My car is a 1991 420SEL (W126), so I'll post this in the S-class area, also. But it's not really a model-specific issue.

My car developed a sudden, but fairly rapid/large coolant leak, from a strange place under the engine.

I got underneath, and discovered that there is a pencil-eraser-sized hole in the engine block, that coolant streams out of. I guess this is a case of corrosion, as the block is aluminum.

I'm looking for any and all ideas as to ways to plug/fix the hole, short of replacing the engine.....

Given that this is exposed to coolant, the "plug" would need to survive exposure to coolant, and temperatures in the 200F range, I suppose. As well as be strong enough to resist the pressure from the pressurized cooling system.

The hole is not really round. It's basically a quarter inch by a third of an inch, and somewhat irregular shape.

It's somewhat accessible from underneath, depending on what the repair procedure would be.

Do shops do things like braise or solder metal in this kind of situation? Is it like radiator repair (albeit aluminum)?

Other thoughts that have crossed my mind (not necessarily GOOD ideas, though!) are:

- some sort of "liquid metal" product, gooped in the hole area and let dry/cure.

- a rubber plug of some kind. It would have to be "squishy" enough to fit into an irregular hole, although perhaps I could drill out the hole area to be more round. I even thought of the basic concept of a tire patch kit - with the rubbeerized patch soaked in some form of glue, then poked though the hole, and partly pulled out again. But I don't know if 1) it would hold, or 2) would it survice exposure to hot coolant.

- if I drill out the hold to be more round, perhaps I could screw a metal screw into the hole, to be the plug.

The car is probably only worth $2000 or so, but it seems a shame to have to part it out, or scrap it, just for this....

 

When I first got my 97 E 320, it developed a leak at the left rear of the motor if you ate at the front of the cat. It was what is called a fteeze plug. These are placed in varios places so if the coolant freezes it will push the plugs out and not crack the block. I doubt that there is a hole in the block it self. My plug was actually a coilant drain
plug which was threaded and was simple to replace with a rachet and socket. However the rest of the plugs are forced in (pressed) and acess may require removal of parts toget to them. See if where the leak is at and look to see if the leak is possibly coming from a metal plug pressed into the block. If the plug it is leaking from looks like it has a place made into it to use a wrench to remove it

 

I don't believe it's from a freeze plug location - the hole is irregular shaped with rough/wavy edges. It's small, maybe 1/4" by 1/3". I probably could drill/ream it out a bit to make the hole more round, and then use some sort of plug to mostly fill the hole. But it is also in some sort of indented area.

I've seen some people claim success with using J-B Weld, although the general consensus is that the RIGHT way to do it would be to have a skilled welder braze in metal to fill the hole - there are brazing rods that are intended for use with aluminum. Still, a number of folks think that J-B Weld will probably work fine, if I can get the area clean and free from grease (using alcohol and possibly a bit of brake cleaner to de-grease the area).

The other suggestion is to drill out the hole slightly, "fill it" with a self-tapping screw of some appropriate size, perhaps also using J-B Weld as a seal around the screw threads.

I figure I have little to lose - a fallback plan to take it to a skilled welder can be done later, if simpler methods don't work, or hold.

 

Good luck.