The old glow plug is still in the head. At this point it's not worth the frustration to me to attempt getting it out.
He tried getting out another glow plug and it broke off as well, he then welded a bolt to what was left of that glow plug thinking he would have something to grip, that broke off at the weld so now there are two plugs stuck in the head and the remaining 4 are so tight in the head he gave up.
The engine runs great and has been so reliable to me but the car body is so badly rusted out it's time to replace the car rather than sticking money into it to remove glow plugs.
I'm looking for something with a turbo this time around and pre CDI whatever year that would be. Too much computerized stuff is not for me, I am old school!

Does not sound like he was the right guy for the job. Hey, you do what you gotta do. It's your car and only you know best. Good luck!

__________________
85 300D turbo pristine w 157k when purchased 167,870 July 2025
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

Thanks funola.
Pulling out the engine to replace the glow plugs just seems crazy to me.
I just feel there is a design flaw there somewhere that they get stuck in the first place. I think glow plugs should be as easy as replacing spark plugs in a gasser and why would you design the intake manifold around them so that such a simple would be job is so labor intensive?
I used to drive VW diesel Jettas and glow plug changes were a walk in the park.
Okay, I'm done venting!

I would not call it a design flaw. The glow plug has gotten longer and smaller in diameter with newer engine designs but the way they seal via the flare is the same. I think the problem is due to improper installation when the glow plugs are changed, due to debris between the sealing surfaces or improper torque. This allows carbon to breach the sealing surface and pack the area between glow plug body and head cavity. The smaller diameter and longer glow plugs are just more prone to breaking when packed with carbon and ham fisted mechanics/ DIY try to remove them using bad techniques.

__________________
85 300D turbo pristine w 157k when purchased 167,870 July 2025
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

More to the point - the OM606 is a DOHC design with the prechamber centered in the cylinder head. Arguably a better design than the SOHC design with the offset prechamber of the OM603 that preceded it - better breathing and better / more complete combustion. As a result that glow plug has to be pretty long to actually get to the prechamber, it isn't right up against the side of the head like the earlier engines were.

Just be glad it isn't the 2-piece spark plug that Ford used in the mid 2000's V8's. THAT was a stupid design!

__________________
Current stable:
1995 E320 157K (Nancy)
1983 500SL 125K (SLoL)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

Gone and wanting to forget:
1985 524TD 167K (TotalDumpster™) [Definitely NOT a Benz]

Don't get me wrong guys, I'm a Mercedes diesel enthusiast just like you and I would never go back to VW after owning my first Mercedes.
If the timing belt breaks on a VW the engine is toast, they are zero clearance engines, the valves smash into the pistons and it's all over. It happened to me and that's when I decided to give Mercedes at try.
I love my old '95 E300 and I guess I should be happy it has been so reliable to me for so many years. This was my "learning" car!
I am looking for something to replace it (Mercedes diesel) for sure and hopefully I will find something with a turbo this time and glow plugs that were replaced properly.
funola explained how the glow plugs should seat in the head and I took a close look at mine and sure enough they were screwed into the head at different depths. some were in fairly deep and others were not.
I will be be waiting for an analogy on my first Mercedes experience from dieseal300 (he is pretty good at that) The one about the lift pump acting as a mini air compressor was perfect!

Did someone say analogy?

The seal on the glow plug is the same concept as the prechamber seal. The implementation is nearly identical to that of a flare fitting in plumbing. You have a tapered seat that a machined fitting is pressed against for a tight metal-metal seal. They work very well, but are critical that the sealing surfaces are clean and the connection is tight. See this picture for a visual on a flare:


The actual "flare" is in the cylinder head and the "fitting" is your glow plug threaded into it. Any rust, carbon, or other garbage left on that sealing face will prevent a good seal. Over time the seat will start to leak just from differential expansion and having all that hot exhaust gas pressing against it. Eventually some "gunk" will get out and get the glow plug stuck. It hapens on the earlier engines too, but with their short glow plugs, you don't have to worry too much about torquing them in half. With the long skinny plugs used in the 606, it's more of a problem. There have been threads on here on how to grind off the threads from a glow plug and cut a notch in the sealing face to follow up behind a glow plug reamer to re-dress the seat.

