I want to tell any newbies to diesels out there about my experience. I bought an 83 240D in early September. It has always started fine in our somewhat warm but variable Memphis, TN climate. It was always rough on startup but smoothed out after 30 seconds or so. A couple of weeks ago, on our coldest day (the first full day it didn't get above freezing), my car would not start no matter how much I cranked it. I first suspected my glow plug relay, so I verified I was getting voltage to each glow plug and I was. I finally had to get starting fluid to get it home. After fiddling with this thing for a week, I broke down and bought four brand new glow plugs from Autozone ($10.99 each for Bosch). As I took each one out, it dawned on me that they are basically like a light bulb in that they have a filament on the inside of each plug. I tested each one for continuity using the "ohm" setting of a DMM, and found that three out of the four would not pass voltage through them! I still have the cuts on my hand from changing the glow plugs out as it is a PITA to get to all of them out because of the injector lines. However it was worth the pain. It was below freezing when I changed them out, and the car fired up to a smooth idle after 20 seconds of glowing. Car starts impeccably now. Take home lesson is CHANGE YOUR GLOW PLUGS if you haven't already. They are just like light bulbs - they have a limited life and do burn out.

Yea I planned on testing mine today. For everyone's reference the accepted resistance values are from .5 to 1ohm of resistance, anything more and that filament is going out on it. Starting fluid is a pretty bad idea generally, at least your GPs didn't work. The starting fluid could ignite when the GPs light, this would finish the GPs off.

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Jeff M.
Mercedes W123 DIY pages are now located here.
1983 / 1984 300D Sold
2000 CLK430 Cabriolet ~58k Sold
2005 Avalanche 4x4 ~66k

is there a way to check condition of the plugs without taking them out?

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Jennifer
90 350sdl

See above. Remove wire from GP and use mulimeter to test resistance between a good ground and the bolt on the GP.

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Jeff M.
Mercedes W123 DIY pages are now located here.
1983 / 1984 300D Sold
2000 CLK430 Cabriolet ~58k Sold
2005 Avalanche 4x4 ~66k

You can check the continuity of parallel - wired glow plugs by removing the connector that is located at the very front of the glow relay assembly. On the OM671.95X engine, it is a 6-pin connector with only five connection locations populated. Each pin in the connector goes to one of the glow plugs. Test continuity/resistance by connecting an ohm meter from each pin to ground.

I do not know if the OM616 (240D) uses the same relay but, if the plugs are parallel units, the testing procedure is fundamentally the same.

Note:
While an open circuit glow plug is definitely a sign that the plug has failed, a 'non-working' glow plug can still have electrical continuity. The FSM test for proper glow plug operation is based on the current draw, not continuity. Unfortunately, not many of us have DC ammeters capable of reading anything but milliamps.

The lovely and charming Marlene went through this last month when we first started getting cold weather. At 35° F it took several glow cycles and lots of cranking to get her attention. Ohming the plugs didn't reveal much, all had continuity but, one plug had slightly higher resistance than the other four. I replaced that one (per PEH GP replacement guidelines) and haven't had a bit of trouble since then.

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Never a dull moment at Berry Hill Farm.

I was wondering whether I could do it a quicker way, however I still plan on taking those lines off so I can put some die-electric grease on them to make sure the contact resistance is as low as possible. How much higher was that one GP? I would have replaced them all, but that is just me. I mean if only one cylinder was giving a problem then I could understand but it'd still run then, just very rough on that one cylinder.

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Jeff M.
Mercedes W123 DIY pages are now located here.
1983 / 1984 300D Sold
2000 CLK430 Cabriolet ~58k Sold
2005 Avalanche 4x4 ~66k

All of them were 1.0 or .9 on the multimeter, however what I wonder is should I subtract off the .6ohm resistance if I were to connect the empty leads together?

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Jeff M.
Mercedes W123 DIY pages are now located here.
1983 / 1984 300D Sold
2000 CLK430 Cabriolet ~58k Sold
2005 Avalanche 4x4 ~66k

On the lowest ohm scale that my digital meter has (2 ohms full-scale), four of the plugs were reading .03 and the bad plug was reading .05 ohm.

Those numbers sound weird compared to the information above and, I'm pretty suspicious of the accuracy of my meter measuring low impedance circuits. However, the important thing here is comparing the relative resistance readings and looking for the outlier.

Maybe one of these days, I'll buy one of those snazzy FLUKE meters and get a high current DC amp adapter. That way, I can check 'em properly.

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Never a dull moment at Berry Hill Farm.

Just forget about resistance testing pin type glow plugs. It's a waste of time. They can show acceptable resistance readings and still not work properly.

I expect that the reason for this is that they corrode internally which prevents heat trasfer to the shell.

When your pin type glow plug car gets hard to start or won't start at all, verify that there is voltage at each plug and then replace ALL glow plugs.

I have almost twenty years experience with pin type glow plug MB diesels and I can promise you that this is the case.

Merry Christmas

This applies to other diesels too -- I'm about to go and put a freshly charged battery into the Volvo to see if I can get her lit -- failed to start last winter and I've been kicking it every since. Over the summer I put a new starter in it as the old was seemed slow, and reset the timing (and HUGE PITA on this car, cogged belt drive, etc).

Still no go, and the sputtering I had last year went away, too. Finally decided to replace the glow plugs (I didn't before because they pulled plenty of amperage when I jumpered them -- on the Volvo TD there is a buss strap between all the GP). Well, what do you know, when I checked the old ones, one had the correct resistanc (either #1 or #6, it was late), one was open, and the other four read 0.00 ohm! Why do I wonder that it wouldn't start -- one glow plug aint' gonna do much a 0F!

Hope this fires it up, I hate to drive the 300D to work.

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!