Common signs that a heater core requires replacement include a lack of heat, unexplained coolant loss fogging windows and a sweet smell inside the car. Sometimes drivers alarmingly notice coolant leaking onto the floor from under the dash.
The heater core is a small radiator that provides heat from the engine to the cabin of the vehicle. This radiator is under the dash on the passenger side of the vehicle. A fan behind the heater core circulates air from the cabin through the radiator to provide heat. If the debris from the engine blocks the passages in the heater core, or it starts to leak, the air does not heat up.
The heater core also provides the hot air the vehicle requires for defrosting the windows. When the core begins to leak, the fan blows moisture from the dripping core toward the windshield. As this hot, moist air contacts the cold windshield, it forms more fog on the glass.
The fluid that leaks from the heater core is corrosive to metal. Without making the required repair, the liquid causes the floor panels to rust, making the issue more serious.
The cost to replace a heater core depends on the vehicle. With some models, replacement is much more complicated than with others. Replacement parts range from $79 to over $500, while labor costs range from $300 to over $1,100, as of March 2015.