02 Blazer overheats when heater on

My stepson claims his 2002 Blazer overheats only when the heater is turned on. So far I have flushed the heater core, it did not appear to be clogged up at
all.. My Clymer Manual is no help.
Last winter I drained, flushed system at about 80,000 due to heater not working and the dex-cool looked gummy. Flushed the heater core and solved problem. Replaced with fresh Dex-cool. This time the dex-cool looks ok.
Any ideas what the problem might be?
Thanks
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wrote:

I doubt the heater being on causes an overheat situation. Usually it is the opposite. It was probably coincidental. I'd check the thermostat then verify that the water pump is operating. I've heard of some with plastic impellers that had the impellers shear off internally and thus not pump. If this problem is intermittent, I'd concentrate on the thermostat. FWIW YMMV
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On Wed, 28 Dec 2005 16:51:09 -0500, NickySantoro

I agree. The boy says the temperature has been fine since 12/25 since he stopped usibg the heater. I will try to test drive it Saturday. Thanks for your reply
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turned on.

up at

working
problem.
Does the gauge go up instantly when the heater blower goes on?
Al
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I wouldnt have put dexcool back in the truck, I would have filled it with green but thats just me... I saw what dexcool did to my hoses, made the insides of them get all nasty and gummy feeling.

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Which is generally a sign of poor maintenance.
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wrote:

Is the gauge saying the engine is overheating or does he have any indication from the engine/radiator that the engine is overheating?
The only way I can figure this complaint is that some how the gauge is misreading the actual engine temperature.
--

Dave in Columbus

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On Thu, 29 Dec 2005 00:33:08 -0500, Dave in Columbus

The story is that the gauge went almost to the red and some coolant overflowed evidenced by the smell of coolant burning. Some type of discharge ? came out of the vents, the heater was turned off and temperature gauge returned to normal. Guage has been showing normal since then (12/25) with the heater on off. If the heater core is leaking the passenger floor would be wet, right? I will work on it Saturday. I plan to flush the Dex-Cool and replace with green stuff. Thanks for your reply.
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Check this out.
http://www.girardgibbs.com/dexcool.html

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