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)