My 1986 Cadi Suville red engine light comes on while driving. Upon the engine overheating my overflow tank is scrouching hot and boiling. The coolent in the raditor is alright and the radiator is normal. I’ve replaced the heater cord, thermostat and fan control switch. Once the engine cools down and I pour some coolent in the overflow tank it rides alright on the freeway traveling at speeds under 60 miles per hour. However in stop and go traffic around town it will heat up quicker and my overflow will once again heat up and boil over.
Well, the coolant in your overflow tank is coming from the radiator. I would start by replacing the radiator cap and see if that helps. The car’s cooling system relies on pressure to raise the boiling point of the coolant, and without a good radiator cap, the car will overheat and boil over.
However in stop and go traffic around town it will heat up quicker and my overflow will once again heat up and boil over.
That sounds like the radiator fan is not functioning.
Next time this happens, check to be sure your cooling fan(s) are running. They should be. When the engine is cool, remove the radiator cap and check to be sure the radiator is full to the brim.