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How long should glow plugs last in a typical diesel engine? And what might cause them to fail early?

I ask because my 20 year-old Ford Courier (an Australian rebadging of the Mazda B-series) needs a new set after I replaced them less than three years ago. (It looks like one out of the four is still good, but I'll replace all four at once)

In comparison everyone else seems to talk as if they last a lot longer than that.

It's not a big deal to replace the glow plugs themselves, but I'm worried that this might be a symptom of a more serious problem.

Edit To Answer Some Comments:

I thought there might be a problem because my car was barely starting on cold mornings (it's Winter here in Australia) even with a fairly new battery (which may be related, my old battery was getting a little tired, and I replaced it a couple of months ago), and was blowing a lot of smoke, which was the symptoms I had last time, and fixed with a set of new glow plugs.

I checked all four still in the car by checking their resistance with my multimeter, one measured 1.5 Ohms, all the others where way over (one looked to be around 300-400 while the others where even higher).

I pulled the "good" one and one of the "bad" ones out and tested them more directly by connecting a jumper lead to the body of the glow plug and the positive terminal on the battery and touching the end of the glow plug to the negative terminal of the battery for five to ten seconds. Only the "good" one heated up. (The other one was cool enough to touch after removing it from the battery)

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  • Do you have a picture of the failed ones?
    – Martin
    Jul 11, 2019 at 11:28
  • Why are you replacing them? Did you get a code of some kind, or were you advised to by a mechanic? A bit more background on the problem would be useful.
    – GdD
    Jul 11, 2019 at 13:09
  • Do you mind me asking what are the symptoms which you're hoping replacing the glow-plugs will rectify?
    – Steve Matthews
    Jul 11, 2019 at 15:58
  • @Martin, I don't have a picture at the moment, but I'll try to remember to take one when I put the new ones in.
    – TimP
    Jul 12, 2019 at 7:26
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    Just to point out that you can test them by measuring the resistance - less chance of getting burnt by a hot one...
    – Solar Mike
    Jul 12, 2019 at 7:58

1 Answer 1

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Your testing methodology seems pretty sound, the plugs definitely sound like they're shot. As you correctly say glow plugs should last a very long time, 3 years is just too short so I suspect one of two things, fortunately they are both simple and cheap:

  1. Faulty/mis-manufactured plugs: if you got a bad set of plugs they may burn out after way too soon a time
  2. Open glow plug relay/control module: The plugs are only supposed to come on when you start the engine and shut off after it's running, if the relay/control module has broken it may keep the plugs on all the time, causing them to burn out much sooner. It wouldn't take 3 years for that to happen though, most likely a few days or weeks, so it's likely this only broke recently

So I'd suggest you replace all 4 plugs and the glow plug relay (or timer, control module, whatever it's called on this model) at the same time. It may be in the manual somewhere, otherwise google is your friend. If you get through the next few months without it failing again you have most likely solved the issue.

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  • The relay sometimes clicks audibly when the glow-plugs turn off, perhaps that was an indication that it was/is getting tired?
    – TimP
    Jul 13, 2019 at 10:37
  • If you can hear a relay it's generally a bad sign @TimP
    – GdD
    Jul 13, 2019 at 16:28

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