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Heating problems with 1994 Toyota Corolla

I have a 1994 Toyota Corolla with a heating problem. The water pump and the thermostat had just been replaced. However, the engine overheating still remains a problem with the car. In addition to the overheating problem the interior heat works intermittingly: when the temperature control is set to max heat unheated air comes out the vent. What can be done to solve this problem?

Under what conditions does the engine overheat? Idling? Driving? Stop and go traffic?

Are the radiator fans working?

Are you sure there’s no air in the cooling system? Are you losing any coolant?

Are the hoses going to and from the heater core both hot after the engine warms up?

You might have a blend door problem (94s have vacuum control???). If my guess is right, you could have a loose or cracked vacuum hose to the heater box.

Have a mechanic sniff the air above the open radiator for combustion gases. If unburned hydrocarbons are detected suspect a leaking head gasket. IIRC, auto parts stores sell a chemical sniffer that will change color if the air exiting from the radiator contains combustion gasses so you could test yourself.

Hope my suspicion is incorrect.