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1999 GMC sierra no heat

This is a discussion on 1999 GMC sierra no heat within the Technical / Maintenance forums, part of the General Discussion category; ok my dad has a 1999 GMC1500 sierra and there is no heat. he said that one of the two ...

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    1999 GMC sierra no heat


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    ok my dad has a 1999 GMC1500 sierra and there is no heat. he said that one of the two heater hoses is hot the other is cold. so the coolant is obviously not flowing through. does anyone know what the problem could be?? thanks
    Last edited by JuniorLs1; 10-30-2005 at 12:39 PM.

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    Re: 1999 GMC sierra no heat

    Stuck thermostat. Good luck!

    Brian

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    Re: 1999 GMC sierra no heat

    It could be stuck thermostat but if the truck it running at normal temps I don't think so. Normally on the newer trucks temp control is all electrical. I maybe off the path b/c it's been awhile since I worked on a newer truck but I think they have a valve to control the colent for the heater core that maybe stuck. A suggestion would be to do a coolant flush on the heater core and see what comes out there also could be crude blocking it. Also can you smell a sweet smell in the cab of the truck if so the heater core could be leaking causing no heat. My moms winter rat a 94 blazer wasn't putting heat out but was coming up to temp. we were having engine problems and pulled the computer to have it checked and found that the heater core was leaking you couldn't smell the coolant b/c it cooling down b/4 it would steam. I hope thats some food for thought and helps you out.

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    Re: 1999 GMC sierra no heat

    thanks for the help guys!! the truck runs at normal temp and everything so that kinda made me rule out a stuck thermo, it does seem like like the problem could be something stuck in the heatercore?? since the hose that goes into the heatercore is hot and the one coming out is cold, i dont know if that is normal though on these trucks??

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    Re: 1999 GMC sierra no heat

    My wife`s blazer was doing the same thing, no heat/ hose return from heater core was cold. Thought it was plugged up but also did some searching on why the heater core goes bad. I couldn`t find anything on blockage. But what I did find out is, anytime there is air in the coolant system it most generally gets trapped at the heater core causing an air-lock. The way to get the coolant flowing again is fairly simple. First you start the engine and wait until it`s at operating temp. Then put some rags around the area of the return hose clamp area on the heater core. Loosen the clamp from the hose and twist and pull a little at a time until you see coolant flowing. Don`t pull it completely off and let it flow all over your engine. Just enough so you can feel the fluid running through the hose. Remember the coolant is plenty hot so be careful. The dealership wanted 1000.00 to replace the heater core.Ouch!! Hope this helps.

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    Re: 1999 GMC sierra no heat

    ok thanks alot!! i will give it a try and hopefully that is the problem.

 

 

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