Heater Core
A small, radiator-like heat exchanger behind the dashboard that uses hot engine coolant to heat the vehicle's cabin.
The heater core is a small radiator-like heat exchanger located deep behind the vehicle's dashboard, inside the HVAC housing. Its primary function is to provide heat to the passenger cabin using the heat generated by the engine's combustion process.
Hot engine coolant flows from the engine block through heater hoses into the tubes of the heater core. As the coolant circulates, a blower fan blows air across the thin metal fins of the core. The air absorbs heat from the coolant and is directed through the dashboard vents into the cabin. In this way, the heater core acts as an auxiliary radiator, helping cool the engine while heating the cabin.
Heater cores can fail in two main ways: clogging or leaking. A clogged heater core restricts coolant flow, resulting in little or no heat in the cabin. A leaking heater core allows coolant to escape into the passenger footwell, soaking the carpet with sweet-smelling fluid, causing the windows to fog with a greasy film when the defroster is on, and leading to low coolant levels and engine overheating.
Replacing a heater core is a highly labor-intensive repair on most vehicles, often requiring the complete removal of the dashboard, steering column, and HVAC unit, which can take 6 to 10 hours of professional labor.