Question about 1999 Chevrolet Silverado 2500

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1999 Chevy No Heat, and Overheating.

I own a 1999 Chevy Silverado, 5.3 L V8. I have no heat, and my truck over heats. I recently replaced the thermostat, and flushed the system, running water through the heater core and checking the flow of water through the whole system. I have let the air pockets out, and have kept an eye on the coolant level after draining it for the fourth time in two weeks. I know its a new thermostat (i boiled it) and i know the heater core is not clogged. My only thing left is to replace the water pump but i can't see spending the time or money when it seems to be operating, I have ran it with the supply to the core off and seen that it pushes water through the system. I cant find any crinks or crushed hoses and there is no leak that has appeared to me yet.

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  • derikoverhol Feb 13, 2009

    I forgot to add, its a 1500, not a 2500.

  • derikoverhol Feb 13, 2009

    Yeah, it overheated before replacing the thermostat. i keep coming back to the air pocket to. but i keep working with it and i really am starting to think something else

  • derikoverhol Feb 13, 2009

    white smoke from the tailpipe, its been cold so i thought that was normal till i noticed more than usual today when it was idle and its almost sixty, moisture does drip from it as well. Yes the hoses get hot, the lower and upper one to the pump, and the two through the radiator, one to the core also, the other coming from the core gets warm but not as much as the other. as far as water in the head, i dont know, i will have to check that.

  • Mark Egan May 11, 2010

    White smoke, and steam, look nearly the same from the tailpipe until the engine and exhaust system is warmed up. Water will also drip as the steam condenses in the exhaust system until it warms up. And water is a byproduct of combustion in a gasoline engine.

    So, the key thing is to figure out if the thermostat is causing the overheating, and to do that, pull the stat, then drive around. If you don't overheat, then you've proven the cooling system. Replace the stat. If it still heats up, then you've got a fan clutch problem, radiator problem, or not enough coolant.

    Not enough coolant is pretty easy. Just check it. Note if there is significant pressure in the radiator that would suggest a compression leak through the head gasket. Remember, a bad head gasket will pressurize the cooling system on the compression stroke, and **** in some water on a suction stroke.

    If your chasing an air bubble, then it's easy to get rid of. If the engine is cool, take the radiator cap off, start the engine, and wait for the thermostat to open. You can tell when it does, because the water level in the radiator will drop. Fill until you can fill no more. Put the cap on, fill the reservoir, and test drive.

  • James Bradburn
    James Bradburn May 11, 2010

    Are you getting coolent inside the head?
    Is there excess water coming from the tailpipe, or a white smoke?
    When it runs hot do you get nothing but steam from the bleed off?
    Is the lower hose that runs to the water pump hot or cold after driving speed?

  • Mark Egan May 11, 2010

    Sounds like it could be the fan clutch if it's overheating, but that doesn't make sense about no heat.

    Take the thermostat out and run the engine without it. If it still overheats, you either have a plugged radiator (water or air side) or a bad fan clutch. I am betting the fan clutch.

    Let's get that one fixed before we go to the next.

  • Dave Matthews
    Dave Matthews Jan 21, 2013

    I say you got a hose that collapses when it gets to normal operating temperture, They tend to do that when a hose goes bad...e



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  • 56 Answers

Did it over heat before the therm? if not it is the wrong therm. Other than that you have to have a air pocket.

Posted on Feb 13, 2009

  • David Fagan
    David Fagan Oct 30, 2016

    if not wrong thermostat, may have installed upside down

  • David Fagan
    David Fagan Oct 30, 2016

    always spring down, bell up



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After replacing the thermostat, you must bleed the air from the cooling system.

To bleed air from the 2.2L and 2.5L engines, remove the plug or sensor on the top of the thermostat housing. Fill the radiator with coolant until the coolant comes out the hole. Since the plug is made out of steel and the thermostat housing is aluminum, it is a good idea to apply an anti-seizing compound or Teflon® tape on the plug threads prior to installation. Install the plug and continue to fill the radiator. This will vent all trapped air from the engine.

Any trapped air in the heating system will have to be displaced by coolant. Once the cooling system is filled, with the radiator cap off, turn of the heater at it's highest setting. Start the engine and allow it to reach operating temp. You should see a drop in the coolant level as the air in the heating system is displaced by coolant. Add coolant to the proper level and replace the radiator cap.

Keep a close eye on the coolant level for at least the next couple of weeks. The cooling system is a "closed" system. Any significant decrease in coolant level indicates a problem.

If you have any questions, let me know.

Please take the time to rate this solution.

Drive safe and be warm.


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No heat !!! just blows cold air. I think it might be the thermostat. Where is that located on a 1999 Silverado? It is the small V8

could be the heater core valve, check the cable that opens and closes the water valve to the heater core.

check also the setting of the temperature level. it could still be set to cold.

wait for a few minutes for the water to heat up on the radiator. you could have tested it after you start the car and the engine is still cold.

tnx 4 using fixya,


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