A while back I was whining about a no start/occasional start condition. All evidence pointed at glow plug failure. BUT, I had replaced them about a year and a half ago with, presumably, good Bosch France gps, along with the relay, so I had doubts and wondered if something else was up. Anyway, it was the gps and a postmortem revealed that only one of five was glowing, and maybe a second, intermittently. Its a wonder the thing started at all...on two plugs near as I can figure. I put new ones in and it starts within one second of cranking like it did before.

Question is, were they just poor quality plugs to have under a year and a half service life or is there some underlying reason why they go bad? I realize they live a hard life, but I can't believe this thing came off the line 25 yrs ago with gps that had to be replaced every couple of years, at max.

And a followup question, how soon should I plan on replacing the Autolites that I stuck in it because they were locally available (I had to go somewhere)?

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1983 CD
1958 Studebaker Packard (being resuscitated)

Autolites are ok. The Champions are the ones with the short life. It sounds to me like you got a bum set though.

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1959 Gravely LI, 1963 Gravely L8, 1973 Gravely C12
1982 380SL
1978 450 SEL 6.9 euro restoration at 63% and climbing
1987 300 D
2005 CDI European Delivery
2006 CDI Handed down to daughter
2007 GL CDI. Wifes

That makes me feel better. At least I know the symptoms well now and I think I can detect when its time to do it again. Seems like somebody was trashing Autolites not too long ago, though.

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1983 CD
1958 Studebaker Packard (being resuscitated)

Its not a light bulb, its a fairly critical engine component in a high quality vehicle. Not really the same question, though I see your point. I find it hard to believe you can diagnose a bad plug and switch it out in five minutes, but I shall make that my goal!

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1983 CD
1958 Studebaker Packard (being resuscitated)

Boy, I'm glad we got that established!

On our 616's and 617's it is a very quick swap of the glow plugs. Uhm, that is unless you drop a nut down in the IP no-man's land........
Always put a towel under the GP you're working on.

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Jimmy L.
'05 Acura TL 6MT
2001 ML430 My Spare

Gone:
'95 E300 188K "Batmobile" Texas Unfriendly Black
'85 300TD 235K "The Wagon" Texas Friendly White
'80 240D 154K "China" Scar engine installed
'81 300TD 240K "Smash"
'80 240D 230K "The Squash"
'81 240D 293K"Scar" Rear ended harder than Elton John

Definitely put some catching mechanism. I dropped a nut and washer down that abyss when I replaced my glow plugs and had to go to the local hardware store to get some--which took forever to find because they're special, super-expensive "metric" nuts. (I paid $1.50 for that tiny nut!! All other nuts were around $0.20.)

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1983 300SD (W126, OM617) with 404k miles!
(OK, so the engine was replaced at 147k mi)

OK, I just meant it's really nothing more than a little heating coil and it will have some random probability of failing at any time (like a light bulb). They are very easy to diagnose/fix on a 616/617. You can usually feel when one is gone by the slightly rough start. I've always been able to identify the bad one with a multi-meter from the relay plug. If you have small enough hands and don't remove the injector lines, changing on GP is very quick (remove the nut and don't drop it, loosen the GP with a small wrench, spin it out with your fingers and replace). It's the kind if thing I will stop and do if I happen to notice one is out when I'm leaving home (if I have 5 extra minutes and I don't want to have to wait for the engine to cool off later).

With parellel plugs it is usually just a slight inconvience at worse if one plug burns out. On that series plug car of ours it's different. I always keep a test light, wrenches and one spare plug in the trunk. A failure of one plug can make the car into a non starter. The chances of someone locally having one on hand when really needed is pretty small..
If really stuck I guess you could undo the heavy bare feeder wires at one open glow plug with the series type. Short them together prefferably on the plug if possible to bypass the one burnt out plug to get you running. You still need a test light or meter to find the open plug though. Or carry a heavy wire with two strong clips to circumvent the open plug. We are dealing with a heavy amp flow here. Use the original size of the series harness for a size example.
Or just carry the right size nut, bolt and washers to temporarily tie the wires together. It's hard to think of quick solutions when confronted with a problem on the spur of the moment sometimes. .
The loop series plugs might be a little more reliable than the pencil type but do fail as well.
I am well aware the pencil type of glow plug set up does seem to do a better job of starting than the older loop plugs. Yet with a good tight engine the series plugs will do the job.
Also I have found over many years experience. If you replace the burnt out plug with a new one. There seems to be about a fifty percent chance it will burn out again at some point before another one of the old ones do with the pencil type. So I have always wondered if it was a quality control problem or some internal cylinder condition exists. Like a different spray pattern on the injector for example. Creating a somewhat different operational enviroment in that one cylinder for the plug.

me ^_^... I don't trust any part from autozone or the other mcparts store...

keep it german buy OG (original german)

Last time I went to the dealership to buy my wheel chocks I asked out of pure cureosity if they had any NOS glow plugs from the 80's.. sure enough.. they had a few that were still hanging around. I bought one... so I have a NOS glow plug for some form of diesel

This is a little like asking when a light bulb is going to burn out. On your car they are very easy to replace. I just wait until one burns out and replace it. You can tell when a single GP is out by a little roughness when it starts. I usually have one or two in my trunk, when one fails, I spend 5 minutes and replace it.

What I was actually trying to get at was some comparative experiences with glow plug longevity, German, French, or trashy American chain parts store...whatever. Is there a brand/providence that folks swear by because they last a long time (and I am sure there are some opinions)? And, is there anything other than manufacture quality, or lack of, that contributes to their demise. The tip of one of my Bosch's was burned off, the others were just non-functional, except that one.

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1983 CD
1958 Studebaker Packard (being resuscitated)

Glowplug life varies quite a bit - one of the more significant factors is the service environment of the car. Short trips mean more start-ups per mile and subsequently shorter glow plug life and more highway driving means longer life since the plugs are not used after start up (or shortly after for afterglow systems)

In my driving environment plugs seem to last for approximately 5-6 years or around 100K miles. Like a previous poster I replace them all when one fails and I've had the best service life from Beru brand plugs and the least luck with Monarck (or was it Monarch?, can't remember) and Champion brand plugs.

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98 Dodge-Cummins pickup (137K)
13 GLK250 (157k)
06 E320CDI (341K)
16 C300 (89K)
82 300GD Gelaendewagen (54K)