My worst nightmare - possible heater core leak !

[yogiysh]

I've been reading all previous posts regarding heater issues with the w108 and I think I have to face up to my worst nightmare...

I discovered a small coolant leak coming from the heater unit dripping down on the transmission well !

While under the dash and the engine running(at its operating temp) I openned and closed the heater taps and noticed coolant dripping from them.
So as explained in the previous posts I replaced the gaskets after discovering that the heater taps on the Oz models are at a different place from the US models (they're down low near the transmission well rather than up behind the ash tray or radio). All went well and finished the job in less than an hour coz the taps were so acccessible and NO MORE LEAKS . . . from the taps anyway.

It only lasted for a few days and then started again and I checked the heater taps and they're 100% not leaking!

I had the radiator replaced a few months ago and had it pressure tested again and all checked out fine and no cooling issues.

I'm worried that since the pressure is being maintained in the cooling system the problem is actually moving from one place to the next weakest point so to speak.

Can you please advise if there are hoses that connect the heater core to the pipes that come through the firewall? The MB Star Classic CD is no help with diagrams - just as a last possibility for leaks other than the HEATER CORE.

Can you please advise on how best I can tackle this one.

Cheers,

Ysmael


ps - it's coming into summer here and I've thought about bypassing the heater but I'm just avoiding the issue again.

[MunichTaxi]

I replaced my core with a new core for a 1984 Mercury Marquis.
Raidiator Barn.com has the dimensions on the website, so I just matched them up. Cost was $35.00 dollars.

[yogiysh]

Thanks MunichTaxi, I might have to take the replacement option. I just enquired about the price of a recore for the heater core and it comes out to be the same prices as when I did the radiator !! - and that's with me doing the estimated 14hrs (if I new what I was doing) taking it out of the car in the first place.

I'm just working up the courage to start taking out the dash to get to the heater unit as I still don't know if it's the heater core or the connecting hoses.

Cheers,

Ysmael

[nachi11744]

Hello,
I have no experience with heater cores, but would it be possible for you to look into the area of the leak with a mirror and torchlight?
That may help you pinpoint the leak. There may already be someone in there before you that has done some *modification* that could be leaking now.
Just my 0.2 cents

[yogiysh]

Thanks nachi11744, there is no visiblity into the heater box to see the heater core or lines, even through the bottom vents when they're open. I can't believe how well packed everything is under the dash for such a big car - I can now believe they say that MB designed the W108 car around the heater unit !! ... Still a brilliant product of engineering though.

As a last resort prior to pulling everything out, I'm going to remove the windshield wipers and cowl cover, and leaf filters today to see or reach any of the heater lines.

Cheers,

Ysmael

[dmorrison]

A little advise, since I had to replace the evaporator in the 300TD. TAKE DIGITAL PICTURES EVERY STEP OF THE WAY. IF YOU DON'T HAVE A DIGITAL CAMERA ---BUY ONE--. you will be much happier when you realize you forgot how something was assembled and you have the digital pictures.
Use the highest resolution on the camera and save them to a CD. I have them for the W123 dash removal and reasembly, So If anyone needs them or I need it. I have it.

After completely rebuilding a 65 Mustang and doing extensive work on the 82 300TD I realize how important the digital camera is.

Dave

PS be ready to "rebuild some things while your in there". You dont' want to do this again so you might as well do the little things while you have it apart. "while I'm at it itis" is a terrible delayer of car rebuilds.

[yogiysh]

Thank you Dave for this great advice - I will be taking lots of pictures.

Just assessing what else needs to be done but so far not much - the timbers in the dash are pretty good apart from fading.

I've got European Wallnut which faded to a lighter shade but I'm sure I'll come across something along the way.

I'll check the AC evaporator but at this stage the AC doesn't leak and the only issue I need to address with the AC system is the lubrication maintenance.


Cheers,

Ysmael

[Benzcrusher]

I am convinced that MB had child or liliputian labor OR a severly hungover designer when it came to the 108/ 109 dash. That Behr heater unit is a ***** to get at... The clamshell halves are secured by many tiny spring steel clips, remove them all or you will break something.
The 108 heater is as stupid and counter-intutive as that thumb screw which holds the speedo cluster in place!!!

[Arthur Dalton]

Many a 108 has wound up in the scrap yard cuz of a leaky heater core or bad blower motor...
The Straw that breaks the Camels back.....

[yogiysh]

Not to worry, I won't be letting this one go that easily !!!

It was suggested to me also that since cooling system is maintaining the pressure and the leak is minor, to add a small amount of radiator stop leak into the coolant and see if it stops the leak.....hmmm.

I don't know if its worth a try.

[nachi11744]

It was suggested to me also that since cooling system is maintaining the pressure and the leak is minor, to add a small amount of radiator stop leak into the coolant and see if it stops the leak

FWIW, Land Rover V-8s and Range Rovers were filled with a product called BARSLEAKS from the factory to reduce coolant leakage complaints on NEW vehicles.
If you do use a stop leak, pour in only half first and drive with the heater on FULL for a few days to stop the leak. The less of this stuff used, the better.
Just my 2 cents.