Visions of a dashectomy were dancing through my head as I noticed a leak at the metal tube which enters the firewall on the driver's side of the car. I can't tell if the leak is coming from the hose or from somewhere behind the firewall out into the engine compartment. The hose looks o.k. and is as tight as can be. Is there another connection behind the dash leading to the heater core that I can check?
There is coolant under the driver's floor mat. I've owned this car for 9 months and always thought there was a leak in the windshield seal. The car started to run hot just recently. I changed the thermostat, but I'm still not down to 180f which is where it used to run at. From my previous experience with these kinds of leaks, it seems that even if you're not losing much coolant, air can get into your system and disrupt the flow of coolant. Please don't tell me I need to take the dash out. Thanks

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'81 300SD

Looks like the Hose hooks right up to the Heater Core Tubing.

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84 300D, 82 Volvo 244Gl Diesel

Thanks for the diagram. I doubt that the aluminum tube has sprung a leak, so I'll pick up a wider hose clamp tomorrow and replace the one on there now which is considerably thinner than the one on my last 240D.

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'81 300SD

Aluminum can corrode through also or even crack.

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84 300D, 82 Volvo 244Gl Diesel

OK, I won't tell you but sounds like classic symptoms of a bad heater core.

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Charles
1983 300D, bought new, 215k+ miles, donated to Purple Hearts veterans charity but I have parts for sale: http://www.peachparts.com/shopforum/showthread.php?t=296386

The good news is that after replacing the hose clamp at the heater core inlet, the car is holding temp between 178f and 188f. The bad news is that coolant is still collecting under my floor mat. Since I can't smell the coolant, I'm not going to worry about it too much for now. After doing a search, I've found that guys have been running Barr's stop leak through their heater cores with an auxillary pump and having some success. Have any of you tried that? I was thinking of using one of those pumps that you put on the end of a cordless drill. Thanks

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'81 300SD

Never worked for me in other cars but, if you don't have an auxiliary pump or monovalve in a 240 (can't remember, but don't think mine did) it may work, though alumiseal may be better. But I'd worry about clogging other things if you have these, the little tubes running around the firewall, or heated washer fluid. Hence, never tried it in a Mercedes.

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1992 300D 305+K miles
1978 240D Sold

Good news and bad news.
Good: Replacing the hose at the heater core inlet got rid of all the coolant leaking down the firewall and finding it's way to the floor mat.
Bad: There is a second leak, and it must be coming from the heater core because there is no moisture along either side of the firewall. It's a very small leak, but since my temperature is fluctuating between 178f and 188f, I'm assuming that pressure is being lost at that leak.
I tried the bar's stop leak procedure running it just through the heater core for 20 minutes. I then reconnected the cooling system and drove the car for 1/2 hour. I saw Winmutt had a post where he was successful with this method but unfortunately I was not. There is still a little water under the floor mat.
I'll start a new thread on the dashectomy if it comes to that. I can live with a small leak as long as I'm not running hotter than 190f. I'm a little more concerned about toxic vapors from the Zerex G-05.

Does anyone have experience with non toxic coolants like Sierra?

Is there a low pressure radiator cap that I can use to take stress off of the heater core? Since I'm in Northern California, I don't deal with extreme temperatures so I think I could get away with the low pressure cap and non toxic coolant if I had to. Thanks

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'81 300SD

Try running the car for a while without pressure in the cooling system. When you put the radiator cap on, only turn it past the notch, dont screw it down. Doing that may give your leak fix a chance to seal it better.

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Grumpy Old Diesel Owners Club group

I no longer question authority, I annoy authority. More effect, less effort....

1967 230-6 auto parts car. rust bucket.
1980 300D now parts car 800k miles
1984 300D 500k miles
1987 250td 160k miles English import
2001 jeep turbo diesel 130k miles
1998 jeep tdi ~ followed me home. Needs a turbo.
1968 Ford F750 truck. 6-354 diesel conversion.
Other toys ~J.D.,Cat & GM ~ mainly earth moving