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Q: Overheating and heater not working

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My car is randomly overheating. Not all the time. When the engine temp rises, the heat inside gets colder. If the heat inside gets hot again, the engine temp goes down. Radiator was replaced. No o th er issues, as far as I know.

My car has 116000 miles.
My car has an automatic transmission.

The heater not working in some cases may be related to the overheating problem you are also having. This may be due to a faulty heater blower motor or potentially a bad heater core. As you may know, the heater core is a small radiator like unit that circulates the hot coolant from the engine through the heater core which then uses this warm coolant to heat the inside of the car with the help of the blower motor that blows the warm air through the vents inside the car. When the cooling system is not properly circulating coolant through the motor, this results in the warm coolant not being pumped through the heater core properly in order to warm the inside of the vehicle. In some cases there may be air pockets in the heater core which can cause the heating of the inside of the vehicle to fluctuate between warm and cool air erratically.

Engine overheating can be caused by a number of things such as low coolant levels, a faulty thermostat, or a failing coolant fan switch. As you may know the coolant fan switch helps to maintain the proper coolant temperature by turning on and off at specific temperature thresholds. When this switch is not working properly, this can cause the fans to come on intermittently, all the time or sometimes not at all. When this happens you will notice a temperature spike and drop occasionally as the fan comes on and off. When your thermostat is not working properly or is stuck closed, this will not allow the coolant to properly circulate through the engine, which may cause the engine temperature to fluctuate erratically or in some cases just remain hot. As mentioned above, this also restricts the warm coolant from flowing through the heater core which uses this to blow warm air into the cab of the vehicle. I would suggest having an expert from Your Mechanic come to your home to diagnose your cooling system.

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Hello. It sounds like you have an air pocket caught up in your coolant system. Anytime a radiator is replaced air will be let inside of the coolant system and must be bled out because it is a liquid-based pressurized system. Air pockets in the cooling system will cause the vehicle to overheat and the interior heat to fade until the air pocket passes. But being the coolant system is circulatory the air pocket will return and cause the same symptoms again, until it is bled out. I suggest you have a technician pressure test your coolant system for leaks to make sure the air is not coming from other sources and to bleed the existing air out. A great way to find a technician to do so is here https://www.yourmechanic.com/services/car-is-overheating-inspection

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