Heat question

Discussion in 'Chevy Silverado Forum (GMC Sierra)' started by Jeff Dodson, Jan 24, 2014.

  1. Jeff Dodson

    Jeff Dodson Member 1 Year

    My 99 NBS Z71. With this cold snap, drove the truck about 30 miles to school and the windshield would not de-fog. I noticed the heat was not getting as hot as it should. The temp gauge runs as it should, around 190-200. The heat coming out of the vents is not adequate . Blows strong, just not hot enough... Is there a common problem with these or what's the fix
  2. summitwhite11

    summitwhite11 Active Member 2 Years 500 Posts

    generally a good flush of the rad and a new thermostat is the starting point, a 15 year old truck can have a lot of build up inside. You can get a flush kit, ( follow the directions), or you can have it flushed.
  3. Jeff Dodson

    Jeff Dodson Member 1 Year

    Thanks for the reply, but that's not the problem. It runs at normal operating temperatures. Besides, it was serviced with a new water pump, flush and thermostat before I bought it. It's the heat blowing from the vents INSIDE is not getting hot enough. I believe the problem could be in the mixer on the dash ... Just wondering if there is a common problem with them
  4. j cat

    j cat Epic Member 5+ Years 1000 Posts

    lets say yesterday you had good heat. heat that would make you feel uncomfortable. now today the heat is weak so much so that the windshield will not melt the ice . this is a common problem with these vehicles. first I would make sure no key in the lock cylinder. then remove the negative battery connection. then put key in and turn to run position and leave for 15 min. this will reset everything. then TAKE KEY OUT OF LOCK CYLINDER. connect the battery back up. see if it works properly.

    lets say it is still not hot then this would be the heat damper motor which is in the duct work at the hump. this you will see a cable feeding it. removal and cleaning may fix this as they stick[damper door sticks] or the plastic has distorted and now the motor shaft is binding.

    since your in a warmer area than I am my heater core is flushed out separately. hoses are removed at the engine and the heater core is flushed and blown out to removal all debris. even when it goes to zero deg F you get too hot to handle air. but you need it with snow/ice at these temps.

    the other reason weak no heat suddenly would be a damaged coolant system // leaks/air/frozen. do the air purge procedure to remove air . if this works but you loose heat again then you will need to fix what is causing the air to enter the coolant system.
    good luck

    - - - Updated - - -

    If this was flushed and the block not completely drained with the adding of 50% coolant mix it is possible it got frozen.

    anytime these engines are flushed and the engine not drained you only use 100% coolant because 2 gallons is trapped in the engine.

    with the extreme cold going far to the south I can see how many are with frozen engines...
  5. Jeff Dodson

    Jeff Dodson Member 1 Year

    Thanks, I will give those a try. As far as the flush, I would think the dealership would do it correctly, HOPEFULLY, as you stated the procedure. No problems with the coolant or engine getting hot or cold.....
  6. j cat

    j cat Epic Member 5+ Years 1000 Posts

    I would purchase a dexcool coolant tester . make sure they did have the proper amount of coolant antifreeze. should be -40 deg f.
  7. poncho62

    poncho62 Active Member 2 Years 100 Posts

    By any chance, is it just low on coolant?....From what you described, it sounds like it
  8. RayVoy

    RayVoy Epic Member 5+ Years 5000 Posts

    The needle on the temp gauge should be at 12 o'clock (pointing straight up). If it below 12 o'clock, the thermostat needs to be replaced.
  9. Jeff Dodson

    Jeff Dodson Member 1 Year

    That's where it is... I said 190-200 because it's not on the 210 mark
  10. RayVoy

    RayVoy Epic Member 5+ Years 5000 Posts

    Is not the 210 straight up (12 o'clock)?

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