Question about 1999 GMC Sierra

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My 1999 gmc sierra heater doesn't work? it is blowing cool air not heat. the temp gauge is staying at around 200 degrees. so it shouldn't be the thermostat?? any help would be great!!

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6 Suggested Answers

6ya6ya
  • 2 Answers

SOURCE: I have freestanding Series 8 dishwasher. Lately during the filling cycle water hammer is occurring. How can this be resolved

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Posted on Jan 02, 2017

  • 1 Answer

SOURCE: NO HEAT

take heater hoses off and flush heater core these vehicles are known for this problem might have to do this every year

Posted on Nov 01, 2008

  • 1 Answer

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

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

  • 10 Answers

SOURCE: 1994 gmc safari,no heat

sounds like a blend door problem gm uses plastic clips to hold actuator rods that tend to break easiest thing to do is take it to a shop that offers free heater checks. and let them check it out

Posted on Jan 16, 2009

5 car stud
  • 10 Answers

SOURCE: 1999 Dodge Durango NO HEAT

Bad NEW thermostat? I had the same problem on my first generation Dakota. The problem for me turned out to be the DODGE thermostat I used to replace the old Dodge part. I went and got a Stant from local auto parts store using the standard temperature spec and quit shivering the next time I drove it. I hope that helps!

Posted on Jan 17, 2009

  • 90 Answers

SOURCE: 2005 GMC Sierra Overheating

If your sure there is no trapped air in system after refill and air bleed off, is fan clutch pulling good air thru radiator? Even if it is, the heater should have coolant as hot as what temp gage is showing! Try backwards flushing heater core (dex cool is notorious for plugging these up). There is a TSB for cracked cylinder heads from GM for unexplained coolant loss.Remove drivers side valve cover, and look at center three head bolts for coolant around them, if coolant has been getting in thru this suspect area, there will be a milky/pudding like goo under valve cover and on head. GM had a company called Castec cast these and the areas near the head bolts were found to be too porous (NO recall YET!) Ya, you guessed it, replace heads! Unfortunately, if its gotten hot to many times, it has probably hurt the heads/gaskets. Hope this helps. PS: The castec logo is under the rearmost pair of rocker arms,may have to remove them to see.

Posted on Feb 05, 2009

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