Skip the auto shop - Our mechanics make house calls

Q: My heater seems to blow hotter when I'm driving versus when it's sitting at idle or at a stop light. Also the heater takes too long to heat up the cabin department. Why?

asked by on

When heating my car up in the mornings the heater doesn't get to it's full warmth until I start driving. Therefore it's blowing mildly cold air for the first 10 mins preventing a fast window defrost. I've made sure the coolant (50/50 mix) is filled to the line. First time experiencing this.

My car has 90000 miles.
My car has an automatic transmission.

A: Hi there. When your vehicle is in motion a...

Hi there. When your vehicle is in motion and driving down the road, then engine coolant temperature tends to get hotter on the engine before it gets to the radiator, so the heater will naturally heat up more when driving around. As far as the heater not heating up fast in the car, either the engine coolant is not hot enough yet to heat up the car or there is an issue with the heating system or cooling system in the vehicle. First check the engine coolant to make sure that its full. Top off the coolant if its low. Then check the heater control valve and see if its opening up when the temperature is at operating temperature. If the valve is not opening up, check the vacuum hose to it for any leaks. If nothing is found on the valve, then the valve needs replaced. If the valve is working correctly, then the thermostat may be sticking open when the engine coolant is cold.

The thermostat’s job is to bring the engine to operating temperature in a timely manner. If the thermostat is sticking open, then the engine not only will have a longer time to warm up the coolant, but the computer system will think that the engine is cold all the time and make the fuel system go full rich all the time. This will give the vehicle a poor fuel mileage and a waiting time for the heater. In this case, the thermostat would need replaced. If you need further assistance with your vehicle, then seek out a professional, such as one from YourMechanic, to help you with your heater not heating up in a timely manner.

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・Fair and transparent pricing

Get a quote

What others are asking

Q: I need to know the purge valve solenoid location and how long it takes to replace it.

Hi there. There are two different locations that the purge valve was located at, depending on the vehicle type. The first location would be on the engine intake next to the throttle body on the left side when viewing the...

Q: Car wouldn't go over 50 mph I went over and next thing you know I hear loud knocking from the engine

The knocking is suggestive of a mechanical failure of some sort. I would first measure cylinder compression to get a basic idea of the condition of the engine. If it doesn't test well (too low and/or too much variance) you...

Q: The air conditioner and heater control panel has no power, no lights, nothing

Since you seem to get some temporary action by messing with the fuses, the problem may lie in the power distribution box. Underneath the fuse panel is a network of connections, some of which may overheat in an older car....

Related articles

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...
What are the Car Pool Rules in Hawaii?
Hawaii is widely regarded as a land of vacation and relaxation, and as such, its scenic roads and routes are far better known than the state’s freeways. But, as with all...