Skip the auto shop - Our mechanics make house calls

Q: My heater used to warm up when the engine warmed up, but now it takes far longer and never gets half as a hot as it used to.

asked by on

Is this my heater core? Or my thermostat? The engine itself seems to come up to the middle of the temperature gauge, and it never overheats.

My car has 170000 miles.
My car has a manual transmission.

You may have a clogged heater core that may be prohibiting the outer linings of the heater core to get hot. As you know, the heater core is a series of tubes that the coolant runs through that generates the heat from the warm coolant after circulating through the motor. These tubes can occasionally develop a buildup on the inner walls such that when the heater core is "flushed" this buildup on the inner walls of the lines remains and still allows the coolant to flow through the heater core. It is important to note that when the heater core is "flushed" it is possible to get good flow through the heater core while the inside walls of the heater core remain caked with buildup. As a result, the buildup on the inner walls prevents the temperature from rising to its capability due to the insulating effect of this buildup on the inner walls which will prevent the necessary heat transfer to properly heat the inside of the car. I would recommend having an expert from YourMechanic come to your location to diagnose and replace your heater core.

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
  • My heater used to warm up when the engine warmed up, but now it takes far longer and never gets half as a hot as it used to.

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: Thank you

Check the wiring to the fuel pump and make sure that it is plugged in properly. The fuel pump will stop working if the wiring disconnects from the pump. If the wiring is connected properly, then the fuel pump relay...

Q: The clock in the car and light on the passenger airbag light

Hi there. Most of the time, the dimming and brightness of the dashboard lights are controlled by a switch on the vehicle's instrument panel or under the dash near the fuse box. In some cases, this dimming switch may become...

Q: Car stalled and now won't crank

No start conditions are complicated to diagnose sometimes because of all the variables. This is especially the case in this situation where we have very limited information about what the vehicle is doing besides not starting. Questions such as: is...

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...
Rules of the Road For Iowa Drivers
Driving on the roads requires knowledge of the rules, many of which are based on common sense and courtesy. However, even though you know the rules in...
P2428 OBD-II Trouble Code: Exhaust Gas Temperature Too High Bank 1
P2428 code definition A P2428 trouble code signifies that the PCM has detected a problem in the exhaust gas temperature sensor circuit in bank 1, which subsequently contains the number one...