Skip the auto shop - Our mechanics make house calls

Q: Temperature spiking up after I changed my thermostat trying to get my heater to work.

asked by on

There was nothing wrong with the original thermostat but I wanted to start at step one to see why my heater was not getting hot. I changed out the thermostat and after about 20 minutes of driving the temperature starting rising. I had the radiator flushed thinking I had some air in the lines. After that didn't work I put the original thermostat back in because it had no issues. The temperature is doing the same thing now, what could be the problem? Also nothing is leaking!!

My car has 134000 miles.
My car has an automatic transmission.

A: The heater not working in some cases may be...

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 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.

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?

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

Ask a Mechanic
(100% Free)

Have a car question? Get free advice from our top-rated mechanics.

Ask A Mechanic
Over 10,000 questions answered!

Get an instant quote for your car

Our certified mechanics come to you ・Backed by 12-month, 12,000-mile guarantee・Save up to 30%

Get a quote

What others are asking

Q: My car over heated

The first thing to do is to remove the serpentine belt off the engine and see if you feel the water pump pulley move around and if it does not turn very good. The water pump may be bad. ...

Q: Car over heating

If there are no leaks and no blockage in the system or problems with the cooling fan, then you may have a water pump that has worn impellers that may need to be replaced. I would recommend having the car...

Q: My Alignment and Brake mechanic, says I need motor mount replacement.

This is definitely a sure sign of broken motor mounts. As you may have noticed the torque of the engine causes it to rise when shifting in or out of gear when a motor mount is not securely holding the...

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...
P0052 OBD-II Trouble Code: HO2S Heater Control Circuit High (Bank 2 Sensor 1)
P0052 code definition HO2S Heater Control Circuit High (Bank 2 Sensor 1) What the P0052 code means This code is seen when the Engine Control Module (ECM) tries to control the...
How Much Does a Mechanic Make in Vermont?
Automotive technician jobs in Vermont have an average mechanic salary of $37k, with some mechanics earning a salary of $53k.