M103 freeze plug leaking
 

When I changed the head gasket two years ago on my 300SE I replaced all the freeze plugs, except for the psg rear one with the hex screw and it now starts to leak coolant. Found this at pelican parts, is it the right part for the early m103, would think they are all the same? What's the best way to replace it, I can reach it without taking off the exhaust manifold, but I'm afraid the old plug will break when taking it out because of rust. Any pointers on how to tackle this and keep it simple?

https://www.pelicanparts.com/More_Info/1179970230MBZ.htm?pn=117-997-02-30-MBZ&bt=Y&fs=0&SVSVSI=3353&fbclid=IwAR25SL-qju1fW9Mb4gurnQ4wkBQMDOLc_LLV2GhRuMzkjJdK35ZCu4ToSX8

If it's just seepage try dropping a couple of Bar's Leaks tablets or liquid into the cooling system . A friend of mine who managed the Viper plant before the DB merger said it was SOP to add a couple of tablet to the Viper cooling system at the plant and most automotive plants did the same.

Duke

It's more than seeping unfortunately. The coolant reservoir was empty after a couple of hours of city driving.

Got a new freeze plug from the dealer, unfortunately the correct O-ring needs to come from Germany. :rolleyes: Is there anything specific about this MB-ring, or can I just use a generic one from the shelf?

Wait for the correct O-ring unless you know what material it is made from and can match it.

Good luck!!!

Makes sense with the coolant and heat from the engine. Thanks!

If I was me, any o-ring would do. Put some teflon tape for good measure.

location
 

This is the part and its location .pic to follow .

this one

Yep, that's the one.

Okay, I have a problem. It's leaking in the inside of the plug and for some reason the hex is rounded, can't get a grip with a 22mm socket, it will slip. What to do now?

I've had success epoxying internal hex drivers into rounded fasteners. Did this on a W123 diesel starter bolt and it worked. The epoxy fills the gaps and prevents the hex from slipping.

Good luck!!!

The trick is to use a chisel and start with tight socket on hex and punch it on the outer most lip, use plenty of wd- 40 or other lube eventually loosens it will get distorted , and worse case dremel tool it in half (the plug)with out damaging the block

Thanks for the tips. I have to work a couple of days and will continue Friday again. I report back.