I would like to get an early start at checking out my glow plug system before cold weather descends on Northeast US, so I have a couple of questions. Like my signature says, we're talking about the '84 300SD with an OM617 turbodiesel.

About 3 years ago, I took her to the dealer to get the valves adjusted and have the glowplug system checked out. They said valves were mostly within spec, just a couple that were a little tight. They tested the glowplug system and replaced 2 glowplugs. They also reamed the glowplug holes.

The car had improved starting that winter after the repair but has deteriorated since (as has the fuel mileage, too!). It's possible that mileage deteriorated because I need to move my car every couple of hours where I work because of a stupid parking situation. Anyhow, she'll do ok down to 28-30F ambient maybe. At 24-25F, I may be able to get her to start, but she struggles and has to crank a lot. Below that, I absolutely must use the block heater if I want her to start in the morning.

Couple times when I couldn't get her to start cold after much cranking, there was just a bunch of smoke out of the tailpipe, like ashy-gray colored smoke. Also, when I start hot, there's often a small puff of gray smoke.

Anyway, short of messing with the injectors or IP timing right now, I'd like to get the "easier" stuff out of the way.

Cold battery measures 12.75V post-to-post. Voltage at the glow plug relay fuse read 12.25V against battery "-" terminal, and voltage at each relay pin when relay was on read also 12.25V against battery "-" terminal. Weird, I thought, why the 0.5V drop? So, I measured voltage drop between relay fuse and battery "+" terminal, and it measured 0V... Maybe some contact points I was measuring were slightly oxidized or something. I'll have to measure some more later. Each glow plug tested about 1 Ohm.

Eventually, I want to pull out each glowplug and see how it glows when I turn the key, to make sure it's hottest at the tip, but in order for me to do that, I need to have a reamer on hand, which brings me to the next point:

I would like to ream out those glowplug seats, as I'm sure I got a lot of carbon in there, but don't have the money to invest into a proper reamer tool for this engine. What size is the bore (mine should be pencil-type plugs, right?), so I could get a plain reamer from a tool supplier?

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84 300SD - bought in April '06 with 237,000 mi