After much research, and buoyed by my second success at removal of The Defiant Coolant Plug, I am attempting to record how I THINK it works; what worked for me; and what didn't work.

I hope someone else will find it useful.

Also, I'm attempting a third removal next week. The first two were with the engine out; but in the process, I've developed a method and tooling that I believe can work reasonably well, and safely, with the engine still in place.

At the end of the effort, and since I may never have to perform this task again, I am planning to loan out the tools that I built to make the task easier.

My first attempt was on a 616; removed from the car with around 240K. It spent much of its life in the northeast, where the salt baths gave it some "extra bite", I think.

I was successful in removing that plug, first building a tool for turning the 19mm hex:




This tool is made from an old 13/16" spark plug socket that happened to have a slightly undersized 3/4" hex on its nose, for wrenching. Since it fit in the hex of the coolant plug snugly, I decided to weld it to a 1/2" drive x 13mm impact socket. I selected this socket because its one I never use, as I also have a 3/8" air hammer. It had a nice OD taper on the nose which I inserted into the 13/16" hex, allowing it to be easily tacked dead straight.

It will become clear that the obsession with tool straightness was necessary.
I expected to put some bending load on my home-brewed "Allen" bit. I had no idea how important that criteria would become.

My "zero point" was with this tool powered by a brand new 850 ft-lb air hammer, running at around 600 ft-lb "rated load" -- for 1/2 an hour.

NO LOVE. Didn't budge. I was disappointed, but decided that I really wanted factory pre-heating; as well, I had already purchased the OEM 400W heater, which is a beautiful piece of solid brass -- if you've never seen one. Cheap at $87.

My "first trial" on the 616 used a 3/4" "slider" style breaker bar which is 24" long adapted down to the 1/2" socket drive. This is by plan: IF I snap something along the way, I'd like it to be the adapter, which is the least expensive part. Using a 3/4" socket would have added 2-1/2X the torque capacity at that connection, which would have broken my home-brewed tool, first. At least, that was my thinking at the time.

The 3/4" breaker bar fits neatly inside a piece of schedule 80 hydraulic service tubing, which is 1-1/4" OD and 1/4" wall thick. I use a 2' long chunk of this tube to extend the breaker.

So, first trial, with a 3-1/2' long breaker bar: NO LOVE. Plug didn't budge.

I decided to heat it, with this thinking:

A long time ago, I worked as a "production engineer" at Warner & Swasey, a machine tool company. As part of our regular practice, we seasoned cast iron beds in the "outback" of the factory, in Cleveland, OH -- for up to two years, and as little as 6 months when machine orders were cooking.

As a result, I've seen a few "workarounds" for cast iron on steel rusting problems. We also did refurbishments.

One of the "tricks" I learned was to heat a plug as hard as practical, and then remove it "hot". The thinking was, and is: the plug heats up, and transfers heat to the body of the receiver -- in this case the engine block. Since the receiver is cast iron, the heat migrates away from the hole pretty quickly, but the plug actually FORCES the hole to expand.

When you remove the heat, the cast iron "quenches" the plug in a big hurry, soaking the heat up. The hole "releases" from the plug as it shrinks. This condition persists for a short period, until the hole starts to shrink back in on the plug, and he plug decelerates its cooling rate.

The question for MB blocks is: how hot is "hot enough" to get this release?

I finally got the first plug out with a 6' long "extender" tube on my 3-1/2' bar, for a total torque arm of around 7'. Against this arm, i applied my 180# in a sort of "hammer" mode -- jumping off the ground. and pushing down on the bar.

I also clamped a propane torch to the block and left it running for about 1/2 hour.




S-L-O-O-O-W-L-Y the plug started to back out, finally yielding!

Needless to say, using a 7' long bar while the block is in the car is more than a bit cumbersome. But, the process gave me hope that I could find a design of tool that would work for installing one of the finest block heaters ever offered on this planet!

ON to "trial #2", where I break, and improve the design of the "home brewed" coolant plug remover. And figure out how to remove it with a "regular" length breaker bar!

--frankb