What is a heater core?

A heater core works in cooperation with the engine’s cooling system. Now, the cooling system is in charge of removing the heat from the engine. It sends this anti-freeze to the radiator when it will be cooled again be the rushing outside air. When it is cooled, it is sent to the engine. The heater core can be thought of as a mini radiator located inside the dashboard. So the anti-freeze circulates throughout the engine, radiator and heater core.
If you turn on the heater, a door opens in the heater core area. The blower, or also known as the a/c fan, will blow air from the heater core into the dashboard until it reaches the passenger compartment. If you find a leak on your passenger floorboard under the carpet, it means that your heater core leaked anti-freeze. Other signs of leakage are sweet odor in the car and a greasy film on the inside of the windows.
You are probably wondering what causes this. Well, the most common cause is rusting. When you don’t flush your cooling system regularly, rust can build up. Anti-freeze in the cooling system can cause rust to build up. So it is highly recommended that you flush and replace it periodically to make sure your system is working. It can also help you avoid those expensive repairs. If you have rusty anti-freeze, it could mean that you have a coolant leak in your cooling system so air is entering the system. It can be caused by leaky radiator, heater core, water pump or radiator hose. The rust can damage the radiator and other internal engine parts too.
To stop the anti-freeze from leaking on the floorboard, you can just replace the defective heater core, as recommended by most mechanics. In case you want something temporary, you can use a can of radiator stop leak additive and see if it can fix the hole. In more extreme measures, you can just cut off the flow of anti-freeze to the heater core. There are two heater hoses connected to the heater core. You can cut or block these with a hose clamp, or you can insert a small hose splice between them to create a loop so they avoid the heater core. Blocking it is useful in summer time as a temporary repair. But if you have the budget for repairs, it is advised to go to a mechanic.