what would cuase an 92 s10 to over heat when the heater is on but stay cool with out the heater running.
my husband has a 92 s10. its low mileage and everything but recently been having issues. when he turns on the heat it starts to over heat but when he turns off the heat its doesn't over heat.
That typically has the opposite effect. Is he turning it on defrost? That will kick on the ac compressor. Coolant is always flowing through the heater core no matter what position. All you change by moving the heater lever is a blend door behind the dash. If the ac is kicking on it cold be a bad fan clutch, partially clogged radiator, or numerous other cooling system problems
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