[Vwdiesel] glow plugs

Shawn Wright swright at zuiko.sls.bc.ca
Sun Dec 19 23:36:32 EST 2004

> Is it common for all four glow plugs to fail at about the same time? If 
> one or more glow plugs are shot, do the remaining plugs each get more 
> current because they are connected in a paralel circuit?

No, the current should remain roughly the same per plug regardless of # of plugs 

 If this is the 
> case, does the failure of one quickly cause the failure of the rest from 
> over current (overheating)? 

I don't think so.

> Can cycling the glow plugs on especially cold days cause them to fry 
> faster?

I suppose, but I doubt it. 

> Normally, I go to the block heater when the overnight temperature goes 
> below 10 F. Last night, my daughter forgot to plug hers in and the temp 
> went to 4 F this morning. No Start! I got it running this afternoon but 
> later on it would not start again when the temp had improved to around 
> 20F. I jumped it and had plenty of cranking but not even a wimper of 
> firing. When I finally got it home around 8 this evening, I checked the 
> fuse (only a 10 A on an 85 Golf?) and it was fine. I pulled the glow 
> plug from #4 because it is the only easy one to get out and found it 
> failed the ohm meter test for continuity. I'm sure the other three are 
> the same way. I just had all of these  glow plugs out at the end of the 
> Summer and they were all good.
> What would cause all the plugs to fail so quickly?

I just experienced roughly the same thing - 3 of 4 were dead 2 weeks ago after they 
all checked out fine in the summer. Don't assume all of yours are dead though. At 
20F, I'd expect it would start on 3 plugs, but just barely start on 2. Mine took a *lot* of 
cranking to start on 1 plug, and the temp was about 5C (40F). 
I still don't know why 3 of mine failed, and then two more failed a week later. The first 
could be just age, and the second two were also used plugs, so who knows? 
However, I do find it a bit suspicious that the two plugs that failed in a week were also 
in the two cylinders with low compression and valves way out of adjustment. 
Have you done a compression test or checked the valve adjustment lately?

If you're planning to pull all the plugs, I recommend pulling the fuel lines off - makes 
the job a lot easier. I used to disconnect the bus bar from #4, 3 and 1 then test 
continuity on 1,3,4 directly using a gauge, and using the busbar for #2. I find #2 the 
hardest to reach, so I would only remove the nut if I had to. Now, I have each plug 
wired separately to #4, so I can detach & check easily. The wires also allow you to 
loosen the nut, then remove the plug & re-install using the wire as a holder. (no more 
dropped nuts). I used parts of the bus bar crimped to 10ga wire, but eyelet rings 
would also work well. 10 or 12 ga wire is sufficient for the current of one plug.

Shawn Wright
I.T. Manager
Shawnigan Lake School

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