Question about 2000 GMC Sierra

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2000 GMC Sierra 5.3 Litre, won't blow hot air

I have a 2000 GMC Sierra and it just started not blowing hot air. I think it might be the thermastat?? Could it be somethng else? Where is the thermastat located. AC works fine. Air blows fine just cold when set all the way to hot. I drive it 20 to 30 miles and still no hot air. The temp gauge reads just below the middle.. ANy help you can give?

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  • RSamp83 Dec 18, 2008

    At idle my heater blows hot air. But when you excelarate it starts to blow cold. I flused out the heater core with a hose and the water runs out with no ploblems. The gage on the dash shows the temp to be 210.

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I experienced the same head ache. First attempt was to replace the thrmostat and after taking it apart I realized that there was nothing wrong with it. I then removed the plastic cover/panel located under the dash board on the passenger's side. (only a few 4-5 smalls screws) Removal will enable you to see the on/off switch/gate moving/rotating as you turn the knob to hot or cold positions, on the control panel. If that switch/gate seems to work ok, then the trouble is within the heater core. Many mechanincs suggested that I replace the heater core. A very expensive proposition.
I checked the heater core supply/intake hose and found it hot to the touch, while the return hose was nearly cold. It was definitely a heater core blockage. I removed both ends (supply and return) hose connections/clamps. They are located near the fire wall in the engine compartment. A special tool is very helpful to remove those clamps easily and to replace them as well. It can be done the old fashion way but this tool was a life saver and reduced work time to just minutes. (Tool is $70.00 bucks at auto parts store,so I borrowed mine from a mechanic/friend)
I then hooked up a garden hose to the return end of the heater core and reversed the flow of coolant/water through the heater core. My truck is a Sierra 2000 and I refuse to see how a heater core could get clogged up with clear coolant alone. To my surprise a flat piece of rubber about the size of a quarter blew out of it and the flow of water became unobstructed. I reconected the ends of the hoses to the heater core, replaced the lost antifreeze & everything returned back to normal. No money spent for something most mechanics suggested I replace control valves/switches ($280.00) replace heater core ($500.00) etc etc. I am glad I was curageous enough to tackle this myself and save a few pennies. Good luck, and I hope this will work for you.

Posted on Dec 02, 2008

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I had the same problem, I took it to the dealer, they changed the thermostat that I had already changed and that did nothing but cost me more money... It ended up being air in the lines, they flushed the coolant and force filled it back in and got rid of all the air in the lines and I had heat again.

Posted on Nov 15, 2008

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2000 sierra 5.3L- Just changing the oil and a 2 1/2" long x 1/4" diameter tube came out with the oil. Where did it come from?

Posted on Jul 23, 2009

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