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post #1 of (permalink) Old 11-26-2003, 12:27 PM
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heater problem

I have a 96 3/4 ton suburban with dual heat/ac. I live in MN so I need the heater. I start the truck and it warms up to about 210 degrees and I get heat, but at no particular point in time the heat quits and it blows cold air. when it does blow heat it is very hot and I need to turn down the blower. why is it doing this? I checked the coolant and it is full in the radiator and the overflow. The engin doesn't overheat. I thought it might be the heater core, but the rear heat does the same thing. Do both heater cores go out at once? doesn't seem likely. the truck has 110,000 miles and the cost to get a new heater core installed in the front is $600-900. Please help me.
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post #2 of (permalink) Old 11-26-2003, 12:47 PM
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Re: heater problem

have you tried flushing out the coolant system? maybe there is some junk in there and its blocking up the system somehow... worth a shot...
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post #3 of (permalink) Old 11-26-2003, 01:39 PM
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Re: heater problem

After it starts blowing cold, does it stay cold or does the heat come back? Maybe you have a bad or sticky thermostat. You may get heat initially and then the thermostat opens mixing the hot block coolant with the cold rad coolant, causing the heat loss. Did you try a rad cover during the winter to tame down the cooling during frosty weather? I have a 94 3/4 pickup and install a higher temp thermostat during the winter.
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post #4 of (permalink) Old 11-26-2003, 02:45 PM
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Re: heater problem

I will be flushing out the system tonight and trying to flush it out every way possible, the only thing I can think of is that there is something blocking the coolant in the heater hoses, because everything else works. Once the heat quits, it does not return until I shut off the truck and let it sit, then I can restart it in say 1-2 hours and it will have heat again. the only thing I can think of is that there is something blocking the flow of coolant in the heater hose and that it "settles" once the pressure is reduced once the engine/water pump has stopped.
post #5 of (permalink) Old 11-27-2003, 10:46 AM
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Re: heater problem

be aware of the fact that in the 96model year GM was using dex-cool coolant. do not mix the gree ethylene glycol and the dex-cool together. when they mix the fluid will solidify. its worse if you add green to orange than the other way around. i see it on a nearly daily basis. people come into the shop and say "i had low coolant so i topped it off and now a few weeks later i dont have heat and the light thingy is on"
every time, you see a brown putty i nthe radiator. if you flush the system VERY well you can convert to the green coolant. this is what i have done i nthe past on my vortec series engines. thegreen stuff is cheaper and much easier to locate
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