This is for a different motor, but because it is a general question, I'm hoping someone here can answer it.

I recently purchased a 1985 Ford Ranger 2.3L Turbo Diesel, and am getting it back into running condition. One of the things that I changed was the glow plugs. It starts right up now, but I would like clarification on glow plug seating.


When comparing the old glow plugs to the new, the heating element on the new ones is about 1/4" longer than on the ones I removed. They are the same part, so I'm guessing this is normal degradation. When I installed the new ones, there was resistance at a depth that left more of the plug outside the block than the old plugs left.

Do the glow plugs slowly degrade over time, and need to be seated a little further into the block as they degrade?

Should the plugs be seated at a depth where they are making contact and have resistance, or should I back them out a little when I feel the resistance? If so, how much? What is it inside the block that the plugs are coming into contact with to create the resistance I'm feeling?

 

If you look at the glow plugs closely you'll find they seal at the junction of the threaded barrel and the actual glow plug tube. The resistance you're feeling may just be the tips of the old plugs which have burned away and lodged in the head. That being the case you may have problems! Examine the old plugs and make sure they still have a rounded end. If they do then the resistance you're feeling may just be carbon buildup. Try and determine the root cause of the problem and go from there. The glow plugs have to be seated properly. It is not uncommon for the tips to swell and break off in the head when you try to remove them. I'm not sure on your engine, but the old 6.9 had a precombustion chamber in the head. The broken pieces could be pushed on into the head and then removed by taking an injector out and getting the glow plug piece out through the injector hole. Hope this helps.

 

None of the plugs had rounded heads, all looked as though they were either broken, or burned off. From what you have said, I would imagine that the resistance I am feeling is the remaining pieces of the old plugs still in the block. I will pull the injectors and see what I can find. Thanks for your insight.

 

Here's what 7.3L glowplugs look like, including one that broke the normal way (upper housing broke off, but tip stayed stuck to electrode, so it was removable with some penetrating oil and vise-grips). If the electrode came out of the tip, then you definitely have a fishing expedition ahead of you.

http://www.backglass.org/duncan/f250..._glowplugs.jpg

Duncan

 

I really have no evidence that mine broke off. Do the electrodes erode over time? That's what looks like happened to mine. The ones I removed all look the same; they appear to not be what they were when they were new, but are very uniform. I had no trouble inserting the new plugs and threading them in, they just don't seat as far as the old ones because the tip is longer (and rounded). And they work fine too. I'll try to get some pictures of the old plugs up today for a reference.