be VERY careful guys with heat on a block side. it's fine to heat the brass, and it's fine to get a bit of heat into the block, but IF you are going to be setting a torch in a rig to maintain heat for a long time, BEWARE!!! cast iron will crack. it will get hot, and cool too quickly and crack. I would not get the block anywhere NEAR red hot. and if it cracks, and you "drill the ends of the crack" and try to weld it, you will be looking for a few more cracks. you can gas braze brass solder a crack, but it's really not a good plan. better plan is to keep the heat moderate, and never get the block near red hot.
J.M. $.02...

I have done this twice, and have had good results both times.
I also used a short piece of 3/4" hex stock. I inserted this in a 3/4" drive 3/4" socket with a LONG breaker bar Probably 36". I drained the block, so that I could get it hot enough using my MAPP gas torch. I positioned myself so that I could give short "bursts" of torque to the bar. Three "bursts" and it was off.
I think that the key is having rugged tools that can adequately transfer the force where it is needed. Even a 1/2" drive socket will flex substantially.
Give that I had the air cleaner/manifold/turbo off for gasket/seal replacement, The plug removal took about 30 mins.
It seems hard, but compared to working on old, rusty heavy equipment, it's a walk in the park.

Ja, it was pretty rough...
 

Just ran across this thread and after my experience thought I should chime in. I already had a block heater installed, but it was bad (I thought). It tested open with a meter from the plug, but the cord was a little ragged, so I clipped it off close as I could from above and tested again and still open.

My water pump went out and it was fall, so first winter with the car was in mind and I figured I'd better go ahead put in a new one while the coolant was out. Found a local Benz guy that had one available.

VERY tough to get to being under the turbo and above the starter.

The heater obviously did not have the inside hex due to the connector on it but had a large outside hex. Borrowed a 3/4" socket set, but 1-3/4 didn't fit and 1-7/8 was too loose. OK it's metric, apparently 46mm. Where do I get one of those? Turns out 1-13/16 is VERY close but why would anything SAE actually need that size? 1/8 increments ought to do it one stuff that big. Fortunately this was not the case. Northern Tools had 1-13/16 and was happy to sell me one. Also a short extension as the thing is too far in over top of the starter, but not far enough for the longer extension in the set. But still have to use the breaker bar at a slight angle. Can't quite get right angle for the ratchet.

VERY challenging crawling under the car and getting it all in place and then setting up to torque on it. Have to turn the steering wheel to move the linkage somewhat out of the way. Lots of fiddling and frustration. Hard to set it all in there and hold it in place, let alone be able to apply torque. Have to brace the extension with a chunk of wood against something (turbo?) to stay in place.

You'd think a breaker bar for 3/4" would be plenty long (about 2 feet!) to bust it loose. I braced myself with my feet and gave it all I had with both hands. No go. What do I do now? No room under the car for a cheater bar (without digging a hole in the driveway). Finally hooked a small ratchet strap to the tow hook on the front bumper and to the end of the breaker bar. This finally made it move.

There was JUST enough room to get 1/12 of a turn. Release the ratchet strap. Everything falls out. Replace the socket, breaker bar, wood block again (a very fiddly process done mostly by feel). Hold it with one hand, try to hook up ratchet strap, but it falls out again, so several attempts needed. One more 1/12 of a turn. Repeat this process many times. Finally is loose enough I can turn it with a 1/2 ratchet (glad I got the 1/2 to 3/4 adapter at Northern also!).

That has got to be the toughest thing I've ever done on a car!

After all that, the heater tested good on the bench!!! Turns out the cord was bad right in the connector. The new one (Zerostart) had a different connector, so I could not have swapped just the cord anyhow.

But there ya have it. Use a 3/4" breaker bar (with short extension) and a ratchet strap!

Sounds like it might have been easier to pull the manifolds, if not for the extra turbo plumbing.
My non-turbo TD started easily on the glow-plugs in 20 degree temps this week, though it idled very slow for a few minutes. My manual idle control doesn't seem to be working so I'll need to deal with that after it gets warm enough to work outside again. It was around 10 degrees this morning and I don't torture my diesels at this temperature. Don't need to go anywhere that early anyway, and have a newer gasser if I did.

Happy Motoring, Mark

Unless you live north of the Arctic Circle, a lower radiator hose heater is an adequate replacement that can be installed in 30 minutes without the use of a trucker's vocabulary.

+1

I have a 1500w heater . . . works well when I remember to plug it in!

I have just traded a small box of older comic books for a 5' long 1" breaker bar with 1" to 3/4" reducer, so now I just need a short socket and a short piece of 3/4" hex. I have five to do, but have to work this entire weekend. I saw this and thought about the task, am looking forward to it.

The plan is to heat the engine to operating temp, turn it off and put my son to work... :D:D

Lazy
 

Don't want to tempt another cardiac event.. :eek:

Call me if you need help.. :)

NOTE: Local MBCA meeting tonight.. ;)

I wonder how effective a radiator-hose heater would be on my W123 diesels, as both radiator hose attach at the top of the engine and the flow from the lower radiator hose would be blocked by the cold, closed thermostat.
I do have a 1500 watt heater that has nipples that would fit one of my heater hoses, but I worry if that would be way too much for my 240D or 300D. In any case, as I said before, I have other vehicles, so I don't really need to stress my old diesels at sub-freezing temperatures.

Happy Motoring, Mark

They are quite effective in the lower radiator hose. Not quite as good as the OE heater in the block but good enough to warrant avoiding any work on the plug or OE heater. I have one in my 123 and 116. It'll be 8 below zero in the am and I'm confident both will fire right up.

Edit:
It was 17 below zero this morning and the 116 with a lower radiator hose heater started right up. Didn't try the TD until later in the morning.

Anyone know if there were two types of block heater?

I had the engine swapped on my '85 300D and it seems the replacement block's heater does not match the cable's end fitting. It does plug in, but there is nothing to keep it there. The heater in the block is fine and the cable is intact - it just won't stay in place.

Here are some pics that might explain this better:

Answer
 

Yes, there are other cords.






.

OK Thanks - I will see if I can get the right one.

Related data
 

installing block heater. where to buy 19 mm allen key?
http://www.peachparts.com/shopforum/diesel-discussion/240529-definitive-block-heater-coolant-plug-removal-thread-post2052736.html

So how much trk is required to remove the pulg. That is the real question. Tell me how much trk to apply to break things free. I also think a good flush of the coolant system wil help be removing excess scale from the inside of the cooling system.

I slammed it with a 3/4 IR 2131 titianium that can crank out 1000 Ft/lbs and it did not budge. I use a MAP gas touch and heated the plug and area around the plug for a good 20/30 mins with no luck. I also used aa 30 " 1/2 ratchet from Matco that can break stuff loose the gun can not. (Head bolts on a race truck) I'll head over to harbor freight to sanm a long breaker bar. I like instant heat on a cold day.

Keep the tips coming as I'm going to try this tomorrow.