Skip the auto shop - Our mechanics make house calls

Q: Heater blowing lukewarm air. Had thermostat and gasket changed plus heater core back flushed. No change.

asked by on

What else would cause this problem? The work was done at a reputable mechanical shop so I am assuming they would make sure there were no air locks and coolant is full.

My car has 92700 miles.
My car has an automatic transmission.

The heater is reliant on the engine temperature getting up to and maintaining normal operating temperature. Once this is verified then you can check both heater hoses in and out of heater core with blower on low speed and heater on full hot. The two hoses should be hot and close to same temperature. Then put blower on high speed and check temperature out of vents and check both hoses again. The temperature of inlet hose will be hot and out let hose lower temperature since blower is on high. If you have good temperature of engine then heater core flow or air flow is not good. The temperature blend door actuator and core fins blockage are the most common causes of the problem.

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!
  • Home
  • Questions
  • Heater blowing lukewarm air. Had thermostat and gasket changed plus heater core back flushed. No change.

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: Engine light came on saying transmission system malfunction.

Hi there. The code is coming up for the torque converter clutch (TCC) is not working. Check the TCC fuse and see if it has blown. If the fuse is good, then the solenoid on the transmission that controls the...

Q: Grinding noise in park truck wont move

Hello there, there are a few possible cases for the truck to stop while driving like this. You did not mention if the grinding noise is in all the gears or just park. The most common would be a transmission...

Q: Idle high at start up then drops down slowly

Hi there. Typically when an engine starts up for the first time, the engine's RPM speed will be increased slightly to allow the motor and other operating systems to warm up to operating temperature sooner. In some cases, a vacuum...

Related articles

How Long Does a Heater Control Valve Last?
Keeping the right amount of coolant in a car is essential in keeping the engine at the right temperature. Failing to have the right amount of coolant or even bad elements...
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...
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.