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  #1  
Old 02-23-2006, 07:33 PM
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Exclamation Glow plug stumper of the week

This thread involves my 1982 300SD. Last weekend it got relatively cold here in St. Lou. I had the car plugged in over night last Friday and drove the car to my cousins house about an hour and a half away. It was 5°F Saturday morning. Car started up without incident. I let the car sit out all day on Saturday. The high that day got to about 20°F. Tried to start it to go home about seven pm that evening and the engine turned over but would not fire. We tried jumping the battery to no avail. As much as I hated to do it, we used ether to get it running. At least I had assitance with the ether so I was able to crank while the help sprayed the ether. I was able to make it home with out incident.

I tried to get the car started on Sunday but no go. Luckily I have the Duramax to use as a back up. The past couple of days I was doing some trouble shooting and here is what I found:

When I engaged the ignition to glow the plugs, I could hear the relay coming in and it went out after approximately 30 to 40 seconds. The glow plug indicator light was not illuminating. Tonight I checked the resistance in the glow plugs and found the reading to be in the megohm range. This is not good. I just replaced the glow plugs earlier this past spring. I replaced them with new Bosch plugs. All five glow plugs were reading in the megohm range. I could not get the car to fire. Luckily I am somwhat of a pack rat so I saved the old glow plugs that I took out this past spring. I checked their resistance prior to installing them and they checked out at 1 ohm or less. I also changed out the relay box. I have a spare that I got from the junk yard. I thougth maybe this was the cause of the new glow plugs to go south. I also checked the 80amp fuse bar in both relay boxes for continuity and visually inspected for hair line cracks. They both checked out ok.

I also checked the voltage on the glow plugs while in the glow mode. All five were reading 13.7 volts. This makes sense I believe, because the glow plugs were not consuming any current because they were effectively open.

After installing the old glow plugs the car fired right up, as it is about 55°F here this afternoon.

Here is my delema. Why did the new glow plugs basically develop infinite resistance? And why did all five of them do this at the same time? Has anyone else experienced this? I think I have provided the proper sequence of events and detail. Could the relay have stuck and kept the new glow plugs energized until they burned out?

I am open to questions and comments. Should I see if there is any warranty on the new glow plugs?

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'93 GMC Turbo Diesel 1-Ton Dually 113K miles Stolen 17 Jul 05
2005 GMC 2500HD Crew Cab D-max 22K miles Love it!
'68 Corvair Monza 110 Coupe 26K Sold
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Last edited by Brian Carlton; 02-24-2006 at 10:30 AM.
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  #2  
Old 02-23-2006, 08:00 PM
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Bump

Where are all of you glow plug wizards?
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'82 300SD 206K miles Anthracite Grey received 250,000 Km badge
'93 GMC Turbo Diesel 1-Ton Dually 113K miles Stolen 17 Jul 05
2005 GMC 2500HD Crew Cab D-max 22K miles Love it!
'68 Corvair Monza 110 Coupe 26K Sold
'66 Corvair Monza 110 Convertible 123K
'52 Ford 8N Sold
'66 Ford 3000 Diesel (204 hours) For Sale
'86 White 2-65 MFWD Iseki Diesel
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  #3  
Old 02-23-2006, 08:16 PM
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Probably a few bad ones. It isn't un commen these days for Bosch glow plugs to fail pretty quickly.

Although all 5 going bad sounds a little fishy. Unless you had a few dead ones and didn't really notice until it got cold enough to actually need them.
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  #4  
Old 02-23-2006, 09:06 PM
t walgamuth's Avatar
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when i had the glow

timer stick it vibrated like crazy and ran my battery down.

there might be another way for it to fail that would burn the plugs out, too. i have not had that happen but i could imagine that it could.

tom w
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  #5  
Old 02-24-2006, 07:57 AM
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Any other

Opinions out there on why this happened?
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'82 300SD 206K miles Anthracite Grey received 250,000 Km badge
'93 GMC Turbo Diesel 1-Ton Dually 113K miles Stolen 17 Jul 05
2005 GMC 2500HD Crew Cab D-max 22K miles Love it!
'68 Corvair Monza 110 Coupe 26K Sold
'66 Corvair Monza 110 Convertible 123K
'52 Ford 8N Sold
'66 Ford 3000 Diesel (204 hours) For Sale
'86 White 2-65 MFWD Iseki Diesel
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  #6  
Old 02-24-2006, 08:18 AM
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Yeah. You shouldn't have 13.7 volts at the glow plugs, it should be 11 volts. However, with a set of "new" plugs all having developed high resistance, I can sort of see the tendency of the potential to rise to that. It shouldn't, which is why I would suspect a problem with the glow plug relay. Too much potential and current directed toward the surviving plugs once the first one or two stop drawing current probably fried the others in short order. FWIW, at one point I was convinced that both relays I had were bad for several reasons. But now that my engine has the compression it should, my relay is wonderful. Still, I would wonder about that relay. I think Phil sells a relay/plug set which is a good deal - a lot less money than MB was asking for NOS relay alone nearly 10 years ago.
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  #7  
Old 02-24-2006, 10:38 AM
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Quote:
Originally Posted by Pete Burton
Yeah. You shouldn't have 13.7 volts at the glow plugs, it should be 11 volts. However, with a set of "new" plugs all having developed high resistance, I can sort of see the tendency of the potential to rise to that. It shouldn't, which is why I would suspect a problem with the glow plug relay. Too much potential and current directed toward the surviving plugs once the first one or two stop drawing current probably fried the others in short order. FWIW, at one point I was convinced that both relays I had were bad for several reasons. But now that my engine has the compression it should, my relay is wonderful. Still, I would wonder about that relay. I think Phil sells a relay/plug set which is a good deal - a lot less money than MB was asking for NOS relay alone nearly 10 years ago.
Pete, if the plugs are all open (infinite resistance), there is no current flow, so the voltage at the plugs will be battery voltage.

