While we are on the subject, more or less, how smart is the GP relay?
Is it temp/time sensitive? Mine has since I've had it only shown about 5 seconds of the GP light, though there on for whatever time after there suposed to be(I timed it once). Seem's like my VW's would hold the light longer when it was colder. Or I could be makeing things up again.. :rolleyes:

This is entirely true, that is why YOU MUST test the glow plugs when the engine is cold otherwise they will give you a higher resistance value.
internal resistance falls as glow plug temp rises which leads to a lower current flow. a new glow plug at engine operating temp has a resistance of about 100ohms

You guys are great. I was able to note that #2 plug was not testing on the meter. Popped it out and bench tested it to 12v & ground. Dead. Found 4 old ones (didn't have a new replacement at the moment) and bench tested them to find a good one.

The interesting thing is that I just had put new ones in during 2003. This is quite exciting for me to discover an easier way to find one bad plug rather than simply throwing 5 new ones in all the time.

Looking forward to seeing how her car will fire. Should be 39 degrees tonight and that will communicate something.

Don

In using my multi-meter, I put it on Ohm's and at the 200 level.

Is it important that my TD tested in the 1.6 range for each plug (through the connector plug in the Glow Relay Box) and my DT tested in the 2.3 range?

Thanks

Don

At that range, the meter's accuracy is probably plus or minus 1 ohm. I wouldn't read anything into the 2.3 ohm measurement except to say that it is slightly higher than the other.

The Ohm measurement is a good rule of thumb test, measuring the current would be better. I've only just measured the resistance with a fairly decent meter and I've been fine, but if you still have trouble, I would check it like rwthomas said, but don't do it long, because it is supposed to run on a little less, like 11 volts. Two other things to keep in mind: 1. older relays vary considerably in how long they run, based on a charge of an internal electrolytic capacitor - they do change over time, as well as several different design iterations for venting etc. Fastlane sells an updated glow plug relay with 4 plugs at a fair price. This relay runs intermittently for up to 3 minutes in cold weather. 2. The glow plug indicator light is controlled by reed switches in the relay and the current of #1 plug is compared to the average of #2-5. based on variability of resistances MB claims that 1 or 2 plugs could be failed and the indicator wouldn't show it, either by not lighting or flashing etc. depending on your particular model

Snow and cold.
 

Getting cold out there.
How well are your glow plugs working?

Good question.
Anyone?

Hmmm
 

Mine is on longer in cold weather.
Perhaps you have bad glow plugs.
When I got the 1985 300SD, the light was on for five seconds, found three bad glow plugs, replaced them and all is normal.

The glow plug relays used up to about 1989 have a temp sensor inside the relay, that measures ambient temperature in the engine compartment. It will lengthen glow time in very cold weather. These have a maximum preglow time of 60 seconds and no afterglow. The relays from about 1990-up use an external coolant temp sensor in the cylinder head, which is much more accurate. These systems also have an afterglow function, which keeps the plugs activated for up to 180 seconds after startup (depending on temperature). This greatly increases cold-starting smoothness as well as emissions.

The inrush current is, IIRC, about 15 amps per plug. And yes, this decreases very quickly down to about 8 amps per plug. If you have a DC clamp meter you may be able to test current draw on each plug. The resistance check is very often accurate enough. Testing a loose plug will read 0.6 ohms with an accurate meter. If you test at the GP connector through the wires, the reading may be 1-2 ohms, which is still OK. If the reading is a few dozen ohms or higher, the plug is probably bad, or at least should be tested directly at the plug (with GP multi-pin connector unplugged!). Removing the plug and applying 12V would be the most definitive test, but that's a lot of work which shouldn't be needed.

FYI, for those of you with pencil-type plugs on the OM617.95x and vertical injected OM60x engines (tha's pretty much every MB diesel from 1980-1989), the correct plug is the Bosch Duraterm #80006, which also happens to be an afterglow-rated plug. Anyone interested in retrofitting a 'poor man's afterglow system' should read this thread thoroughly - preferably *before* asking questions that are already answered earlier in the thread. :D :D


HTH,

This is what the guys at the injection shop told me. They said it aint good until they see it glow.

Quality???
 

Yesterday morning three glow plugs on my 1985 300SD died.
I went out and picked up a new set, but the failed ones are less than fourteen months old.:mad:

Even if I must replace them twice each year, it is still cheaper than a gasser.:D

123 126 om617 preglow system
 

http://wagoneers.com/DieselBenz/TECH/PDFs/Engine_617_15-710.pdf

http://wagoneers.com/DieselBenz/TECH/MISC-INFO/124-series/W124/Index/MiscFiles/123glowS.pdf

Another thread to read.
 

Don't always trust your glow plug indicator light!
http://www.peachparts.com/shopforum/showthread.php?t=138347

resistance/heat
 

eskimo is correct. an unenergized gp is less than 1 ohm. as soon as current is applied the element heats and resistance goes through the ceiling. a simple experiment: take a short piece of copper wire and measure it's resistance, which will be very very close to zero. then have a friend heat the middle of the wire with a cigarette lighter and you will see the resistance increase incredibly. in the gp electric current takes the place of the cigarette lighter.