In all the years that I have owned diesel engines, I have never had a glow plug go bad, so the answer is no. I have used these extractors to remove broken spark plugs and broken bolts that I had drilled holes into, and most of the time they have worked very well. Occasionally I have had to put some heat on the offending part to break it loose, and for that, I use an oxy/acetylene torch. There is no one way that works for everyone, and a lot of what works best for one person doesn't work for another. You have to have a "feel" for the tool to know when the tool is working, and when it isn't and it is best to stop and try another method. I have seen too many people break an extractor off because they didn't have a feel for when to stop and remove the extractor. I remember breaking off an extractor when I was working on my 1954 Willys, and having to take the front wheel hub off and take it to the machine shop to have the broken extractor extracted along with the broken bolts. While plowing the nuts worked loose and snapped off the studs on the 4-wheel drive hub. I learned a valuable lesson that day, not to be in a hurry, and to know when to stop and ask for help from someone more knowledgeable.