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.

Remove Center Console

Disconnect ground side of battery.

Block the car so it will not roll with the tranny in N

and the emergency brake off.

Remove shift knob. Mine was the leather shift knob

with no set screw or clip ring. Check to see if you
have either. My method is to put the key in the
ignition, move shift to D and just pull HARD straight
up off the shaft.
Remove the rear ashtray in the center console (two
plastic screws, with inserts.) Remove the screw found
beneath the ashtray.
To avoid problems, may I suggest putting hardware in
little bags and leaving them with the components
removed?

Remove Multi-
Information Display in the center console. Push up
through the hole in the bottom of the storage tray and
pull out. It doesn’t seem to come out easy, but
eventually the display will come out. I’m still not
sure how I got it out, just wiggled it around. It snaps
on each side.

Remove the tray, unplug the connectors. Disconnect

the Multi-display. Press detent lock down (thumb)
and move lever over the detent to release the
connector.

Carefully ply up the Hazard Warning Switch behind

the shift lever using a small screwdriver.

Carefully pry the connector off of the back of the

switch.

Remove the screw beneath the hazard switch. Leave

the boot around emergency brake handle but unclip it
from console. Pull the rear portion of the center
console back to remove. Snake the emergency brake
boot through the hole and remove the console.
In the front half of the console, remove two screws at
the top front of the console (they are vertical, below the
Heater/AC controller.

Remove the nut at the rear of the front console.

Reach under the black center of the console and pop

up the switch groups. Grip the body of the connector
and wiggle to unplug switches,

- except the middle bottom on left – that one you

have to push the yellow switch out of the way,
then slide the latch of the center switch towards
the yellow switch to release the connector.

Lift (unsnap) the center shift console (with the

“PRN321”) and disconnect the Auto/Manual switch,
then the small connector to the shift LEDs (Caution:
the little circuilt board breaks off easy and the
connector is hard to unplug.)

Insert the key into the ignition, turn to the first detent, set the shift lever to the back (“1”)
to make room and remove the front half of the shift console (Black and tan portions
combined) as one unit.
Remove Glove Box

Remove 8 screws – two at the top inside the vents above the
glove box, two just under the lip of the glove box door
(covered by small covers – pry up with small screw driver),
two above the hinge, and two underneath. The last two have
larger washers, so keep separate.

Remove the vent panel above the glove box door.

Remove the light inside glove box – pry behind the lens at
the rear of the glove box to pop it downward. It and the
built-in switch will fall downwards. Carefully unplug the
connector (use a
small screw
driver to help
release the little
tab in the
middle.)

Remove the bolt (10mm socket needed)

behind the light (if present.)

Unclip the flashlight holder with a small screw driver

on both sides.

The whole glove box should be free to remove.

Remove Drivers Panel below the Steering Wheel

Remove three screws – two black ones left and right at the top, one silver colored at the
lower right that hold the panel below the steering wheel. The whole panel pulls out,
working portions from under the pedals and left front console panel.

Unclip light

Squeeze the sides of each On Board Diagnostics

connector and unplug.

Remove the big padded bolster under the steering

wheel (10 mm socket.)

Remove plastic heater duct above drivers pedals –

held by two plastic pins, one on bottom near heater – pry this one out, or just wiggle the
whole thing and the duct will come out.

Heater Core

Remove the temperature sensors from the heater box

– grip the edges of the connectors and unlatch the
connectors from the two sensors.

Pull out the two temp sensors (they snap into place) –
caution, they are about 4” long.

The cover over the heater core is held by seven

screws. The bottom ones are easy – see picture
at right.

Three of them
are almost impossible to reach, so here is how I did it.
The top two are behind the heater/AC controller. Reach
in behind and push it out. Press the release and unlatch
the large blue connector. Pull straight out on the small
black connector.
 Reach in and remove the two upper screws of the
heater core cover.

The last screw is behind the flat steel brace

running sideways around to the glove box. I
drilled a pilot hole then a larger hole to be able to
reach in and remove the screw. Use something
behind the brace so the drill won’t drill a hole in
the cover – believe me, the drill WILL hurt the
cover. (I used a putty knife.) I also used a paper
towel below to catch debris. Drill the hole a little
higher than I did – just below the plastic panel. If
you don’t have a T-25 torx bit long enough, use a
long 7/64 allen wrench.

Pry the clip off the heater controller harness on the

front of the heater core cover. I used a small screw
driver on the side to release the two sharp teeth that
grip the cover.

I also removed the radio, which allows for some

flexing of the plastic to help removal of the heater
cover. The radio is removed by opening the two
little doors on each side of the face, and using the
special 5-sided allen type wrench – or you may be
able to use a normal allen wrench if you are careful.
You also might consider grinding down a nail or
something to make a 5-sided wrench. The big
connector on the back of the radio is a little
challenging. There are four pins (2 each side) visible through the connector latch slots.
Pry the connector latch up with a large screw driver where shown on the connector.
When the latch is fully extended (see picture) the connector will just fall off the radio.
 It is very difficult to work the cover out from under the
dash. I found a molded cable bracket not being used,
and in the way. I cut it off with a large pair of wire
cutters.

If you pull back one side of the heater core cover you will see there is a vent flap inside
the cover that is in the way. To make it retract, temporarily hook up the battery, insert
the key and turn the ignition on until this flap retracts out of the way (straight up and
down.) Move any wiring harnesses out of the way and carefully move the cover to the
left and out under the steering column. It is not easy, tabs and pieces of it will hang up on
everything, so take your time. It may require a little flexing of the cover also.

