THE Definitive Block Heater Coolant Plug Removal Thread

[franklynb]

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

[kerry]

This is interesting. I once disassembled about 10 cast iron radiators whose sections where screwed together with threaded nipples that had been in place for nearly 100yrs. My experience with those radiators me develop my own procedure for the block heater--install a lower radiator hose heater.

[charmalu]

I had heard that these plugs were a PITA to remove, and some say the block can crack trying to remove them.

I had my indy put one in a few years ago, I didn`t ask, and he didn`t say how hard it was. I just paid him.

The one I have installed now came with the new engine. The plug came right out. not sure how metric Motors goes about removing them from old engines they rebuild.

this is a nice write up you did,

Charlie

[showme]

Let us know how it goes with the motor in. By that time I'll have the lower hose heater in. (While my block heater sets on my work bench, still in the original container)

[franklynb]

Trial #2: Also Know As "Heat IS Your Best Friend!"

Originally Posted by charmalu

I had heard that these plugs were a PITA to remove, and some say the block can crack trying to remove them.
Charlie

And I believe they might be right!

Having acquired a tired 257K 300D, which I drove from Arizona to Milwaukee after a cursory inspection and a few minor repairs; AND a spare 617.912 engine with 2 degrees of stretch in the chain, but an apparent leaking head gasket:

I decided to chase that vaunted 500 psi "spec compression" mark by rebuilding the leaking, but "younger" engine. Since I'm a fan of block heaters, this gave me a chance to check my "CPR" setup and method one more time, before the ultimate challenge:



OK. Since its NOT a turbo, as evidenced by the lack of plumbing when stripped of manifolds and starter: its not the ULTIMATE challenge. But,
if I do the "right design" of tool, I think, my setup will also be capable of accessing the plug for turbo-diesels. Ideally, with the turbo and its plumbing still in the car. Ideally.

By the end of the weekend, I hope to remove this plug, using the tool in this orientation:



.. using the knowledge gained, and some re-design from Trial #2, the subject of this thread extension.

While my Trial #1 setup proved adequate, there were two things I wanted to improve:

1) use a shorter bar. Certainly less than my 6' long tube extension.

The tool setup is shown below:


This shot shows the funky gas weld between the two sockets, which is actually a repair, from my effort to:

2) "harden" the tool setup such that I might consider loaning it for someone else to use.

During Trial #2, I decided to use the "old school" heating method , and figure out how to REALLY heat the plug.

So I hauled out my "gas axe" Oxygen-Acetylene rig, with a Victor #0 tip to allow me to spread the heat out to a "brazing" type of setup. My concern was overheating, and possibly softening the hex, or distorting the plug, such that the hex would break out before the plug would loosen.

The plug is tight for a couple of reasons that weren't apparent to me until I removed one:



The plug is a straight thread 38mm diameter, with a 1.5mm pitch. There is a sealing flange, but no "gasket" or sealing ring to speak of. Which means that the prevailing torque, and thread form must be tight enough to seal against leaks, slightly stretching the plug in the hole. I could probably look this up in Machinery Handbook; or if anyone knows where to find it in the service manual, point me to the page -- I have a hardcopy and will scan and add it to this thread.

Anyway, i started Trial #2 with the previous "propane" setup, only to shear my homebrewed tool, almost immediately. it broke at the weld, probably from poor penetration, and proceeded to "corkscrew crack" around the welded joint.

I decided to "fix it right", so after some lathe trimming to improve the "mating" between the two surfaces, and shorten the overall length; and making an "inner shaft" structure from a piece of 13mm hardened hex stock that now goes through the two sockets, and is welded to the 13mm x 1/2" base socket, with a pressed fit into the 1/2" hole in the 19mm hex;



and gas tacking, straightening on the lathe, and then fusion welding the seam in a spiral overlay -- I'm happy!

The application of "gas axe" heat surprised me. I thought, as I was spiraling the heat around the periphery of the plug, that I'd not have a problem getting the plug cherry red.

Wrong.

The heat soak capacity of the block is clearly HUGE. As fast as I could spiral, the plug would absorb it, draining the 1/4" diameter spot of heat into a smoking gray, hot plug. I didn't think to borrow a non-contact pyrometer for Trial #2, but this is in the plans for this weekend's "Ultimate Challenge"; so that I can record the temperature of the plug "at release".

"At release"? YES! To my amazement, after applying the gas axe for about 20 minutes --- the plug unscrewed! Using ONLY the service tubing extension,

and MODERATE torque input -- I'm guessing perhaps 150 ft-lbs, and I've done a LOT of torque wrenching in 40 years -- the plug came out without a hitch.

