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Bad heater core?

34K views 133 replies 14 participants last post by  Clarkz71 
#1 ·
Just replaced Mono valve for hot air issue problem ,but now leaking coolant at drains below heater core location,I can see the drips when I crawl under there,weird how it just started last week leaking while I was testing old MV for voltage and cleaning the inside of it,guess I'm committed to pull the dash now, what fun.:frown I have a feeling this w124 my son bought on eBay is haunted!
 

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#3 ·
No smell yet,pretty sure its heater core,low coolant light on,top off coolant tank ,drive after 5 min,light back on and fluid dripping out of the drains,I have to pull the dash anyways for pod replacement for flaps,will test heater core,I just started the job, I have theses cut brown ground wires ,think stereo installer did this work,PO was a woman and original owner,doubt she did this hack job.

Any one know what they went to????
 

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#4 ·
No Odors, No Wet Flooring

I'd be looking at hoses, not the heater core. Don't heater cores leak INSIDE the cabin? I think there is a pesky heater hose or two toward the back of that engine, and a valve, maybe? I recall reading about those while researching the forum threads.
That quick loss of coolant also leads me to a hose issue. Did you try leaving the cap off the expansion tank to relieve the pressure in the system? See if that leaks stops without pressure. Don't drive around for a long time without pressure, but if you can warm the engine to operating temps without the leak, then you can tighten the cap, allow it to build pressure and then look for that leak under drier conditions. That much coolant leaking should be easy to see, IMO.

Could you have dislodged a hose, bent it(cracked?) or left off a clamp? Those old formed rubber hoses become brittle as they age. The drains are used to drain liquids from the engine side of the firewall or the cabin side?

Those wires look like something you would see on alarms or remote starters? I bet FloobyDust could tell ya about those. PM him.
 
#5 ·
Based purely on his photo, the leak is coming out two sides, so unless its leaking from different sides of the engine bay, its at least going down into the heater box.

And you are positive it is coolant and not water from condensation at the evaporator?
 
#6 · (Edited)
Did not confirm coolant, but what else, I've seen the stains 3 times in 2 weeks,basically been testing the car and not driving it to work, as far as the heater hose's they stop at firewall and have inspected those,I replaced them 3 years ago, the leak is at A/C Evaporator Drains,I'm just glad its not on the carpet inside,has to be heater core,lots of fluid.
 

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#8 ·
Woohoo! its off! for those attempting this,the 2 top air vents have a rubber boot securing it to the system,those after 20+ years were on there good, use a screwdriver to break the seal ,then it comes off,also I did not remove steering wheel to get dash off.
Now it looks like Cthulhu under there.
 

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#13 ·
This looks terrifying! Is it actually terrible to do or is it an "easier than it looks" scenario?
Having the entire sub frame with the rack and pinion pulled out of my 03 Jetta and sitting on the floor looked crazy, but was really not that difficult of a job. Just wondering if this is similar.
 
#11 ·
Only have a little time each day to work on this project,life gets in the way,have other cars to drive and in no hurry, 1st time doing this project,not hard ,the car comes apart easily just time consuming if you never have done it before!
Now I want to start the car and test the system, still figuring out all those pods,when I tested the center lower pod #40 with vac gauge it was good and flap opened up perfectly to let a/c thru center vent? never have seen that flap open before with dash on? so I want to test the Y7 distribution block outputs ,testing everything in this system before I start throwing parts at it.
have heater core and climate control issues here to fix.
 

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#12 · (Edited)

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#17 ·
From what I understand that whole box doesn't have to come out to replace heater core,that would involve draining precious R12 freon from a/c system.

Yeah, OK.

Let us know how that goes.
 
#14 ·
Not horrible but the thought of doing it is!lol, I'm just lucky I was driving the car instead of my son,he wouldn't have noticed the issue right away,this could have easily filled the carpeting with coolant and ruined the interior.
when he bought the car it had blown head gasket (repaired)with lots of oil in cooling system,I flushed the cooling system really good with some kind of citric stuff? but I don't think the heater matrix got flushed ,3 years ago,I'm wondering if some of the oil deposits in there contributed to failure? whatever,It will work like new soon!
 
#15 ·
Still at it for a hour before work today ,fiddly work for sure ! got one side of heater box off ,and looking inside front looks nice and clean,few bugs inside,drain location has oily residue like coolant, still need to drain coolant and disconnect lines to core,then blow all the coolant out of it, I found this red hazard switch where it sits in picture,how the heck did it get there? it was under plastic vent I removed,bet the guy installing it dropped it while the car was getting built way back when! it looks brand new, also lots of broken glass found under drivers carpeting on floor boards??? hows that happen? a few parts in the back seat and the trunk has more! fun uh? for your viewing pleasure!
 

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#16 ·
I found this red hazard switch where it sits in picture,how the heck did it get there? it was under plastic vent I removed,bet the guy installing it dropped it while the car was getting built way back when! it looks brand new,
You got a brand new switch for FREE from Mercedes! You are the only person ever to get something without charge for your old MB. :devil:grin You could sell it on ebay to offset some of the costs you're incurring for this job. :)
 
#20 ·
Next you will need to remove the dash, please see our Pelican Parts Technical Article on Removing Your Dashboard for more information.


To replace the heater core
you will need to remove the heater box from the car.




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#21 ·
Dash is off,about 1/2 thru removing heater box,not fun but its got to be done,guess it will be easier to remove those rear pods with the box out,only part that that bugs me is losing the R12 I put into it last year,will convert over now,I bought the receiver dryer retrofit kit 2 years ago from Autohauz,had a feeling this would happen! really is big job,but at least I can sit while working on it right! still a drag. 1st time doing this job,any advice along the way will be greatly appreciated!:givemebeer:
 
#28 · (Edited)
Have everything drained and disconnected,ready to pull it out tomorrow,
does the blower unit come out with the whole HVAC box? just wondering.
The blower housing is part of the HVAC case, so YES, it WILL come out with it.


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