When you turn on the heat in your vehicle's cabin, you expect warm air to come out of the vents. Nearly all modern-day devices are equipped with a climate-controlled cabin. They feature an air conditioning system to create cool air and a heater core to create warm air. A leaking heater core, though, may not work as intended. How do you know if your vehicle's heater core is leaking exactly?
#1) Damp Floorboard
A leaking heater core may result in a damp floorboard. Heater cores contain coolant. They work by blowing air over the hot coolant. As the hot coolant travels through the heater core, a fan will blow air over it. This creates warm air that's expelled out the vents and into the cabin. Since most heater cores are installed behind the passenger-side dashboard, a leaking heater core can result in a damp floorboard. Coolant will leak out of the heater core, after which it will drop down onto the passenger-side floorboard.
#2) Window Condensation
Window condensation is a common sign of a leaking heater core. While there are different varieties of coolant, most consist of a mixture of distilled water and antifreeze. Coolant will leak out of the heater core and onto the floorboard where it will accumulate. All of this moisture will then manifest in the form of window condensation. You may notice condensation or "fog" on the interior side of your vehicle's windows if you're dealing with a leaking heater core.
#3) Sweet Smell
If you smell something sweet when driving -- or when walking around your vehicle's exterior -- the heater core could be leaking. Coolant has a distinct sweet smell. This is due to the antifreeze used to raise its freezing point. Antifreeze consists of ethylene glycol, which has a naturally sweet smell. If your vehicle has a leaking heater core, sweet-smelling coolant will escape it.
#4) Loss of Cabin Heat
Of course, you may experience a loss of cabin heat if your vehicle has a leaking heater core. Heater cores require coolant to produce warm air. Coolant will pick up heat from the engine, after which it will flow through the heater core where a fan releases the heat. In the event of a leak, there may not be enough coolant to produce warm air for your vehicle's cabin.
#5) Overheating Engine
Hopefully this doesn't occur, but a leaking heater core can cause engines to overheat. Coolant isn't used exclusively to warm cabins; it's used to cool engines. And engine cooling systems are connected to heater cores. Therefore, a leaking heater core can interfere with your vehicle's cooling system, potentially causing the engine to overheat.