Another observation: even after breaking loose, I had to use about 50 ft-lbs of torque to unscrew it! Which tells me that its probably an interference thread, which makes sense in its "gasket-free" design. And partially explains why, when seized by time, acids, heat cycling, and galvanics -- its an
ULTIMATE CPR challenge!

[winmutt]

500psi *dream*.


And I was happy with 380 dry on mine

[mobetta]

If you need another one to practice on, I am not too far away.

but really- nice work, good info.

[whunter]

Originally Posted by franklynb

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

Please let me know if you figure out how to remove it with a "regular" length breaker bar!

The last one I did broke three special tools.
I used an oxygen acetylene torch, bringing the plug/block near cherry, 3/4 inch breaker with an eight foot cheater pipe attached to a chain fall, lifting a 300D two inches off the floor, jumped (250 LB) on the front bumper, then the plug moved (dropping the car).

This job is very high on the PIA scale!!!

[Chas H]

I made a 3/4" drive tool 25 years ago to remove that plug. The first tool was 1/2" drive and that sheared right off the first attempt. I have removed a number of plugs, without heat and engine in situ, using a 3/4" drive T handle and 6 ft pipe. The air cleaner needs to be removed and the coolant drained.

[strelnik]

I congratulate you.

Soon I will be installing several of these in late 50s diesels and one in an OM 636 diesel from the early 50s. Your advice will be oinvaluable.

I just need to get the dimensions right on the plug. If worse comes to worse, I may make my own design!

[showme]

Yep, that settles it. I'm a hoser. Nice job and nice post, though. Wish I had a garage!

[kerry]

Why not use a torque multiplier? Not sure if there's enough room with the engine in the car to get one in there but with the engine out, it would quickly increase effort.

[Mark DiSilvestro]

Eight years ago I did one of these on a 1980 300D. I removed the manifolds and used a piece of 3/4 hex stock, supplied by a neighbor that works at a machine shop.
The hex was Long enough to fit in the plug and leave enough exposed to be gripped by a 3/4 impact socket. The plug finally came loose with a 5-foot length of pipe on a 1/2" breaker-bar, without using a torch. I might not have attempted it had I heard any horror-stories about the possibility of cracking the block, but this forum wasn't around then.

Happy Motoring, Mark

[dabenz]

Ummm.... ....I didn't have problems, other than a bit of cussing and wiggling. When I removed daBenz's tank water heater (heater inlet came from that right rear plug spot) there was either an o-ring or a square gasket - this was about five years ago so you'll have to excuse my mad-cow. Same gasket when I pulled the normal plug from the parts car. I just checked my paper "catalog B" (the parts blowup) and there's a gasket in the diagrams for both diesel OM615 and gas M615 blocks. Can anybody confirm that there's NOT a gasket spec'd for the "newer" blocks?

The job wasn't too bad considering the plugs had been there a few decades - 1/2in by 18in swivel-head breaker from the top after removing the air duct, with a 3ft cheater all the way down the breaker handle. Used an extension to a long socket with the long part of a cut-apart L-shaped allen wrench taped to the socket. No heat needed (this time). Made an aluminum foil trough to keep the starter dry and used anti-seize when installing.

I've had the most luck when the very first wiggle is in the wrong direction - sometimes a finger-crosser when you know you're dealing with a tapered thread and you don't know if the other guy tightened it down too much. With a straight thread you're only dealing with corrosion, and it's time for the gas-rig if the first wrong-way wiggle doesn't work. I have "burned out" gaskets to make room for the oil on really stuck fittings.

Brass conducts heat twice as fast as for cast iron (or steel, in the case of something like a house water heater), so heat the brass. You want to quickly expand the plug and crack the corrosion before the hole has a chance to expand too much. This is the opposite thinking as compared to a stuck steel nut on a steel bolt or stud, where you heat the nut.

Never never ever ever hammer cast iron. You can weld a crack after drilling out the ends of the crack, but it's not fun and you'll never know how long it will last. Oil is a lot cheaper than replacing a small engine block. Cussing and wiggling are free.

[Admiral Ahani]

I eagerly await the ultimate challenge of doing this to a turbodiesel 617 in the car! I was about to install a block heater soon, but it really, really sounds like a giant PITA. Time to go buy a 6' iron pipe from Home Depot. Would an iron pipe be a good breaker bar extension? And would a Snap-on or Hazet 19mm allen socket work alright? (i.e. why did you use 3/4" welded to other sockets, etc?)