Heater Core Replacement (also Cabin Filter Replacement) – Late E36
Steps required to remove and replace the heater core from a ’97 BMW 318i sedan, with automatic transmission, basic multi-display and standard radio. Other E36 models will hopefully be very similar, though the earlier rotary-knob heater/AC controller will be substantially different in that area. To replace the cabin air filter located behind the heater box, skip directly to “Remove Glove Box”, then “Cabin Filter.” Symptoms of a heater core leak (as far as I know.) In my case, when you turned on the heater on a cool morning, the windshield would fog up, especially the drivers side. Running the defogger really didn’t help very much. Even if it did not fog up, you could smell the semi-sweet smell of anti-freeze. I never lost very much antifreeze – only added about a gallon of de-ionized water over a period of one year, so obviously the leak was very small. The sign of a major failure I would think would be antifreeze draining out the bottom of the heater, which would cause a puddle under the transmission. Note: Taking this car apart is like solving one mechanical puzzle after another! It has been suggested that at the factory they hold up the heater core and build the car around it. Almost every step required research from Berkley, the forums, or just plain trying to figure it out. Hardware mostly snaps together, even the ones held together with screws. Easy to put together at the factory, but difficult to take apart when you don’t know the secrets. Hopefully this will help you find the secrets and not break anything (like I have.) I wrote 20 pages of notes and took 68 pictures to describe this. I hope I never have to do it again. Expect to take a LOT of time to do this. I spent a week on and off working on it, but the total time was in excess of 20 hours. With this information, I hope you can cut that in half. Follow the steps in the order given, for in a lot of cases, one step will require completion of a previous step.