GMC Sierra blowing luke warm heat - AC Auto Repair Help Forum


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GMC Sierra blowing luke warm heat

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Rangoonboth
New User

Jan 13, 2009, 7:49 PM

Post #1 of 3 (2159 views)

GMC Sierra blowing luke warm heat	Sign In

I have a 99 GMC Sierra 4wd, 110K miles, 5.3 ltr. The heat coming out of the vents is not very hot. (Blower motor works great).
Temp gage shows normal (180-190) I just replaced the thermostat and it made no difference. I have never flushed the radiator, The coolant looks clean.

My thoughts are 1: the heater core is clogged or 2: my flapper door thingy is not fully going all the way to the heat when I select it .

Any of these seem likely? or is there something else I am overlooking.

Thanks, Eric

Tom Greenleaf
Ultimate Carjunky / Moderator
Tom Greenleaf profile image

Jan 13, 2009, 8:51 PM

Post #2 of 3 (2156 views)

Re: GMC Sierra blowing luke warm heat	Sign In

OE thermostat called for 187F. Hope you selected that one and not lower temp.

My gut says the core OR the hose connector at the engine (smaller or the one closer to water pump) is restricted from some cloggage more than the temp/blend door not moving all the way.

It's hard to put #s to it but return heater hose should be a tad cooler than input but not cold. Colder return would suggest that all available heat was taken but in short supply.

I'd still flush the whole system and forgo the DexCool that was probably orig anti-freeze for regular EG that state for any and all vehicles and absolutely don't exceed 50% antifreeze. When way too strong it doesn't carry much heat (BTU caloric value) to transfer,

T

Rangoonboth
New User

Jan 14, 2009, 2:44 AM

Post #3 of 3 (2153 views)

Re: GMC Sierra blowing luke warm heat	Sign In

Thanks Tom,
I ill go ahead and flush the system and see if it gets better.

Thanks

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