Glow plug problem (keeps blowing up)

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Mandy

Mandy

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Hi guys. The first glow plug (the one nearest the bulkhead) blows as soon as I change it. I’ve now changed it twice (the first time I thought I may have bought a faulty one). Any idea of what could be problem and how to solve it?
 

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They are wired in series, aren't they? Like Christmas tree lights...
I'd guess one (or more) of the others has gone short circuit, and is overloading the others. And the new one just happens to be the weak link in the chain.
If you can, check the resistance of the others individually, and see if one is significantly closer to zero ohms than the others/a known good one.
 
Are they pigtail type, or the later straight jobs?

Iirc pigtails one are something silly like 8 volts? straight ones are 12 volts.
 
Is the resistor in good order, or is it shorting, or is the power lead on wrong terminal, the resistor needs to run in series with the glow plugs
 
It’s the pigtail types. I changed all of them because I had no idea which was the faulty one. You can’t get the wiring wrong because otherwise the cable ends don’t fit. Thanks for the suggestions - I’ll let you know how I get on.
 
TheMegaMan said:
They are wired in series, aren't they? Like Christmas tree lights...
I'd guess one (or more) of the others has gone short circuit, and is overloading the others. And the new one just happens to be the weak link in the chain.
If you can, check the resistance of the others individually, and see if one is significantly closer to zero ohms than the others/a known good one.
Click to expand...
No they're in parallel, it's physically impossible for them to be in series
 
Marmaduke said:
They all share the same live feed but that doesn't mean they are in series
Click to expand...
No, indeed. I understood they each had 2 terminals, with the output of one connected to the input of the next. Having checked again, I see they earth through their body, so clearly they are in parallel. Sorry for the irrelevant and misleading comment.
I'm really curious what it was I saw, now. it was a hand drawn sketch in this site...was showing something like 2v across each element plus a separate resistor. Maybe I imagined it...
 

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Last edited:
Is the ballast resistor needed for the parallel plugs? I have read conflicting opinions on this before.

My 2 1/4 engine had parallel plugs wired to the ballast resistor when I got it. When I rebuilt it, I wired it up again as it was before.

The orange light on the dashboard was still wired up, but only glowed very faintly. It could only be seen in low light conditions. It doesn't seem to light up at all these days.
 
I left the ballast resistor on , the parallel plugs need 12v so the feed for them comes off the 12v side of ballast resistor
Normally the glow plug light is 6v and ok when using the series plugs
Needs to swap for 12v bulb for parallel
The bulb has two leads off it one end goes to 12v heater plug feed other end to earth
Attachéd is my finger drg of how I wired in a relay
 

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If your glow plugs have the coil on the end they are only rated at 2 Volts so are wired in series. The resistor is to drop the voltage from twelve volts to 8Volts.
Modern glow plugs are fed 12V and only have one wire attached and earth through the body.
 
Thanks for the replies.

I changed the parallel plug connection to the 12v side of the resistor. It seemed to start more easily than before, which is not surprising if the 12v plugs were only running on 8v.

The dieselglow drawing that steve2286w posted appears to show the parallel plugs wired up with the resistor still in the circuit.

Also, is there any advantage in connecting the live feed wire to the second from last plug? The older Mitsubishi Shogun 4cyl diesel engine also has the feed wire connected in the same place, so there must be some reason for doing it. The feed wire on my Series engine goes to the last plug at the rear of the engine. That is also how it was when I got it.

I also wired the bulb up as shown and swapped it for a 12v type which now lights up very well. I do wonder if it may be worth running a wire back from the number 1 cylinder plug to feed the bulb. This way you will know if there is a break anywhere in the plug circuit as the bulb will not light up. With it being wired between the ballast resistor feed side and earth, it will still light up even if the wire from the 12v resistor terminal to the plugs is broken.
 
Webley1991 said:
Also, is there any advantage in connecting the live feed wire to the second from last plug?
Click to expand...
I can’t see any real advantage apart from if connected to no 4 then the link wire between 3 and 4 was broke only 4 would work but if on no 3 with same break 3,2 and 1 plugs would work, perhaps it’s shown that way just to demonstrate it does not need to be wired as series plugs
The bulb in the dash just has the two wires to make it work so one end to earth and the other end from a 12v that’s live when the heater plugs are on , so yes you could remove it and put it on No1 plug if wanted and it would show a break in any of the link wires by not lighting up when key turned to heater position
If you have 2 positive feeds to the bulb then if bulb goes out would you know if it’s feed from ignition or feed from no 1 thats faulty
The heater plug leads so heavy unlikely they should break
 
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