WHEN IT RUNS WITH THE HEATER ON BLOWS GOOD HOT ...
2002 GMC Jimmy
March, 6, 2013 AT 6:35 PM
When it runs with the heater on blows good hot air. If you turn fan off it will over heat and has a gauge on dash. Replaced thermostat also didn't help. Can't see any leaks and fan spins while engine off and when it is cold fan is running as soon as you start the vehicle. Any ideas?
Check the cooling fins on the radiator to see if they're corroded and crumbling away. It is not giving up the heat to the surrounding air. The heater core is doing that job when you turn the heater fan on. The clue is the radiator hoses will be hot, not cool.