I bought a 99 Cadillac STS that has overheated a couple times,but when I turn heater on high it cools to normal..any suggestions as to what it may be since it don't when the heat is on high????
Could be the heater core is adding the necessary coolant to bring the temperature down to normal.
Bad thermostat mine did the same thing. While your car is running grab your radiator hose if you can't squeeze it. Then it's the thermostate I changed mine in like 10 minutes very easy job to do.
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