A heater core is an automotive component that uses hot coolant to project heated air into the car’s cabin. Also known as a heater matrix, it functions as a mini radiator. When you turn on the heater inside your car’s cabin, a valve opens so that coolant gets directed from the engine to the heater core. As the hot coolant travels through the heater core, a fan blows air over the core’s fins. That produces hot air that’s projected through the vents inside your car’s cabin.
Does a Heater Core Fail?
No automotive component lasts forever, though, and heater cores are no exception. It’s not uncommon for heater cores to fail after about 10 to 15 years; with a neglected coolant system, failure can occur even sooner. Unfortunately, diagnosis isn’t always easy. Because the heater core typically is behind the passenger-side firewall, you can’t see it without taking apart the dashboard and other surrounding components. But there are a few signs you can look for that indicate a failed or failing heater core.
What symptoms can indicate a failed heater core?
Condensation on Windows
It’s normal for condensation to appear on the inside of your car’s windows. That typically occurs when the air outside your car is colder than the air inside the vehicle. The temperature nuances between these two environments cause moisture to settle on the inside of your windows, resulting in fog. Turning on the cabin heater or defroster should eliminate condensation on your windows — but only if the heater core is functioning correctly. If your heater core is ruptured, pressurized coolant will escape when you turn on the heater or defroster. The coolant-filled air will then enter your car’s cabin where it causes condensation to form on the windows.
Wet Passenger-Side Floorboard
A wet passenger-side floorboard may also indicate a leaking heater core, the most common type of failure. Coolant will drip down behind the passenger-side firewall, some of which may leak through the firewall and onto the floorboard. A failed air-conditioner evaporator core can cause a wet passenger-side floorboard as well. The difference, however, is that a faulty heater core will leave your passenger-side floorboard covered in coolant, whereas a failed evaporator core leaks water onto the floor.
Low Coolant Level in Radiator
Your car’s radiator should remain full of coolant. If you discover the coolant level is low one day, you may have a leaking heater core. When you run the heater or defroster in your car, coolant travels through both the heater core and radiator. That means that a ruptured heater core will cause coolant leak out, resulting in a low coolant level in your radiator.
Keep in mind that you should only check your radiator’s coolant level when the engine is completely cold. Removing the radiator cap on a hot engine can spray 200-degree pressurized coolant onto your skin, so wait until the engine has completed cooled off. For added protection against injury, cover the radiator cap with a towel and turn slowly to remove it.
Room-Temperature Air Coming Out Vents
If you turn on the heater and discover room-temperature air coming out the vents, you may need to replace your heater core. There are two primary components responsible for producing heat inside your car’s cabin: the blower motor and the heater core. The blower motor is a small fan that blows air through the vents and into your car’s cabin.
The heater core, on the other hand, is a miniature radiator with columns of tubes through which hot coolant flows. If the blower motor has failed, you won’t feel any air coming out your vents. However, if the heater core has failed, but the blower motor still works, you may feel room-temperature air coming out the vents.
Room-temperature air occurs when there’s little or no coolant flowing through the heater core, which is usually the result of a leaking heater core. The blower motor will still force air into your car’s cabin, but without hot coolant flowing through the heater core, it won’t produce hot air. Instead, the air will feel room temperature or just slightly warmer.
Sweet Smell Inside Cabin
Even if your passenger-side floorboard is dry and the windows aren’t fogging up, you may notice a sweet smell inside your car’s cabin when the heater core leaks. The main ingredient in the coolant is an organic compound called ethylene glycol, and the vapors of this compound have a unique sweet odor that lingers in the air. If your heater core has a pinhole leak, a small amount of coolant may leak into your car’s cabin. It may not be enough to cause moisture on the floorboard or windows. Instead, the only sign of this leak is a sweet smell.
Engine Is Overheating
Because the heater core is part of your car’s cooling system, failure of this component can cause your engine to overheat. That occurs in one of two ways. First, a leaking heater core will lose coolant, reducing the amount of heat that’s released by the radiator. Second, a clogged heater core will restrict the flow of coolant through your car’s cooling system, also reducing the amount of heat that’s released by the radiator. When either of these scenarios occurs, the engine will heat up to dangerous temperatures, at which point you should see the temperature needle on your dashboard climb into the red zone.
What Should I Do If My Heater Core Has Failed?
If you believe that your car’s heater core has failed, you should replace it as soon as possible. Aside from the brutally cold cabin interior that you’ll have to endure during the winter, a faulty core can cause your car’s engine to overheat, which can lead to severe damage. Some engines are more resistant to heat-related damage, but they all can experience blown gaskets, warpage or cracks when exposed to enough heat. By replacing your failed heater core, you can avoid these costly problems and enjoy a comfortable cabin when driving during the winter.