I'm personally not a fan of VW products. I don't like the way they drive and I don't like the way they're engineered (they seem to have way too many expensive problems). For the cost of the car when new, you'd expect better. The newest VW I've driven was a 2014 Passat with the 2.5 5 banger. HATEFUL car. Uncomfortable driving position, a truly gutless engine, transmission that always wanted to be in 5th gear even when stopped, steering that felt like grabbing a marshmallow, and a suspension that managed to be both soft and sloppy AND choppy at the same time - have NEVER experienced that before! I've been spoiled by driving decent cars, so my standards are probably higher than they should be, but I haven't and won't own a VW.

__________________
Current stable:
1995 E320 157K (Nancy)
1983 500SL 125K (SLoL)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

Gone and wanting to forget:
1985 524TD 167K (TotalDumpster™) [Definitely NOT a Benz]

Another perfect analogy,"the flare fitting in plumbing".
I finally got a chance to read the write up on your first Mercedes, very interesting. You mentioned doing a "diesel purge" at one point and I have heard of that before. What is the purpose of doing that and is it something I should be doing?

My "first" Mercedes is the 500SL. I still need to do a writeup on that one. 19 years of pain and elbow grease with that car.

The Diseasel got a "diesel purge" to clear the crap out of the injection pump. To be honest, I haven't really noticed much of a difference before and after. That said, my engine isn't the world's best example either. Some say it helps, some say it doesn't. It did get some nasty garbage out of the pump (used injection pump). I'd say if it ain't broke, don't fix it.

__________________
Current stable:
1995 E320 157K (Nancy)
1983 500SL 125K (SLoL)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

Gone and wanting to forget:
1985 524TD 167K (TotalDumpster™) [Definitely NOT a Benz]

I finally got my new fuel thermostat installed and thought my problems were over. The air in the clear lines is gone but when I shut the engine off the fuel in the clear line from the heat exchanger to the pre filter drains back after about 15 minutes and all the other lines remain full of fuel.
While the engine was running I noticed two of the delivery valves were weeping fuel so I blew them off with compressed air to dry them out but after a few seconds they were wet again. My question is, can I replace the rubber "O" rings under the delivery valves to stop the leak or do I need to replace the copper seals as well?
If "O" rings alone are sufficient , what size are they?

Thanks,
Rick

You have an air leak somewhere between the fuel preheater and pre filter. Those lines should remain filled.

The delivery valves should have the copper washers replaced along with the O-rings. The forum sponsor has the parts on their website. Poke around the forum for some very detailed threads on how to do the delivery valve seals. There's a specific tightening procedure.

__________________
Current stable:
1995 E320 157K (Nancy)
1983 500SL 125K (SLoL)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

Gone and wanting to forget:
1985 524TD 167K (TotalDumpster™) [Definitely NOT a Benz]

If there is a leak anywhere ahead of the pump fuel will drain back when switched off, my 606 has an MB non return valve fitted, not sure if factory or not.

__________________
David


1996 Mercedes S124 E300TD - 129k - rolling restoration project -

1998 Mercedes W210 300TD - 118k (assimilated into above vehicle)

It is hard to determine where the leak is that causes a drain back. It could be from anywhere in the fuel system, above or below the level of where you see the drain back. Think of it this way, when fuel leaks out, no matter how small, it is displaced by air, which slowly works it's way to the highest point in the system. Your best bet is to fix any visible leaks first, one by one, till they no longer weeps, and see if that cures the drain back. If the air bubble/ drain back is still there, keep looking. A diesel fuel system should be totally dry, you should not see or smell any diesel.

__________________
85 300D turbo pristine w 157k when purchased 167,870 July 2025
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

I have that same (check valve ?) in mine. I removed that hose and blew in both ends, free flow from filter to tank and restricted in the other direction so that seems to be working fine.

My delivery valves were leaking and I replaced the "O" rings today and that fixed that problem. I noticed that the fuel only drains back about an inch now in the clear line from the pre filter to the heat exchanger where before it almost drained back completely.
I'm tempted to squirt soapy water on every fitting and look for bubbles but I'm sure if it were to get sucked into a fitting that would be bad!
With all new clear lines it is much easier to see the fuel in the lines and I still see bubbles in the two lines on the lift pump. you can see it pulse with every stroke of the pump but it is much less than it was in the beginning.
This has really turned into a very frustrating project, I replaced both rubber hoses (feed and return) and hose clamps and all clear lines including every "O" ring (total of 18) and a new fuel pre heater that was cracked and leaking fuel.