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Q: My vehicle is taking a very long time to reach normal operating temp. and then over heats.

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I had a coolant leak from the upper coolant hose on the radiator and before I was able to fix it my ex boyfriend opend the coolant reservoir while the car was running. As soon as I drove it after that the car began to over heat. I have currently changed the radiator , thermostat and the water pump. All one after the other with very little driving in between and the car is still overheating. I have burped the system for air I am now at a loss. The fans turn on when the car reaches normal opeating temp as well.

My car has 135000 miles.
My car has an automatic transmission.

A: Hello. I assume you have also replaced the ...

Hello. I assume you have also replaced the leaking upper radiator hose. If you haven’t, this must be done as well. Opening the coolant reservoir didn’t create the condition you have, so rest assured there. Cooling systems are not as simple as one might think. There are several misconceptions about them. Two things come to mind in your situation.

Number one, is the thermostat installed correctly or has it failed? New thermostats can fail. To test thermostat operation thoroughly, you need a infrared temperature gun and some patience. You will be monitoring the temperature at the thermostat housing. Once the housing reaches around 200 degrees Fahrenheit, the thermostat should be open and the upper radiator hose should be hot. If the thermostat housing is above 200 degrees and the upper radiator hose is still cold, or much colder than 200 degrees, there is a stat problem.

Second, it is possible you didn’t repair your leak soon enough and the head gaskets have been damaged. This is harder to diagnose and is best done with a hydrocarbon detector. There is also a kit that uses a liquid solution but it can be dangerous and difficult to use.

If you drove the car too long with low coolant, I would suspect a head gasket problem. Blown head gaskets, as they are known, will continually create more bubbles in the cooling system. No matter how many times you bleed it, there will be bubbles. These bubbles are made of hydrocarbons created in the combustion process in the cylinders. With this situation, even the thermostat check could be false because if there is an air bubble behind the thermostat, it will not be able to regulate the coolant temperature correctly.

Diagnosing cooling systems correctly takes time, patience and experience. They are not as simple as they are thought to be when things go wrong. There are a few other possibilities, but I think you covered those by replacing the radiator and water pump. If you still need help, contact a professional mechanic, such as one from YourMechanic, who can diagnose your vehicle’s heating issues.

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