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.

I'm adding some here for those who might have more questions. Just adding a few things that might help others with their heater core replacement.

REMOVING THE SCREWS TO THE FRONT OF THE HEATER CORE.

You can either remove the temp controls to get to the upper PITA screws or use a flexible screw driver. Magnetic tip will keep your anger in check too if you drop a screw. I went from under the temp controls to get to the upper screws and had the radio taken out.

REMOVING THE HEATER CORE. PLACING THE NEW ONE IN.

The only real issue with getting that damned thing out of there is the upper left lip where the tubes go into the core. There's a lip that goes around the core at tat area that you have to bend out of the way. Tying the tubes back so you know they aren't in the way. Then I used a small thin pry bar with a 90* bend on one side. Pushed that end over the top of the core and used another pry bar to bend the right side of the plastic out of the way of that upper section that is holding the core in. Came out pretty easily once I did this. Keep in mind you're prying against plastic so take it easy.

You're going to have to bend that same plastic out of the way to get the new core in as well.

O RINGS.

You need 4 smaller ones and 2 larger ones. 2 small ones and 1 larger one for each side of the tubes. Once you have the core out replace the O rings on the heater core side with a small piece of hard plastic to remove the old ones. The O rings tend to mend a bit to the tubes and using anything steel for this is asking for more leaks.

I also replaced the O rings on the engine side of the heater core tubes as well.

BOLTING UP THE TUBES TO THE NEW CORE.

It's very important you get these tubes lined up with the new core before trying to bolt them down. You wont be able to see the end of the tubes and if they are lined up correctly or not with their respective holes. So what I did was the following. Take each tube and push them into place. You can feel them move into place. Then get your flashlight and push the plate that bolts them down as far back as you can. If you can't see the mounting holes and the threaded insert (on the heater core itself) directly behind them, one of the tubes isn't lined up correctly. The plate should also look even and not pushed out on one side more than the other. If you can see the threaded insert just on the other side of the holes you're in good shape. Just make sure you tighten them in increments so you don't chance pinching any of the O rings.

My car is an early model but this may help others needing to do this PITA job. Good luck.

(kopiert aus BF)