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Broken Spark Plug Prevention

I have read numerous posts and articles on broken spark plugs and the hassle it is to remove them once broken. I have replaced plugs numerous times on several vehicles and never once broke a plug. However I am sure the day will come.

Is it advisable to remove the plugs even before they need replacement to apply anti-seize compound or atleast keep the threads free from corrosion or galling? I figure it would also be a good opportunity to check gap and condition of the plugs.

Or is this a waste of time and potential risk one could break during the PM procedure.

Yes. It is a good idea to at least loosen and retighten sparkplugs on occation. Most people believe that 100,000 mile sparkplugs means that’s how long they should remain in the engine. However, if the plugs are left in the engine that long they can become forever plugs.


If the plugs don’t have a crush washer, and most of them don’t anymore, use a torque wrench to install them. Use nickel-plated plugs if that is what was installed originally. The plating is anti-seize. Use anti-seize if the manual calls for it. Do not use anti-seize if the manual does not call for it. The torque figures will be different for dry and lubricated threads and anti-seize will lubricate the threads. With aluminum heads, work with them cold.

Look at the post from Andrew and his missed 60K plug replacement. Since there is no “big brother” to cover you when a plug becomes stuck due to long service intervals (even if the manufacture says its OK) I go with the PM activity.

You left out important information like how often you change them and what kind of vehicle this is. However, in most cases, following these two steps will ensure there are no additional steps necessary.

  1. Torque the plugs to spec. Use a torque wrench. You will be less likely to strip the threads and they will probably come out just fine as long as you check and replace them on schedule.

  2. Be careful not to cross-thread the new plugs. Carefully hand-tighten them before you use the torque wrench.

How long do you go between plug changes?

I agree with replacing or at least loosening the plugs now and then but if you go to the trouble of removing them for a visual inspection then simply replace them.

Newer vehicles run as lean as possible and especially with platinum or iridium plugs a visual inspection may not reveal a lot. A plug may look fine and misfire anyway.
Plain old copper core plugs are a bit more “readable” if you want to call it that.

Everytime you pull that sparkplug wire off the plug is one more chance to damage the wire.

Probably this is old school and not recommended these days in modern cars but I was always in the habit of taking the dipstick and touching it to the threads of the spark plug for 1 drop of oil more or less before installing them and never had a frozen plug. Please correct me if this a bad thing to do. Many plug wires are prone to problems if treated badly so use a boot puller or treat them gently.

I am not asking for any particular vehicle, for now just a perspective on when I will have to tackle the job. Currently I have a ford escape and honda pilot.

In the past couple years, I changed the plugs on a 99 Jeep GC that had original plugs with 140K miles. There was no signs of worn plugs, misfiring, or poor engine operation. I simply wanted to put new plugs in and moreso see if I could handle the job. The plugs came out fine with no problems. Surpirisingly each plug had equal wear and there was no electrode even in place. This told me I had good enough spark to jump the now enlarged gap.

The problem with this job was getting the coils out. Since the coils were never removed they were stuck in there pretty good. I had to use a means of prying them loose and out…which can be dangerous in the sense that the coils could become damaged. Luckily I didn’t break any coils because I would assume they can get pricey. I did apply a dielectric grease on the boots and o-rings to avoid this in the future.

I always hand-tighten first to ensure I am not cross threading and you are dead on about torque specifications. I am sure the average DIY’er probably overtightens plugs and causes eventual freezing or breaking. I learned from a grandfather and father mechanic that they more or less need to be snug and not too tight. I don’t use a torque wrench and never have had a problem. The next time however I will use a torque wrench to be sure.

Or buy a diesel, no spark plugs to worry about.  :-)

Actually, putting a drop of motor oil on spark plug threads is not a good idea.
It won’t harm anything if the plugs are in and out on regular basis but if left in place for a while the oil can coke and may damage the threads when the plugs are removed.

Basically, coking means cooked oil and this is often the caue of turbocharger failures in which coked oil seizes the impeller shaft.

'98 Mustang Cobra 175k mi. Decided to replace the spark plugs, hood up, engine sitting in the sun. I backed out the old spark plugs but was unable to screw in 2 of the 4 new plugs - the old ones wouldn’t screw in either. In a panic, I went to the car parts store where I bought the plugs and they told me, ‘it happens all the time - you need a “thread chaser” to rethread the engine block holes. However, this might drop metal shavings into the block - it’s better to let a mechanic dismantle the whole engine.’ Instead of suffering the embarrassment, cost of tow, and cost of the mechanic, I decided instead that “a few beers and time to think” was the solution.

After tossing a few back, I went back to the car (now sitting in the shade) and tried the plugs again. This time, plugs #3 & #4 screwed in like butter (the heat of the sun expanded the block and plugs enough so they didn’t screw in).

Here’s where it gets good - now w/job almost done, plug #8 would not go in at all (now night time - engine cold). After more panic - another beer and time to think, i put plug 8 into the freezer and waited 1/2 hr. I pulled the plug out of the freezer, quick ran to the car, and it screwed like butter.

Hope someone will benefit - love your show.

If you ever use a thread chaser put a little grease on it to catch small pieces of metal. Same with a full on tap that you are using to cut threads so you can put in a plug insert

I always use a recommended anti seize on the threads of plugs, esp if they go into an aluminum head (as all do now!). These will seize and cause lots of aggravation on occasion if never properly treated. I would just change to a new plug and replace using antiseize. Make sure you DO NOT adjust the gap on a new Iridium or Platinum plug. If the gap is not right then return it, adjusting the gap will damage the plug, Iridium is harder than Platinum.