Testing Glowplugs

[Yostumpy]

So the saga of my poor starting 300 tdi continues. Fitted all new Ngk glow plug - they were all duff. Got multimeter out to check they were working result 0 v. Poo!!

The dash glow plug light work and there is a relay click. But clearly all is not well. Glow plugs definitely all wired correctly . Is there only the one starter relay far right had relay in cabin disrupt or is there another on thebulkhead??

when I changed mine this afternoon, and it was time to do the last one, ie the one nearest the bulkhead, I noticed that there were 2 wires on this, and when I came to wire it up again, I nearly forgot one of them as it had slipped under the manifold thing, and wat with the air filter being in the way, was difficult to see. I assume yours has 2 wires on this one as well, ?

[cypermethrin]

Hi yes definitely put the two wires on the first glow plug and the rest connected in series

[LandyManLuke]

They're not actually in series, they're in parallel...

[cypermethrin]

Ok in parallel then!!

[rusty_wingnut]

well my two penneth, my 300 started fine and I have no idea if the plugs are working or not.

[Ian Barrett]

Morning all.

After reading this thread I got to thinking about how my 2.5td is taking longer to start. I was up holding the plugs for 30 seconds before starting. I was inspired enough to buy new Bearmach glow plugs which I played with last night.

My old plugs - which from memory were from Land Rover but donkeys years ago - were bench tested against the Bearmach ones using a battery.
The old ones heated up from the middle and after 30 seconds the whole of the last inch of the plug was bright orange.
The Bearmach plugs got yellow hot at the very end of the tip within 10 seconds.

I am optimistic I've improved things with the new plugs., so thanks for the inspiration.

Now to a question for you;
Out of curiosity, I checked the voltage on the newly fitted plugs and found I was getting between 9.6 and 9.8 volts to the plug tops when I turned the key.
Should this be higher?

[javelinadave]

On the 2.5L N/A the book says 11 volts so 9.*v sounds pretty low but I'm not sure about the TD. I think the glow plug specs also call for 11v so it sounds like you are not getting all you can out of them.

Are you testing with all the plugs hooked up or are you just testing the wiring output?

[Ian Barrett]

I was testing on the top of the plugs. They all pretty much measured at the same voltage.

[mmgemini]

So, just to check this, I've put new ones in, and thought I'd check the old ones, so out with the jump leads, on to battery, earth lead clamped around the body, whilst I hold the earth clamp, then pos lead clipped on to the end nut, should it glow in this situtation, coz none of them even got warm! or am I doing it wrong!? i mean 4 out of 4 duff!

Yep you did it the right and only way to check heater plugs. PLEASE though remember to hold the plug with pliers otherwise you'll make your eyes water.

I'm told that the heater plugs still glow for some time after the engine has started.

When I pulled the heater plugs out of my 300Tdi. Not one of the four was working.

[David Sparkes]

...

Now to a question for you;

Out of curiosity, I checked the voltage on the newly fitted plugs and found I was getting between 9.6 and 9.8 volts to the plug tops when I turned the key.

Should this be higher?

Yes, you should investigate where the volt drop is occurring, because if it's in the earth side of the circuit (block to chassis, chassis to battery) it could also affect, in a bad way, the ability of the alternator to keep the battery charged.

HTH

[unclemicky]

Great thread all. Very informative.