The original glow plugs fitted to a 2.25 Diesel engine had a corkscrew type of element and were wired in series. This meant that if one of the plugs failed then none of the others would work either. Not very convenient on a cold winters morning as it would then be near impossible to start the engine. More modern cars have their glow plugs wired in parallel which meant that even with a faulty glow plug the others would still work. This would give you an early warning as the engine may not fire up as readily as it normally did but wouldn’t leave you stranded. Many owners have converted from the original type of glow plug for more reliable starting and although I never had a problem with the engine not starting, I did experience a glow plug burning out and the element dropping into the cylinder. The hope is that the newer type of plug which has a probe type of element is less likely to suffer from bits falling off.
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The photo shows the difference between the newer probe type element on the left compared to the older cork screw type shown on the right. You can see the older type also has a thick insulating washer (arrowed) whereas the newer one doesn’t. This insulating washer will be visible when the plug is fitted so identification is straight forward.
The new glow plugs come as part of a kit which includes the necessary wiring and fitting instructions. Although not normally needed when converting plug types, I decided to renew the ballast resistor at the same time as I suspected this was the reason why one of the plugs burnt out. There is a bit of a disagreement on forums and websites regarding whether the ballast resistor is required with the new plugs or not. The instructions that came with the new kit says it IS needed so I shall be including it. First thing to do is to remove the old glow plugs and the old wiring that runs from the ballast resistor right through to number 1 glow plug.
Because the new plugs are wired in parallel and therefore earth through their threads the old glow plug earth lead from number 1 glow plug to the engine block is no longer required and therefore needs removing. I fitted my new glow plugs after applying a small smear of copper slip to the threads to help future removal. Then starting from the ballast resistor I connected the wires as per the instructions which state that the wire from the ballast resistor goes to number 3 glow plug and then the other wires are used to connect the other plugs to each other making sure the securing nuts are nice and tight. Then its just a matter of starting the engine as usual.
This photo shows the older type of glow plug fitted to the head. Note that the head isn’t fitted to the block, I took it off to remove the piece of element that burnt off from the old style plug and dropped into the cylinder !
GLOW PLUG KIT (PART NUMBER DA1057)
If you need to test your glow plugs take a test lamp or continuity tester on your multi meter and touch the areas as shown above. If the plug is duff then there will be no continuity, if the lamp lights or multi meter buzzes then all should be well.
CORK SCREW STYLE