. I have caught more than a few overheating vehicles this way. Thats the tip of the day.