Testing and changing the glow plugs on a TD5

So for the past four years or so my Defender hasn't had to start in anything less than around 15c. Now it's back in the UK and when I went to start it in about 8c it took noticeably longer to get going and it was all a bit rocky until it warmed up. I have a couple of brand new glow plugs so I figured I'd like to take a look under the bonnet and find two bad ones to replace.

I've never bothered messing with them before but I was watching this Britannica Restorations video (link) where it says I can simply touch the end on a 12v positive and look for a spark. To save me taking all the plugs out can I simply pop the connectors off and attach a crocodile clip then brush the other end of the cable to a 12v positive from the battery, leaving the glow plug to ground via the cylinder head as normal?

I only ask because I need the car on Friday and I don't have much time to do this job. Cheers.

Here's a thread from last year which is full of info.
There is a lot more, try using the 'search' function for TD5 starting or TD5 glow plugs.


You can test them but to do so properly you need a digital multi meter (DMM) that measures amps.
A good plug draws around 14Amps a bad one much less/nothing.
Using the same DMM you can also measure the resistance this should be between 1 and 2 Ohms, much less and the plug needs changing.

To measure the plugs they need to not be connected to the loom/each other.
The general consensus is that the TD5 really doesn't need glow plugs to start smoothly in the (typical) UK temperatures and that if you have poor starting is is likely something else.

PS, I don't have a TD5 but I see a lot of comment.

Thanks. I'd also read that TD5s are good at starting cold but I'd also read other people saying that's not true. I ended up check all my plugs and they weren't as hard to remove as I thought they'd be. I went through them all and found I only had one working properly so I'll try it again when I can find my torque wrench and get them done up properly. I found I actually had 3 new plugs so hopefully I'm all set now.

Twinnie said:

Thanks. I'd also read that TD5s are good at starting cold but I'd also read other people saying that's not true. I ended up check all my plugs and they weren't as hard to remove as I thought they'd be. I went through them all and found I only had one working properly so I'll try it again when I can find my torque wrench and get them done up properly. I found I actually had 3 new plugs so hopefully I'm all set now.

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I've had a TD5 Disco for 10 years, I hardly ever wait to start it until the glowplug light goes out. I don't live in the coldest part of the country. But I still doubt it is all of your problem. Sadly.