I took the car out last week for a ride. I hadn't really driven it much in the last month but it started up just fine.

After a few minutes, I noticed that between 35-45 mph, it seemed to have a little shudder, sort of like a misfire. It almost could have been nothing, and lots of folks wouldn't even notice it. From 50-62 or 63, it smoothed out and ran perfectly. No smoke to speak of and power was good.

Fast forward to later at night, after the car had sat for 3 hours. Pull out the knob, and wait, and wait, and wait. The element in the dash never lights up. No glow! I pull it out further to start, and after 10-12 seconds or so, and a little throttle, it starts up, belches some smoke and runs like normal.

Drive to the ice cream store, sit for an hour, still no glow. Cranks a little longer than normal but starts, and we go home.

Today, I pulled the glow plugs expecting to find a burnt one like last time this happened. No such luck. No carbon build up, as 3 out of 4 of them have less than 1000 miles on them. One burned out very soon after installation, so was replaced by one of the old ones. This arrangement has worked well, and it looks as good as the other 3.

Is it possible that the glow plugs can go bad without obvious visible damage? The wiring hasn't been disturbed and it has been working fine til now.

Loop plugs?

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

Yes, original style loop plugs.

Check for continuity thru each plug. Is there a fuse in the 115 glow system?

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

I'm pretty sure there is not. I'll put them back in and put a light on them thanks.

There must be a fuse.

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

You can check continuity with the plugs out. Put an ohmeter on the two connector points and read thru the loop.

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

There is a strip fuse on your firewall I believe. If it is bad or ever goes bad. There are two fuses out there for this application. Each with different ratings. Get the right one for your setup.

The quickest test for your series system. Get someone to turn the glow plugs on with you either using a 12v test light or a meter. On the glow plug closest to the firewall there should be about ten to twelve volts or the test light should light. That test should indicate where to look for the issue.

I do not now and never have owned a car that uses your setup. I have a later version of the series glow plug system in a 77 though. Your system is kind though in comparison as it does not have the expensive glow plug relay up under the dash. Instead a nice simpler electro mechanical system.

Also sounds like you have a really good engine as it does start with no glow plugs still. Far too many of these engines are getting a little too tired after all these years to do so.

It is kind of stupid but I believe they might use another glow plug as the indicator. If so if it is burnt out the whole system might be down.


If the system is designed as I suspect. It was wasteful to some extent. This to me is just a practical start to finding the glow plug circuit problem.

The sensation or experience you had while driving remember is not related to the glow plugs either.

Does the gorilla knob system use a fuse? I was thinking that what he experieced while driving could be related. If the glow plugs shorted out somehow and put a large draw on the electrical system, it might produce the symptom he described on a low horsepower engine.

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

Possible I suppose. There is no absolute requirement for a fuse in this mechanical/electrical system.


I just sniffed around on the web and returned. . There is no fuse apparently.

73 220D Glow Plug Problems

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84 300D, 82 Volvo 244Gl Diesel

Thanks for the replies, guys. I haven't worked on it any more, but will do the continuity test next time I get out there.

I got the car back together. While it was down I changed the valve seals and checked the compression. Just over 300 across the board. I didn't even look into the glow plugs again, but when I went to start it, they worked. Now it's an intermittent problem. I'm going to check the gorilla knob. When I changed the rheostat for the dash lights I dropped one of the screws down in that area, never to be seen again. I bet I find it, and maybe it's in there mucking up the works.