RE: 523 heater core replacement (longish)

["John Y. Hung" <jhung@xxxxxxxxxxxxxx>]

Dear Rod,

If you smell coolant (sweet sugary smell to me), there must be a leak.
Test the heater core this way:  Set the controls for low defrost, gently
blowing the hot air onto the windshield.  If there is a heater core leak,
moisture in the warm air will condense on the inside of the windshield in
cold weather.  In other words, the front windshield fogs up.  This may not
work well for very small leaks.  A sure test is to use a cooling system
pressure gauge, but I don't know many folks who have one.  You might be
able to borrow one from a good garage (also hard to find).  You're not
likely to get drips inside the car because the heater box has a water drain
to the outside to remove A/C condensation.  Now for the story of my '86
325e.

On my car, both the control valve AND the heater core failed.  The control
valve wouldn't shut off because of a rotten seal, probably due to age.  So
hot coolant always ran through the heater core, even when the temperature
dial was fully in the blue zone (cool).  Of course, I didn't know how long
the heater core was being "cooked to death" because warm air isn't mixed in
until the temperature dial is turned clockwise into the red zone. The
heater core has a plastic end cap (called a header) that also serves as
part of the heater box wall.  That header can crack over time, especially
if hot coolant is always running through  when it should be shut off.  My
header eventually failed catastrophically, spewing steaming hot coolant all
over the driver's side footwell, distorting an air duct, and soaking the
radio above.  Fortunately, the driver was not injured, but she received
quite a scare!   (Don't feel that BMW is being cheap to use plastic
headers, because practically everyone does it, radiators included.  Hey,
the car is over 14 years old!)

The Bentley manual has good instructions (Chapter 12) for replacing the
valve and heater core (I bought new from BMP Design in Texas.  I think
Bavarian Autosport is another good source).  Small hands are helpful in
replacing the control valve, which is electrically controlled.  The heater
core is not difficult to replace, but the lower left instrument panel trim
and shift console  need to be removed to gain access.  Lots of small screws
and a few small nuts to keep track of.  It helped me to push the driver's
seat all the way back, so that I could get into the driver's side underdash
area.  I soaked the distorted air duct in boiling water to soften it up,
and molded it back into semi-decent shape.  The radio had to be
disconnected for a few days and allowed to dry out.  Afterwards, I had to
enter the security code to restart it.

Let me know if you need detailed instructions - I'll mail them.

Best wishes,

John Hung
Auburn, AL
'86 325e

>Date: Mon, 10 Jan 2000 21:23:54 -0800
>From: "Rod Birch" <HOTROD930@domain.elided>
>Subject: 1986 325 heater core replacement?  do I need one?  Should I shoot
>the car instead?
>
>HI all,
>
>I've recently begun smelling the faint hint of coolant inside my car when
>turning on the heater, even with the fan off, if I open the vent with the
>temperature knob in the "warm zone" I smell it.  I haven't noticed loss of
>coolant, or anything dripping into the interior.  Is this a sign that I need
>to replace my heater core?  What's involved with the heater core
>replacement?  I know that many cars involve 8-12 hours of sheer frustration
>to change them and complete disassembly of the dash (which apparently comes
>out easily if the entire interior is stripped and there's no windshield).
>What am I in for?
>
>any help would be appreciated...
>
>- -Rod
>
>>From the Desk of Rod Birch

------------------------------