BobbyG453

I have a 2002 Honda Civic EX with 180k miles. No problems until 3 days ago. It overheated on the 45 degree morning. I stopped and had car towed. I changed T-Stat, Honda OEM, it ran great until I turned heat on, turned temperature ****, then it began to overheats - not all to red but close. I turned heat off and turned AC on to have both fans working and everything returned to normal. I have replaced radiator cap, checked oil, checked exhaust, everything to mark off blown head gasket and radiator problems. I am looking at heater control valve, will replace and flush heater core. Am I on right track or is there something else I need to check. I believe it may be the water pump, pump vanes may be worn . Could someone give advice, I believe that water is not flowing when I activate the heater, is there a switch/valve that controls that? Am trying to pull wiring diagrams so I can verify. I am an EEby trade, retired now, but I am not very good with cars. Can understand if I know how it is controlled, so please advise me.

Wankenstein

With Honda engines the most telling sign of a head gasket breach is loss of coolant in radiator and coolant gain/overflow in reservoir. Most of the other symptoms associated with a blown head gaskets don't usually present themselves with these engines.

Typically engaging the heater (climate control) will lower temp during overheat. My guess is the coolant was already low and when you engaged the heater and the water outlet valve opened it brought the coolant level in the cylinder head down further to a dangerous level and caused the overheat.