If the OP wants to do a temporary fix this is what I would do if it were my car.

1) Drain all coolant.
2) Clean the area well and remove all rust, blow dry.
3) Find a similar freeze plug hole elsewhere with easy access and make a wood plug which fits snug-ishly inside the hole.
4) Coat plug with JB weld and plug the culprit hole.
5) Hope for the best.
6) Fill with water to test, if OK replace coolant.

This fix is easy to undo to make a permanent fix later if necessary. Doing a permanent fix is always the best if you can remove the old plug easily. Press the new one in. If access is tight then sand down the new plug and glue with JB weld. Good luck.

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Not MBZ nor A/C trained professional but a die-hard DIY and green engineer. Use the info at your own peril. Picked up 2 Infractions because of disagreements. NOW reversed.

W124 Keyless remote, PM for details. http://www.peachparts.com/shopforum/mercedes-used-parts-sale-wanted/334620-fs-w124-chasis-keyless-remote-%2450-shipped.html

1 X 2006 CDI
1 x 87 300SDL
1 x 87 300D
1 x 87 300TDT wagon
1 x 83 300D
1 x 84 190D ( 5 sp ) - All R134 converted + keyless entry.

I would be affraid, that if it is leaking....That it will soon just pop out....I wouldn't attempt a temp fix, because I don't think any fix will keep it from just popping out....I would hate to have it pop out on the middle of the freeway, over heat the engine and thus making a door stop out of the engine....

It looks like it is behind the oil filter housing....The repair can be done with the engine in the car, timing consuming....yes....can snowball into other repairs....yes....finding the correct plug n tool....will be the hardest part...

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i just took it to my mechanic, i had other things that needed to be done as well anyway. he cringed when i told him about it but said he could take care of it.

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1981 NA 300D 310k miles

LOL, it IS in a bad location given it also needs to be clean when something is installed...nice to have a mechanic you trust....
Cringing is an indicator of a %20 surcharge.

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1980 240d ,

chain elongation, cam marks reference:
http://www.peachparts.com/shopforum/showthread.php?threadid=10414

http://www.peachparts.com/shopforum/diesel-discussion/305365-9-degrees-chain-stretch.html

evap fin cleaning:

http://www.peachparts.com/shopforum/showthread.php?t=156207&highlight=evaporator

A/C thread

http://www.peachparts.com/shopforum/diesel-discussion/297462-c-recommendations-mb-vehicles.html

he's been working on mb diesels for 30 years and usually undercharges by about 20-25% so if i have to eat it on this one thats fine

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1981 NA 300D 310k miles

This part screws out ,it as one o ring on the rear .Put there for the heating unit for pre heating the engine They do get mistaken for welsh plug ar core plug

I am skeptical .
What kind of tool would allow you to unscrew it ?
Looks like a knock in core plug to me.
There is a block drain which can be used to connect the external block heater... but it has a six sided plug clearly meant to be removable by socket.
It is located below the line of core plugs and forward of the one shown.

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1980 240d ,

chain elongation, cam marks reference:
http://www.peachparts.com/shopforum/showthread.php?threadid=10414

http://www.peachparts.com/shopforum/diesel-discussion/305365-9-degrees-chain-stretch.html

evap fin cleaning:

http://www.peachparts.com/shopforum/showthread.php?t=156207&highlight=evaporator

A/C thread

http://www.peachparts.com/shopforum/diesel-discussion/297462-c-recommendations-mb-vehicles.html

As noted, be careful with Bars Leak. It works quite well. I used it in my 70's era cars when in High School in the 80's.

I would not use it in newer cars, as it does have a tendency to plug up heater cores and item with small passage ways.

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RRGrassi


70's Southern Pacific #5608 Fairmont A-4 MOW car

13 VW JSW 2.0 TDI 193K, Tuned with DPF and EGR Delete.

91 W124 300D Turbo replaced, Pressure W/G actuator installed. 210K

90 Dodge D250 5.9 Cummins/5 speed. 400K