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When Should I Consider a Heater Core Replacement?

Consider a heater core replacement when you notice your car's cabin isn't warming up, there's a sweet smell indicating coolant leakage, or your windows fog without a clear reason. These signs suggest your heater core may be failing. Ready to ensure your drives are comfortably warm and safe? Let's explore the importance of timely heater core maintenance.
Lori Kilchermann
Lori Kilchermann

If the windshield in a vehicle fogs up when the engine starts, it is time to consider a heater core replacement. Another sure sign that a vehicle is in need of a new heater core is a wet passenger side front floor board. Coolant often leaks from a broken or bad heater core. A hint of warm antifreeze aroma as a vehicle is running or directly after it's shut off is another sign of needing a new heater core. Perhaps the most overlooked sign of a required heater core replacement is simply a heater that fails to give off heat when the blower motor is switched to high.

In vehicles that are liquid cooled, the hot coolant is passed through a small radiator-type component called a heater core. An electrical blower draws air through the heater core and blows the warm air into the vehicle's passenger compartment. Occasionally this unit will develop a problem in the form of a leak or a plugged coolant passage. When this happens it is time for a heater core replacement. Older heater core units were made of brass and more difficult to damage; newer units, however, are manufactured from aluminum and plastic, requiring great care to avoid damaging the device when installing it.

If the heater core is inside a heater box, you'll need to look around the engine compartment for the box.
If the heater core is inside a heater box, you'll need to look around the engine compartment for the box.

Vibration as well as continued cold to hot temperature cycling can cause the heater core to develop a leak. The most common area where a heater core will leak is at the input and output lines where the rubber heater hoses connect to the heater core. This leak can come as a large leak that soaks the carpet on the front floorboards or as a subtle leak that simply remains in the heater ducting and fogs the windshield upon engine start up. In either case, the first sign of a leaky heater core signals that it is time for a heater core replacement.

While heater core replacement is not a difficult task, it can often be tricky to place the heater core in its proper mounting location. It is for this reason that many shade-tree mechanics take their vehicles to a professional garage for heater core replacement. These professional mechanics typically have access to specialty tools that make the job of replacing a heater core much simpler. With knowledge of a particular manufacturer's method of installing the original heater core, the mechanic is able to understand the proper sequence of parts to remove to make installation of a replacement heater core a much easier task.

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Discussion Comments


@Logicfest -- Good point and that is the best way to tell if your heater core is going out. If you know you should have heat and you have none, then the heater core is definitely out. The best thing to do is check the temperature gauge, turn on the heat and wait until the engine is out of the "cold" zone to see if your heater works.

What a lot of people don't understand is that the heat you get in your car is essentially generated from your antifreeze. When the antifreeze heats up, your heater will work and will only blow cold air when your coolant is cold.


A foggy windshield is not necessarily a sign that you need to start thinking about a new heater core. It is common for a window to fog up when a car is tarted and the defrost is first turned in when you are in a very humid climate.

If that fog doesn't vanish when the engine warms enough for heat to come through the defrosting vents, then you do need to think about a new heater core.

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    • If the heater core is inside a heater box, you'll need to look around the engine compartment for the box.
      By: vicky
      If the heater core is inside a heater box, you'll need to look around the engine compartment for the box.