Car Overheating At Slow Speeds

I have a Toyota corolla, and I just replaced the radiator and the thermostat. The engine wants to run hot at lower speeds and when I stop when I take off again it runs fine at 55 and above but it does not want to run hot at idle and in park.

My step father is a mechanic and we have pressure tested the cooling system and everything else I can think to do I have been working on cars all my life but this has me stumped.

Your input would be greatly appreciated thank you Chris.

Hi Chris,

I would first check the electric radiator cooling fan motor. I would suspect It is not coming on, so check that first.  Some non U.S. models older vehicles use an old fashion fan blade, so if you have one make sure the fan is sucking air across the radiator and that air should be HOT when the engine is running hot.

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It is electric and it is coming on I think it may be a blown head gasket because it is holding pressure on the radiator even after the car has cooled off for over 2 hours if you have any more info it will be greatly appreciated

Hello again Chris,

Well, holding some pressure is probably a good sign. If you had a head gasket or any kind of coolant leak the pressure would leak out, along with some coolant.

When the engine overheats turn on the heater and see if the air coming out of the ducts is hot. If the air is HOT, then there is hot coolant properly circulating throughout the heater core inside the dashboard.

If the air is COLD, or just Luke warm then I would suspect that there is not enough hot coolant circulating throughout the system.

An air pocket in the system that needs to be bled out would be the first step to take. Make sure you installed the correct temperature thermostat, should be 195 degrees.  Make sure the radiator cooling fan is coming on, and the air that is being drawn across the radiator should be hot air, not cold.

If that air is cold, there is a restriction or air pocket in the system somewhere. Both upper and lower radiator hoses should be hot when the engine is at normal operating temp.

Last thing to look at would be to manually check the temperature of the engine when the gauge says it is overheating. This could be a gauge problem or a temperature sending unit not sending the proper temperature to the gauge and the engine is not overheating at all.

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Austin Davis