Welcome all, this is my 1st post. 2 months ago, my daughters 2002 (W203) C240 Sedan, leaked coolant into the passenger side compartment. I performed an emergency bypass....funny, yes. As she needed to depart quickly, and there was an auto parts store near where she broke down, i thought i was being clever. I purchased a 6' long high pressure water hose, and connectors.
I interrupted the coolant flow, below the coolant overflow tank. I saw that the hose, under the resevior, went along the passenger side of the engine, under the windshield. I assumed this was the "Inflow" hose to the heater core. I then Identified the ?Outflow" "return hose" to the backside of the engine. I cut the line there, yes coolant flowed from that line. I then interposed the new water hose at both junctions. With the car on, I could feel the coolant flowing through the line.
My problem is this, and it has taken weeks to identify the location, and at least a couple dozen bottles of coolant, to identify a constant leak? During normal driving, or if i let the car idle long enough, i was finally able to see that coolant was leaking from the line I cut, that goes through the ?firewall/enginewall - into the engine? I plugged the end as it came through the wall. And is leaking from behind the wall, that blind hose. It appears to be below the wiper motor? I did successfully plug the open end of the line i cut. My question is, is there a separate tributary, another coolant line that is feeding coolant to the hose on the back side of the engine, behind the engine wall? I can see a line on the drivers side of the engine, coming off the radiator, and appears to feed towards that direction, but i'm not sure of its purpose (actually i see 3 metal lines, that turn into rubber hoses). .
I'm not a mechanic, just a "Joe" dad trying his best. Chiltons, Haynes, online drawings, either do not show another line, or i just have no idea how to read them.
The car runs like normal, as long as we keep up with the coolant, the temperature does not fluctuate. There is no weird color smoke from the exhaust, and oil color and quantity are normal... HELP.....

I know that on my W126 560SEL, there was a heat exchanger that was located under the windshield in the area where the wipers parked. This was fed by a coolant line that "y"ed from the return line from the heater core (after the monovalve). The presumed purpose was to keep the wipers from freezing to the glass.

Repair would no doubt require removal of the windshield.

Jim

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