How to Repair a Car Heater Core Leaking Antifreeze

What You'll Need
Phillips screwdrivers
Adjustable open-ended wrench
5/16s ratchet
Steering wheel pulling tool

A car heater core that leaks antifreeze can be repaired if you have the proper knowledge. It is not an easy job, but you can do it by taking the following steps:

1. Locating the Leak

Passenger compartment leaks manifest themselves as puddles of green liquid in the front footwells. The puddles can mask a simple hose or a major core element leaks. A trickle of fluid indicates a leaking hose. The core is probably fine. If, on the other hand, there is a large amount of fluid that leaks heavily, it is likely the core. Please note that the external hoses, usually the most visible entering the cab, can also leak. You will find small green puddles near the firewall as an indication.

2. Accessing the Heater Core Element or Hose by Removing the Dash Panel

To remove the dash panel you must remove three screws that are located at the base of the windshield, plus four more, located at either side of the panel must also be removed. They are usually covered by flat plastic trim pieces. Removing the dash will also require removing the glove box. You may also have to pull the steering wheel to complete this and this requires a special tool.

3. Finding the Exact Cause

After the dash panel is removed, you will see the cause of the problem. Hose leaks are very apparent as you will see a worn hose or hose and clamp assembly. Core leaks are feature heavier flows and usually leave the core surrounded by green coolant.

4. Removing the Coolant

Once you have located the problem, you can begin resolve it by removing the anti-freeze/coolant. To remove the antifreeze/coolant, find the outlet at the bottom of the radiator core. There are two types: a butterfly-type stopcock that turns to the left to increase flow, or a 10mm to 15mm nut that you remove with an adjustable wrench. Be sure to place a bucket or large pan below the outlet to catch the coolant and to prevent it from spilling on the ground where it can be hazardous to household pets. Coolant, for example, tastes sweet to cats but is also fatal because it is ethylene glycol.

5. Resolving the Problem

Once you have drained the coolant, remove the hoses, clamps, and heater core so you can dry the system thoroughly with rags. Please dispose of the rags properly. Rather than replace parts piecemeal, obtain new hoses, clamps and a new heater core. Place the new O-ring clamps around the new heater core hoses and tighten them with a 5/16s wrench. Next, place the core in place and tighten down the screws (two to four). You will likely find you can use the 3/8s wrench or flat-bladed screwdriver to complete the job. Be sure to replace all external hoses and clamps as well. At this point, replace the anti-freeze/coolant to ensure that there are no further leaks.

6. Replacing the Dash Panel

Ease the dash panel back into place with as little pressure as possible. It is plastic and can easily break. As a precaution, be sure to work all controls to ensure that the heater and all director or flapper doors work correctly. Hand-tighten the center screw at the windshield and gently push the panel back into place. Replace one screw on each side and hand-tighten it and then replace the second screw. Finish the job by gently tightening all screws and replacing the trim caps.