Quote Originally Posted by Kurtanius21 View Post
Why would the heater core itself need to be replaced? Isn't it just a solid piece of metal?
The heater core is basically a small radiator that's mounted inside the "HVAC suitcase" under your dash. Coolant from the engine is circulated through the inside of it, and air from the cabin fan motor is blown through the fins. Heat is exchanged from the coolant to the air, and this is where your cabin heat comes from. There are little trap doors you control with the levers to route the air through to the floor and/or up through the defrost ducts. Since heater cores are basically little radiators, they can spring leaks (just like their big brothers can). When heater cores leak, they can be a real problem because coolant is now leaking inside under your dash. This also increases humidity (a lot) and turns defrosters into "frosters" (steam that smells like antifreeze covers the inside of your windshield when you turn on the defroster). Of course the carpets get wet and stained with coolant too. In short, nothing good comes from a leaky heater core. Tim