I read of others doing this, so tried it last Xmas when the car was back. Pot of water w/ silicate "coolant sealant", circulated w/ a 300D electric water pump. My son uses this 84 300D at college in San Diego, so he doesn't need much heat and a slight leak is tolerable. He won't answer whether the fix worked (ungrateful kid wants a new car). That same week, Car Talk had a call from a lady in Santa Cruz. They said "you don't need a heater, well maybe there, but not if you lived in San Diego". I don't think they even put heaters in the cars sold 20 miles away in Mexico.

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If you're going to try that stuff that's an excellent way to do it!

-J

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1991 350SDL. 230,000 miles (new motor @ 150,000). Blown head gasket

Tesla Model 3. 205,000 miles. Been to 48 states!
Past: A fleet of VW TDIs.... including a V10,a Dieselgate Passat, and 2 ECOdiesels.
2014 Cadillac ELR
2013 Fiat 500E.

A couple years ago a friend had a leaking heater core on a 240D (that I sold him 6 years previous) so we pumped hot "stop leak" through it, and its still fixed Theres no way I want to pull a heater core

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1985 Euro 240D 5 spd 140K
1979 240D 5 spd, 40K on engine rebuild
1994 Dodge/Cummins, 5 spd, 121K
1964 Allice Chalmers D15 tractor
2014 Kubota L3800 tractor
1964 VW bug

"Lifes too short to drive a boring car"

Take it from me, it's not an easy job, but I did it.

I found so many things that were done WRONG on my car by 3 previous owners repair guys. The heater core was replaced around 2002, with the OEM replacement, but they didnt even put the heater box back together right, damaged vacuum lines, and had a sensor wire running across one of the defroster vent openings... I could look down in there thru the windshield and see the wire!

When I did mine, I got everything put back where it is supposed to be. There are no rattles and squeaks anymore, because I replaced ALL of the screws, and the missing ones were aquired at my local Benz junkyard.

Now, the heater, and all door flaps work correctly. No vacuum leaks anymore. Total time on the job: about 9 hours. Every time I run the heater now, I feel good.

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My first Mercedes Benz. 4/6/07.

1984 190E (201 024) 2.3L four.

Nice job. In San Diego an alternative would have been to bypass the heater core and install a small 12 volt heater for the few times heat is needed.

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

I guess the heater core replacing job on a w115 is a real bear. My indy friend said it was something like a 30 or 40 shop hour job .

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1985 Euro 240D 5 spd 140K
1979 240D 5 spd, 40K on engine rebuild
1994 Dodge/Cummins, 5 spd, 121K
1964 Allice Chalmers D15 tractor
2014 Kubota L3800 tractor
1964 VW bug

"Lifes too short to drive a boring car"