Unsnap both ends of the actuating arm (about 4” long,

on the right side of the heater core) that operates the
flap in front of the heater core. I used a screw driver
to force the arm out of the two holes that the tabs go
through.

To remove the shaft that holds the flaps, pry the left
side of the heater core housing to the left enough for
the shaft bearing to come out of the housing. Pull the
shaft away from the core and slide it to the left, taking
the left flap and the shaft out, but leaving the right
flap in place.

Drain the antifreeze. I was successful in just loosening the bleed screw next to the
radiator cap and siphoning the antifreeze back into an empty gallon bottle. This seemed
to have taken enough water out of the system.
 Unbolt the heater pipes from the heater core. This is
not an easy job either (getting used to this now?) On
the left side of the core are three aluminum pipes
going to the core, held by three bolts through a plate.
The bolts go into some metal inserts in the plastic
core header. Only two of these bolts are visible. I
used an 8mm
¼” drive socket; ¼” flex joint swivel and various
extensions and handles to get them out. Remove
the hidden one first, then put rags under the area to
catch any antifreeze and remove the two remaining
bolts.

Carefully pull the three pipes away from the heater

core. I used a screw driver to lift a portion of the
housing next to the pipes to get a peak in to determine if
they are back enough.

Remove Heater Core (yea, right – easier said than done.) Wiggle the core toward you
and up. I used a screw driver to hook over a ridge on the upper left, as well as a screw
drive going into the core where the closest pipe is connected. Be very careful with the
actuator arm from the flap drive motor at the upper right corner of the core – it is a force
fit to get the core past this arm. Lift the core toward you and up until it is clear of the
housing.

Slide the core to the left, holding rags to the inlet tubes – antifreeze WILL spill out as you
tilt it down to get it out.
Replacing the Cabin Filter

While you have the glove box out, you might as well replace the cabin air filter. I found
mine really packed with dirt and bits of leaves (probably had never been changed in
120,000 miles……)

If the panel under the glove box hasn’t been removed,

remove it. You will need to unclip the light from the
top side then pull it back through the hole.

Pull out the air

vent plumbing.
It is a piece of plastic with two arms. Push down on
it in the large round hole in the horizontal sheet
metal brace to the right of the heater.

Reach in behind the heater housing and find the

knob of the cabin air filter cover – it is barely visible. Turn it counter-clock-wise about
90 degrees and remove the cover. It may not unlatch or come out easily, be careful not to
pull too hard as it will break the latch (ask me how I know, though it seems to still work
properly.)

Unbolt the computer bench behind the glove box to

allow room to remove the filter. This is done with an
8mm socket and long extensions. Remove one screw
in the back (see picture left) and two screws in front
which hold the tray to the top frame. Let computer
the tray hang down on its wires.
I might suggest taking a mirror and visually seeing where the filter is located when it is
seated, as it will be hard to tell if the new one is properly seated without some visual aid.

The picture is taken looking somewhat up at the

heater on the left and the computers on the right. The
filter comes out in two pieces with a hinge in the
middle. Reach
in and wiggle
out the filter by
its tab (yuck!)

Reinstalling the Heater Core

Very carefully remove the three O-rings from the

aluminum pipes. Caution: use ridged plastic or some
other non-hard tool to remove the O-rings, otherwise
you may scratch the soft aluminum and you WILL
have another heater core leak!

Apply supplied foam tape to new core, using the old

one as a pattern.

Replace O-rings onto aluminum tubes. (I added a

little not-hardening gasket maker to each O-ring
before installing, just to be sure.)

Carefully work the core back into place, being

careful of the flap actuator arm (upper right corner)
and the foam insulation.

Work each aluminum tube back into place in the heater core so each O-ring is seated and
the plate can be positioned. This is not easy to do, but work at it. When the plate is
close, insert all three screws and then carefully tighten. Bentley says 27 in/lbs, or about 2
ft/lbs (remember, that is 2 pounds of force on a 12” (1 foot) wrench handle.) I tightened
more than that.
To test for leaks

Put antifreeze back into the car (fill to the top of radiator tank with the bleed screw open.)
When no more air comes out of the bleed screw, close it. (On M3 models, the bleed
screw is on thermostat housing.)

Hook up the two cables to the Heater/AC controller.

I also plugged in the window control switches temporarily.

Temporarily hook up the battery.

Start the engine, turn on the heater and set it for high temperature. Check for leaks (you
can actually see antifreeze flowing in the core – there will be a big air bubble in the top
tank.)

Check the bleed screw for air and add antifreeze/water if the tank is too low. Rev the
engine to help push air out of the heater pipes.

Check antifreeze level again, put on the radiator cap, temporarily install the shift knob
and go for a drive until the temperature is up to normal and pressure has built up in the
cooling system. This is the critical test for leaks. Let the car sit until it cools off to make
sure there are no seeps in the system.

Reinstall the flap and shaft that goes in front of the heater core. Pry the left side of the
heater box to install shaft, then install the actuating flap link to the actuator. Test by
turning on the ignition to see if it closes properly.

With the flap closed, carefully work the heater core cover back onto the heater box.

The remainder of the reassembly is the reverse of the dismantling process. Take your
time and it will all work out.

It is soooooo nice not to have foggy windshields and the smell of antifreeze in the car!