Hmm.. so today, the glow plug light would not light.

#1 Looking at the service manual, I have a few questions. It said to test the glow plugs by taking a screw driver to bridge the contact bars to determine which plug is faulty. So I'm guessing no worries on electrocution here?

#2 Removal steps state that you would just unscrew them. Looking at it though, it looks like 2 and 3 are partially blocked by the injector pump. Correct? That must be a pain to remove all of that.

#3 Last, what's the current belief on reamers? Necessary evil or nice-to-have if you want to be gentle for another 30,000 miles?

Thanks all.

Do you have the original loop plugs or the newer pencil upgrades?

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I think original. Any tips on determining their type without removal?

I'm guessing they are loop as it takes 45secs to get going. This is in 70F summer weather here in NorCal. Google results are suggesting upgrading to pencil improves warm-up times.

Easy to tell, if you look between the glow plugs and see squiggly copper wires, they are loop.....if you see standard electrical wire they are pencil.....they heat up a hell of a lot faster and if one dies, they don't all go out as with the loop style...

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My closest experience is on a w115 220d, so take my advice with a grain of salt:
1) Use a volt meter while a friend activate the GPs. On my 220d, the voltage arrives at the rear of the engine and ends at the block in front of GP1. So starting at the back, check voltages along the way. Normally, it is about 1V drop across each GP, and 2 V drop across the wiggly connector bars/wires. This allowed me to determine the first GP that had problems. I ended up changing them all out, so this info was academic in the end.

2) On those two middle plugs, the IP is in the way enough that you cannot easily use sockets. So I bought a regular box wrench for those. It was slightly slower and meant I could not torque them going back in, but was no big deal.

3) The loops kind of do a little reaming as you pull them out. The reamer for the old loop plugs is not cheap. I did my best with a screwdriver.

You can read about some of my experiences here:
Glow Plug Replacement: a beginner's perspective
and
Beru loop style glow plug source?

In post 11 of that second thread, I give the dimensions of the official MB reamer for the 220d OM615.

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1968 220D, w115, /8, OM615, Automatic transmission.
My 1987 300TD wagon was sold and my 2003 W210 E320 wagon was totaled (sheds tear).

I'm not seeing what you described, but perhaps I'm not looking in the correct location.

Here's a picture. Any idea on loop or pencil from this shot?


Thanks again everyone. Shortsguy1 -- you're linked articles were VERY helpful. Thanks for sharing those.

Those GPs are in series. They are the older, loop style GPs. You have straight bars between most of your GPs, whereas I have these odd bars that wiggle up and down (mine aren't copper though). So the voltage drops that I mentioned may not apply directly, but the concept should still work. Your voltage comes from the back of the engine and travels towards the front, passing from one GP to the other. You can just barely see the grounding strap between the first GP and your block. It is hiding behind a fuel hose which has a zip tie on it to the left of your photo.

I would replace all four while you are bothering. It really isn't hard once you get the gist. While I had mine apart, I sanded all of my connectors a little to clean off 20 years of junk. The first time I did it, I skipped this step which was a mistake.

I am actually amazed how fast the system warms up even though it is in series. My indicator (which is a glowing resistor in my dash) starts to glow after about 10 seconds. Before I sanded everything to clean the connections, it would take 20 seconds or more to even start glowing orange.

I have decided to NOT upgrade to pencil plugs because I like my quaint little system. It works fine for me, so it is not worth the cost of changing it. Others here definitely prefer pencil plugs, but honestly, if the 10-20 seconds of time difference really mattered, I probably wouldn't own a 45 year old car with a 0to60 time of nearly 30 seconds.

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1968 220D, w115, /8, OM615, Automatic transmission.
My 1987 300TD wagon was sold and my 2003 W210 E320 wagon was totaled (sheds tear).

Thanks! That 3rd GP has me worried. I don't know how a GP could possibly be removed as the coolant line to the heater core (I'm guessing) looks close.

Ugh.. wrenching on a hill on the street is going to be annoying. Hoping for the best.

Hmm. I might have dodged a bullet. I went out with my helper to give it a test to determine the bad GP. The "salt shaker" lit up. I guess she just didn't want to move on Sunday. Perhaps she was praying to Jesus or something.

Do these things get fickle when they are about to go?

I did experience "fickle" electrical connections before I cleaned everything. If it wasn't working, I would get out and tighten one of the small nuts (which hold the wires on). Often it would work after that.

So if time allows, maybe clean (steel wool? sand paper?) the connectors to see if that eliminates any fickleness. But if it is working and continues to work, maybe it is best to leave well enough alone. I find that sometimes I create more problems than I solve when I tackle non-essential repairs.

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1968 220D, w115, /8, OM615, Automatic transmission.
My 1987 300TD wagon was sold and my 2003 W210 E320 wagon was totaled (sheds tear).