Bad Spark Plug? Denso Iridium

[Titius Justus]

I observed an intermittent misfire coming home last night. When I got home I left the engine running and popped the hood. I also had a loud tick coming from the engine. I left the engine running and removed the plastic cover; I isolated the noise to #3 cylinder area, so I unplugged the coil pack and removed it. When I looked down in the hole, the ceramic portion of the spark plug was wobbling every time the piston came up. I shut the engine off and removed the spark plug. It seems the steel crimp that holds the ceramic/electrode in place has come loose. The plugs were Denso Iridium. They have about 5k miles and 3 months of use.

I had the old Bosch spark plugs from the old engine so I swapped that plug out. Fresh anti-sieze on the threads, dielectric grease in the coil boot, and sent it home with about 200 ft./lbs. of torque .

Has anyone ever seen a spark plug do this before? It's a first for me.

Should I pull the rest of the Denso plugs out and replace them with the Bosch type plugs? (They had two prongs protruding from the base to the electrode.)

[aalpine1]

I used the NGK 2288 for years without any issues.

[cwilliamhicks]

Haven't heard about that, but good to know your experience! I used Bosch platinum +4's last time and I can't remember the torque, but I haven't had problems.

What's the verdict on anti-sieze on the threads? I was under the impression that could get cooked and cause problems.

[cochise325]

I hope you are exaggerating that you used 200 foot-pounds of torque to tighten a spark plug in an aluminum head.

[Titius Justus]

cochise325, that was a joke. :-P I said that for 2 reasons. One, to keep the mood light. Two, to see who's paying attention. ;-)

cwilliamhicks, I've never had a problem with anti-sieze. I've used it for years. I use the gray permatex stuff. The purpose of it is to eliminate frozen threads, and ensure the fastening threads will move when attempting to remove it in the future. I think it's particularly important to use when sending plugs into an aluminum head because the threads can easily be damaged if not careful. Also, aluminium has a tendency to "bond" with other metals of fasteners over time, usually because of corrosion. You might find differing opinions on this topic, but I always have and always will use anti-sieze on my spark plugs. I've never experienced it cooking or causing problems, even on exhaust manifold fasteners and couplings.

[cochise325]

cochise325, that was a joke. :-P I said that for 2 reasons. One, to keep the mood light. Two, to see who's paying attention. ;-)

Well you got my attention.

[S61Dan]

I think I have Denso Iridiums in there. About the same length of time as you, no problems so far :

[djb2]

New spark plugs have a plating designed to avoid seizing in aluminum heads. There are specific instructions not to use anti-seize.

I don't know if that applies to reinstalling used plugs.

[Titius Justus]

djb2, that's interesting... I'll have to check the package to see if it says whether or not to use anti-sieze. When I pulled the plug out, the compound was still soft and I could easily wipe it out of the threads.

[ross1]

It happens. I've heard of them blowing the insulator clean out of the plug.

[priler]

I good idea is,right before the last turn or two,right before you're about to take the plug off,is to use compressed air and blow around the plug to remove anything that can fall in.

I hope there's nothing wrong with these Denso substitutes,there doesn't seem to be any other iridium ones. since the original has a resistor,i was planning to use them next time. I've never seen iridium plugs without a resistor,at least not for any car I've owned.


is there another?,iridium one I mean.

[mrgraybeard]

It happens. I've heard of them blowing the insulator clean out of the plug.

I had NGKs in a Mazda V6. A spark plug failed and allowed combustion gases to escape with enough force that it blew the spark plug boot off of the plug! It happened three or four times before I figured out what was going on.

[ross1]

I had NGKs in a Mazda V6. A spark plug failed and allowed combustion gases to escape with enough force that it blew the spark plug boot off of the plug! It happened three or four times before I figured out what was going on.

It's those sort of head scratchers that give us the grey hair.