Heater Core


Heater Core

The heater core is a heat exchanger that serves to keep your passenger compartment warm as well as to protect your window glasses from ice and condensation build-up in cold weather conditions. Being a part of your engine cooling system, it acts just like your regular radiator, yet performs a different function. Unlike the radiator, the hot coolant that circulates through the heater core is used to warm up the cabin of the vehicle and to defrost your windows. To increase its efficiency, it works in tandem with the fan, which pushes air through the heater core, delivering warm air to where it is needed most.


Heater core failures are difficult to diagnose due to the specific location of the heater in the vehicle. It is placed under the dashboard, which makes it the only part in your vehicle that can leak into your cabin. As a rule, such leaks are difficult to diagnose since they are usually found under the carpet. Fortunately, this rarely happens with proper cooling system maintenance. If you replace the coolant at the time and mileage intervals provided by the manufacturer and flush the cooling system every time the coolant is refilled, you will prevent collecting rust, dirt and other particles inside the heater core which can damage it from the inside. 

Your heater core is a maintenance free part, which won’t draw your attention until a problem appears. If this happens, you should notice one or more of the following signs of a bad heater core:

It takes a lot of time to warm the cabin

If your engine doesn’t overheat during a long trip, yet your climate control system can’t warm up the car, you might have a bad heater core.

Before replacing the heater core, make sure it is the root of the problem. A thorough diagnosis of the entire heating system will help you find that out. First of all, check all related fuses, the heater core fan circuit and the fan. Then, you can make a simple test to check the blend door and the vents. Turn on your air conditioner at its max point and check whether cold air comes through the vents. If it does, switch to the heater mode to see if there is warm air flowing through the defrost and floor vents. If only one of the vents doesn’t work, you might have a bad blend door or the vent is clogged. In case none of them supply warm air, you should check the air filter because it can block airflow due to dirt or leaves.

If none of the steps provided above help, most likely your heater core is clogged. To inspect the heater core, you will need to remove the dashboard, which is a time-consuming task, so it is better to leave this job to a mechanic. He or she will visually inspect the heater core for signs of damage and leaks. If it looks fine, cleaning the exterior fins from junk and/or flushing out the heater core’s passages with some air or water at reasonable pressure can help for fixing the problem. Otherwise, you may need to replace the heater core with a brand-new part.

You smell coolant or notice it on the floor

Your coolant should have a sweet smell. If you notice it while driving the vehicle, you may have an interior coolant leak. Even if the leak is minute, it must be addressed as soon as possible to prevent engine overheating and other problems. 

You can’t defrost the windows, or they are fogging up

If a coolant leak is big enough to create a mist in the system, this coolant smoke can collect on your windshield. As a rule, it is messy to deal with and is harmful to your health.

Coolant leaks under the dashboard or on the carpet

Any signs of coolant under the dashboard or on the floor are an indicator of a coolant leak. If you notice it, don’t waste your time trying to fix it with stop-leak products. It’s better to call your mechanic for advice.

A low coolant level caused by a leaking heater core can lead to engine overheating. This is the worst-case scenario you should avoid. It is cheaper to replace a heater core and clean your carpet from coolant than to rebuild the engine.

Low coolant level and engine overheating

A damaged or rusted heater core can leak into the interior of the vehicle, resulting in a low coolant level and engine overheating. If you have to top it up on a regular basis and your temperature gauge runs high, you should get in touch with your mechanic or visit a repair facility.

Heater core troubleshooting and replacement

Your heater core is located under your dashboard, which is why both diagnosing and replacing it will involve a significant amount of labor. Your mechanic will need to disassemble the dashboard to access the core and reinstall everything back when the problem is fixed. This is a time-consuming and pricey job, which is why we recommend you to replace a bad heater core instead of trying to repair it. All heater core hoses and other related components must also be checked for damage and wear, and replaced if necessary.

Depending on the vehicle, you may need to recharge the air conditioning system which will significantly affect the final cost of the repair. Plus, if you have worn-out engine mounts, they can allow for erratic movements, causing damage to heater core hoses. To solve this issue, bad motor mounts must be replaced, which will also affect your repair bill.

Your heater core is best to fix in summer when you don’t need to warm the cabin or defrost the windows. If the estimated repair cost is high you may go with a temporary fix, having your heater core bypassed. This will require to disconnect both inlet and outlet heater core hoses and couple them together. But keep in mind that it is a temporary solution, so don’t forget to replace a damaged or worn-out heater core before winter comes.

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