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