Skip the auto shop - Our mechanics make house calls

Q: Overheating and heater not working

asked by on

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.

Was this answer helpful?

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

Was this answer helpful?

Need advice from certified mechanic? Get help now!

Over 1000 mechanics are ready to answer your question.
The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

Get an instant quote for your car

Our certified mechanics come to you ・Backed by 12-month, 12,000-mile guarantee・Fair and transparent pricing

Get a quote

What others are asking

Q: air conditioner not blowing air from dash vents, but blowing air from side vents

A few different items can cause the air to not blow out of the dash vents. The most common are a blend door or a control switch. The best method for the AC diagnosis feature can be found in the...

Q: Backfires around 70 mph and feels like gas might cut off at low speeds

Hello - fuel starvation or failing ignition could cause the behavior you are experiencing. If you accelerate from a standing start up a long hill, does the engine behave in the same way in each gear? Ignition problems will show...

Q: Starts runs for 30 sec. Shuts down.

Hello. This behavior suggests that the carburetor needle & seat are sticking, and the carb requires some adjustment and/or a rebuild. These fuel valve components allow fuel pressurized by the fuel pump into the carburetor float bowl (and from there...

Related articles

What Causes Hoses to Leak?
While the largest part of your engine is mechanical, hydraulics plays a significant role. You’ll find fluids at work in a number of different areas. Your car's fluids include: Engine oil Transmission...
P0240 OBD-II Trouble Code: Turbocharger Boost Sensor B Circuit Range/Performance
P0240 code definition Turbocharger Boost Sensor B Circuit Range/Performance What the P0240 code means P0240 is an OBD-II generic code triggered when the Engine Control Module (ECM) detects the intake boost...
How to Avoid Back Pain in a Car
If you have back problems, sitting in a car for an extended period of time can be excruciating. Even without back problems, you could experience discomfort and soreness from...