My 1982 300SD has a leak from the heater core area... - PeachParts Mercedes-Benz Forum

vstech · #1 02-02-2015, 12:52 AM

I gave the car away to my helper that assisted me cleaning out the cars from my yard.
It's been great for two years for him, but he started loosing coolant...

I helped him bypass until time to identify the problem got free... Replaced one leaking hose after another, and still the leaks persisted. Pumped the now leak free engine bay cooling system up, only to hear water sprinkling around under the windshield... And trickling out from under the car... Pretty sure sign that the heater core is gone.

Is this as big a nightmare to fix as it looks to me? Will it be easier to swap the drive train into a working body?

Skid Row Joe · #2 02-02-2015, 01:06 AM

Never know until you start to dismantle the under dash area, and find the source of the leak. Might make for a nice tutorial for DD if you do.

;

SD Blue · #3 02-02-2015, 10:59 AM

Are you sure it is the heater core and not the heat exchanger for the windshield in the wiper area?

leathermang · #4 02-02-2015, 11:23 AM

Isn't the heater core replacement listed at like 17 hours of labor in the flat rate manual ?
A student in Florida many years ago did this twice I think... with lots of pictures taken along the way....somewhere in the archives....
Do you have a ' working body' available ?

DieselPaul · #5 02-02-2015, 11:42 AM

Frankly swapping chassis' over a heater core is a little absurd unless the car is a total POS to begin with.

I've done multiple heater cores and evaporators, and its not hard. The 124 one bills at like 20 hours or something. My first go was around 7.5 hours in and out.

You're a proficient technician, just replace the heater core. Its not that big of a deal. I gather you've parted out lots of cars, if you've ever pulled a parts car dash you're already way ahead of the curve in terms of getting it apart efficiently.

My best advice is if you're doing it inside (I.e. Not out in the rain) open the sunroof. The extra light goes a long way. On a 124 I don't pull the seats as some suggest, just slide them all the way back.

eatont9999 · #6 02-02-2015, 12:07 PM

It's not that bad. It is a PITA, though. I can pull a W126 dash in about 2 hours taking my time. Maybe a little more time to reinstall it. Once the dash is out, that is most of the battle. Next is removing the climate box. Never buckets of fun but not worth scrapping a good body and interior over a heater core.

I have coolant leaking from near the brake support on my second 300SD. I can't locate the leak from the top side, so I am possibly looking at the same job soon. Maybe I will get lucky and find it is the windshield heater. At least that can be disabled. Even replacing the windshield is easier than a heater core.

steeleygreg · #7 02-02-2015, 12:40 PM

If I remember correctly the monvalve on my 85 300SD has a port with a hose going into the windshield area. This feeds and heats the windshield from ice. Mine is blocked off currently. The hose connects to a nipple at the bottom of the windshield, I do believe. Not sure how the 82's where setup.

vstech · #8 02-02-2015, 12:58 PM

82 is the same way. I will pinch it off and see if that is the culprit.

bolzano · #9 02-02-2015, 11:32 PM

My leak was a slow one from windshield heater under the right windshield wiper. Dripped on the passenger side of car, USA model 1985 300SD. Used a home made pressure tester. Simply made one by cutting a tire valve off a broken bike inner tube. Fitted it to a small hose with a worm drive clamp. Put hose on a small fitting on radiator from coolant expansion tank. Plugged hole in coolant expansion tank with short hose with plug in it. Used bike pump to pressurize cooling system. Not too much pressure. Maybe coolant tank cap would limit pressure. Saw leak. Confirmed leak from windshield heater visually. Bypassed windshield heat. That leak gone.

eatont9999 · #10 02-16-2015, 01:18 PM

Any update, vstech?

eatont9999 · #11 03-15-2015, 10:25 AM

Update:

I found the leak in my 83 300SD that was dripping coolant out of the windshield drain. Luckily, it is not the windshield heater but the thermo-valve that controls the flow through the heater. It is a $65 part that can be replaced easily if you remove the cowl screen.

Pelican Parts - European Automotive Parts and Accessories - Porsche • BMW • Mercedes • Volkswagen • Audi • Saab • Volvo • MINI

The symptoms of this part failing are as follows:

Intermittent loss of coolant
Overheating when enough coolant has been lost
Inability to maintain coolant system pressure
Gurgling in the heater core area due to coolant loss and air intrusion
Intermittent cabin heat due to no pressure in the system and low coolant

Testing procedures:

Bring vehicle up to temperature with a topped off coolant system
Turn on cabin heat (this is to rule out a heater core issue, the windshield heater is in bypass to the heater core, so it always has the ability to flow).
Check system pressure
Check for leaks on the ground
Remove windscreen cowl and wipers
Check under windscreen heater for coolant
If no coolant under windscreen heater, inspect thermo valve for leaks

If the system cannot maintain pressure for testing, it may need to be pressurized to locate the source of the leak. In my case, this was as easy to do as disconnecting the reservoir return hose, plugging the reservoir and blowing into the hose. The leak revealed itself by the sound of bubbling coming from the thermo valve.

vstech · #12 03-15-2015, 11:15 AM

Wow this is great news. Thanks. I have not had time to search for the problem yet, but I'll start there, thanks!