Q: Heater gets hot but then blows cold when idling or driving.

asked by on

heat gets hot then cold when idle or driving i have changed thermastate and new coolant

My car has 45000 miles.
My car has an automatic transmission.

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. To avoid any unnecessary repairs, I would still recommend having a certified expert, like one from YourMechanic, come to your location to diagnose your heater issue firsthand and make the right repair.

Was this answer helpful?
The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details
  1. Home
  2. Questions
  3. Heater gets hot but then blows cold when idling or driving.

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: Explorer leaking coolant.

I would return to where you had the radiator installed so they can check the radiator for leaks. It is possible that a hose clamp may have been left a little loose or something minor like that. It happens to...

Q: Weird smell from AC.

There is usually only two causes of this symptom. Inside your dash lies the evaporator for the air conditioning system. This evaporator looks like a small radiator but gets cold instead of hot. Imagine a soda can freshly opened out...

Q: Car heats up but only blows out cold air and the temp. Goes up then back down. Radiator is full of anti freeze

The engine temperature needs to be above 180 to 190 degrees before the thermostat opens and you will then have heated coolant flow to the heater core. If your engine does not keep a steady temperature then the thermostat may...

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...
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...
P2103 OBD-II Trouble Code: Throttle Actuator Control Motor Circuit High
P2103 means there is a fault with the throttle actuator control motor circuit, likely due to a defective electrical component or part.