Replace a Leaking Car Heater Core

car heater core (rectangular part with ridges)

A car heater core is the unit that produces the heat used in the vehicle's interior heating system. It works in conjunction with the engine's cooling system. The cooling system in a car consists of a network of pipes and tubes that go through the engine and to a radiator in the front of the car. Anti-freeze is pumped through these tubes to carry heat away from the engine.

To do this, the anti-freeze is depressurized while it is in the engine so that it will absorb heat, then pressurized while it is in the radiator so that it will give off heat. The radiator is located in the front of the car so that air can blow across it, thereby allowing it to radiate heat more quickly.

When the driver turns on the heating system, some of the anti-freeze that would go to the radiator is diverted to a to the heater core, which is like a miniature radiator located behind the dashboard of a car. Instead of air being blown across it because of the motion of the car, a small fan is located behind the heater core to blow air past it and through a grate to the vehicle's interior.

If a small hole appears in the heater core, it can leak anti-freeze, which will find its way onto the floor of the front passenger seat. The following set of step by step instructions will give you all the information you need to replace a leaking heater core in your car.

Step 1 - Use Radiator Stop-Leak Additives

If the hole in the heater core is very tiny, it can be fixed using a radiator stop-leak additive, such as BARS Leak Stop. Add a can of one of these products to your radiator fluid.

Step 2 - Test the Stop-Leak Product

To see whether the stop-leak additive worked, run your engine for a few minutes to make sure the fluid is well distributed throughout the cooling system. Check behind the air conditioning grate to see if the heater core is still leaking. If the leak has stopped, you're done.

Step 3 - Bypass Heater Core

If the stop-leak additive didn't work, you will have to bypass the heater core. There are two rubber hoses that attach to the heater core, one for anti-freeze to go in and one for it to go out. If these hoses have clamps, you can disconnect them from the heater core and use a plastic hose connector or hose coupler to attach them together.

You can buy hose connectors and hose couplers in any hose repair kit at an auto supply store or department store. If you cannot access the hose clamps, you will have to cut the rubber hoses and then attach them. Make sure to cut them close enough to the heater core that you still have enough hose to work with.

A leaking heater core will eventually cause a big mess because it will continually leak anti-freeze onto the floor of your car. If you notice a heater core leak, you should get it fixed as soon as possible.