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Chevy/GMC Trucks \  Heater won't work

Heater won't work

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Hey whats up. I have a 2001 S-10 with the 4.3L vortec. I replaced my thermostat today and for some reason my heater is still blowing cold air. I just can't think of what would cause this besides the knob being broken or some shit. Anyone had this problem before? It's odd because I would understand the cooling system going out but not the heating. Hit me back up. Thanks guys!

check the mode door the one that switches hot and cold the motor could be bad that moves the door
Would that be right behind the dash right? The actual door right? I am pretty sure I understand what your saying but I don't think that is the problem. What else could it be if it wasn't that? I've never had this problem before until it gets fucking cold outside.

-Jared Oeltjen
sounds like the thermostat could be stuck open. Start the engine while its cold and check the upper radiator hose. you should have no coolantgoing through the hose until the motor gets warm and at that point, the hose will feel warm. If the thermostat is stuck on open, you will be able to feel the coolant in the hose as soon as you start the motor when its cold
Cool, I will check that out. Thanks guys for helping me out on that!

-Jared Oeltjen
make sure the ball on the hood has a vacume line hooked up to it also. that controles the doors also on the hvac system on s series trucks
I would also check the hose coming off the top of the intake going into the heater core. The hole in the fitting coming off the intake could be full of crap. The dexcool in the 4.3L's turns brown and starts to gum up everything inside the motor. I would say flush the whole coolent system. You can buy a acid cleaner to get all the dexcool out of the motor and change it to the green kind. Or if you have ever mixed the two coolents that will cause some problems too.
Yeah I heard about mixing coolants. I think I am going to flush it today. I will get back to you guys. Thanks for the input!

-Jared Oeltjen
I had the same thing happen to my 89 gmc fullsize, i don't know how much different they are but when that happend it was because my heater core went out. You might check that too.
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