Also, the relay cannot "direct" current to any of the plugs. The relay is simply a switch. The resistance of the plug determines the current flow. The relay cannot "burn out" the plugs with the only exception being that it remains closed past the 40 second limit.

I find it hard to believe that all five plugs would be defective and would fail at precisely the same moment. It's far more likely that the relay did "stick" once and leave the plugs on for an extended period of time.........something the plugs won't tolerate.

So, the proof will be on the next set of plugs. If they fail in short order......as a group.......then the relay must be changed.
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  #8  
Old 02-24-2006, 11:24 AM
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Interesting

As mentioned in my original thread, I have replaced the devective plugs with the old ones I took out last spring and I switched the relay box as well. Probably not good move for trouble shooting purposes, but I did not feel like switching back to the old relay box.

Just for the record, it was about 31°F this morning and the car fired up after a normal glow cycle.


It looks like the relay box is able to be opened up. Is there any thing to be gained to doing that and inspecting the relay inside? This just seems to be a weird isolated case.

Has anyone else ever experienced a similar situation?

Could it be that there is a manufacturing defect with this lot of glow plugs?
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'82 300SD 206K miles Anthracite Grey received 250,000 Km badge
'93 GMC Turbo Diesel 1-Ton Dually 113K miles Stolen 17 Jul 05
2005 GMC 2500HD Crew Cab D-max 22K miles Love it!
'68 Corvair Monza 110 Coupe 26K Sold
'66 Corvair Monza 110 Convertible 123K
'52 Ford 8N Sold
'66 Ford 3000 Diesel (204 hours) For Sale
'86 White 2-65 MFWD Iseki Diesel
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  #9  
Old 02-24-2006, 11:37 AM
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Quote:
Originally Posted by anhydrous7
Could it be that there is a manufacturing defect with this lot of glow plugs?

Certainly possible.........however, the chances of them all failing at the exact same moment are zero.

Did you see any difficulty in starting for the last several weeks..........maybe the glow plug light behavior had changed...........some symptoms that would have given you a clue that one or more glow plugs have failed?

We can analyze it to death.......but........the old set of plugs should let you know if the relay is the culprit. These things have a habit of returning. If the new "old" set burns out in short order, you'll have your answer.
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  #10  
Old 02-24-2006, 12:12 PM
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If you are brave and creative, try this:

Duct-tape or otherwise fasten a 12v lamp (or a voltmeter) to the dashboard where you can see it.

Connect the lamp, using long leads through an opening in the firewall, between one glow plug lead and ground. This lamp will glow (or voltmeter read 12v or so) as long as the relay is energized. Unlike the dashboard lamp which goes out by time, this will definitely tell you if the relay remains on too long.

If the lamp 'sticks' on after you start, the relay is 'sticking' and you may get a chance to the relay before you burn out another set of GPs.
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  #11  
Old 02-24-2006, 02:57 PM
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That's a good idea. I think I'll do that after I finish testing/replacing my plugs this weekend. Maybe I'll save myself $65 in yet another set of plugs.
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  #12  
Old 03-03-2006, 12:00 AM
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is any one willing to donate thier old glowplug relay? im looking for a dead relay that is supposed to stay on after u start you engine for a litlle while in order to come up with a diy repair on these things...i have already started on one that doesnt have the feature and was able to get it to work but i need to see the difrence in the two designs....thanks ~Luke
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  #13  
Old 03-03-2006, 11:29 AM
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I would urge you to R&R the glowplugs with new plugs, why try and save $40 by using old ones? Also, I read a while back that the newer glow-plugs are less likely to suffer the failure you are describing, because when they are combined with the new relay- the deposits of gunk that cause them to stay hot too long (and fail) are burned off quickly- prolonging the life of the plug.-J
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  #14  
Old 03-03-2006, 03:04 PM
RAYMOND485
 
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Glow Plugs

1984 300d Turbo
Ream The Glow Plug Holes, Tool At ************************, The
Carbon Overheats The Glow Plugs And Burn Out, Plus The Carbon Stops The Heat Transfer To The Pre Heat The Cyl. Auto Zone Have
Glow Plugs Check On Line,
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  #15  
Old 03-03-2006, 07:00 PM
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Absence of Water - Did you ream those glow plug holes?

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