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Volvo overheating issue

I own a 86 Volvo 740 GLE and when I turn on the fan for heat I get cold air and the temperature gauge begins to climb and will go all the way to the right. The thing is the engine is not getting hot and cold air continues to come out until the needle goes back to center.

I wait for the gauge to go to center and do not turn on the fan until I have gone 2 miles (the amount of time it normally takes for the air to get warm) and nothing happens until I turn the fan on.



Nothing else happens, the car runs the same, the noises are the same and the engine is not getting hot, so the car is not actually overheating.

The water pump and thermostat have been replaced, the thermostat just this past weekend. The coolant is filled, the oil was replaced a month ago.

Any ideas?

It sounds like there’s air trapped in the cooling system.

Try this. Get the engine up to operating temperature, and with the engine idling, slightly loosen the upper radiator hose clamp. Take a flat bladed screwdriver and slip the tip between the upper radiator hose and the radiator hose neck until all the air has been purged out of the cooling system. Retighten the hose clamp.

Tester

So the gauge responds when you turn the fan on and off? I think there’s a bad ground connection involving the gauge cluster and the fan circuit.