How to Bypass a Car Heater Core

What You'll Need
Set of wrenches
Wire cutters
Hose connector or hose coupler

A car heater core is the part of the engine's cooling system that heats up the interior of the car when the heat is turned on. The cooling system in a car is made up of hoses and pipes that circulate antifreeze around to different parts of the car. The antifreeze is pumped through the engine — where it absorbs heat — then routed to a radiator at the front of the car.

In the radiator, the antifreeze is pressurized in a long coil of piping so that it will give off heat more quickly, and the motion of the car forces air through the radiator to make the heat dissipate even faster. When the interior heating system is turned on, some of the antifreeze that would be routed to the radiator is sent to the heater core located behind the air conditioning grates on the dashboard. The heater core is like a miniature radiator, and a fan blows air past it and through the grating so that it will heat up before entering the interior of the car. When the heater core develops a hole, it can leak antifreeze, which usually finds its way to the floor of the passenger side and collects there until the hole is fixed. The following set of step-by-step instructions will give you all the information you need to fix a heater core leak by bypassing the heater core.

Step 1 - Remove Air Conditioning Grating or Dash Board Cover

A tan car on the road.

In order to get at your heater core, you may need to take off the dashboard cover, but if your air conditioning gratings are in the right place you may be able to get away with only removing the gratings. It depends on which heater core is leaking and whether it is directly behind the grating.

Step 2 - Remove Hoses

There are two hoses that run into the heater core, one for antifreeze to go in and one for it to go back to the engine. If these hoses have clamps, you can easily remove them. Otherwise, you will have to cut them. If you have to cut them, make sure to do it as close to the heater core as possible so as to maximize the remaining length of hose you have to work with. Do not start working with the heater core while it is still hot; wait until the engine has been off for a few hours.

Step 3 - Connect the Hoses Together

A red car.

Use a hose connector or hose coupler to attach the two ends of hose together. That way, the antifreeze that would be routed through the heater core will instead just go through a short loop of tubing. You can buy hose connectors or hose couplers in a hose repair kit at any auto supply store.

Bypassing the heater core disables the interior heating system in your car, so if you have to bypass your heater core, make sure to have it replaced and reattached before winter. This is a relatively complex process, but it costs hundreds of dollars to have a professional do it for you.