Signs That Your Car Has a Bad Heater Core

One of the worst problems you can have with an older car is a leaking heater core. Not only will the interior of your vehicle get wet and smell bad, just wait until you get an estimate to repair it. Many estimates come in well over $1000. Yikes.

In this article, we will discuss heater cores, what they do, where they are in your car and why on earth they are so much to repair.

What Is a Heater Core?

A heater core is a miniature version of your radiator and is part of your engines cooling system. If you look at one, it looks exactly like a small radiator with a grid of little tubes bridged by fins that disperse heat.

What Does a Heater Core Do?

Your radiator system pumps hot coolant through the tubes in a heater core and this causes the core to become very hot. Air is then blown through the core and used to heat your car in the winter and to defrost your windshield.

Where Is the Heater Core Located?

Your heater core is usually behind your dashboard, under the center or the passenger side. It will have some sort of casing or housing and is usually buried behind almost every other component of the dashboard. This is precisely why they are so expensive to repair, to just get at your standard heater core may require hours and hours of work.

Why do They Go Bad?

According to our experts at Metro Kia of Atlanta, a local Kia dealer in Atlanta, GA, heater cores go bad because of corrosion, in particular because of electrolysis corrosion. Electrolysis corrosion is a chemical reaction that occurs between a car’s coolant and the metal surfaces within a car’s cooling system.  A typical cooling system, for example, will involve an iron engine block, an aluminum radiator, and an aluminum heater core.  Because of these different metals being immersed in the same water path, a matter of electrophysical chemistry occurs; small electric currents will flow between the different metal surfaces.  The result of this current flow over time is a corrosion that will eat away at the metals, which will eventually cause holes and leaks.

How Do I Know If My Heater Core Has Gone Bad?

Internal Fog – The most common tipoff to a problem with a heater core is when the inside of your car suddenly fogs up for no reason. What may have happened is that your heater core sprung a leak while you are driving, after the engine warmed up.

What’s that smell – An unmistakable sign of a leaking heater is a fruity, smell inside the car. This is the smell of the ethylene glycol antifreeze in your coolant and definitely a sign that your heater core is leaking.

You are losing radiator fluid – If you find your car, truck, or van has suddenly developed a voracious appetite for coolant, and you cannot figure out where it’s all going, you may well be looking at a blown heater core. Check the floor of your car for wetness, especially near the front passenger seat.

It’s Cold in Here – A chilly passenger compartment is not always a sign of a faulty heater core. It may indicate that your blower motor or another component of your heater has gone bad. Though if you’re seeing one of the other signs in addition to a lack of heat, that’s a pretty good indicator that the heater core itself has a problem.


By the way, there is a way to keep your heater core in good operational shape. Make sure and use good quality anti-freeze at all times. Anti-freeze contains corrosion inhibitors that will prevent electrolysis from occuring.

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