Anyone done a W126 heater core?
 

Starting to notice the infamous coolant smell from my vents. No way I'm gonna pay somebody to do this job. Can anyone outline the steps involved? Searched here, but can't find anything. Thanks!!

A good dealer tech can do that job in 10+- hrs.

The dash & heater box must be removed.

You might search for posts on an evaporator change, as they are similar. Also, I remember seeing this job documented with photos:very informative, on either this forum or another Mercedes forum; maybe the MB club's forum.
In any case, I read as much as I could on this because I figured I'd face it one day. You have to remoave the dash, and it sounds daunting. I learned from repairing my sunroof: it's lots worse to dread it and put it off and it wasn't nearly as bad as I expected. Great satisfaction to complete the job also. Just get information, work carefully and methodically, don't get impatient and break things; document with photos as you take it apart, keep fasteners together in some sort of order so you will have an idea where they go. It might be possible for you to look at a W126 in a salvage yard, to get an idea of what's underneath the dash pad, and if there is one near you, you can go look at it for a reference if you get in a bind.
My cousin works on the tough cases at his home shop: older vehicles which people can't afford to take to the dealer shops. He says the worst heater core/evaporator job he has ever seen is the Lincoln Navigator.
If you would like, you can document your job with photos and post here for those of us with this job in our future. And good luck!

It just takes alot of time. Take good pictures for yourself of the actual heater box before you get into it. There are several levers that need to go back properly after you take it apart and pictures help alot.
I did my evaporator and did my heater core just because it was also in the heater box. I would suggest replacing the evaporator while you do the heater core. You really only want to do this one time.

I'm not sure where it is at the moment, but there is a photographic tutorial of a shop doing it that's been linked to a few times here on the forum.

Same as for evaporator.



Remove front seats. I've done it both ways, it's much more accessible with seats out.

Remove console.

Remove dash.

Remove HVAC box.


Installation is reverse of the above.



Helps to have the factory manual.
Search for documentation where someone else has done it.
Make lots of notes how stuff disassembles, and store fasteners in baggies for each component.
You also need to partially disassemble in front of the windshield to access the heater core pipe stubs.

All in all, wasn't too bad, just tedious.