2nd cracked spark plug - why?

[kcjaz]

EDIT: the bit about this being the second #6 plug failure is wrong. It was #3 that failed before. see post 20.

So Saturday night while rolling down the highway at 75 mph, the engine start running rough and I could feel a vibration. Scanned codes and got P0306 which is cylinder #6 misfire. I limped to where I was going and then the 20 miles back home on 7 cylinders.

Pulled the coil and plug and the issue was a cracked spark plug. Replaced it and all better now. The weird thing is that this is the second #6 spark plug that I have cracked. Anyone else experienced a cracked spark plug? What would cause a spark plug to crack in service? The last one was a couple years ago and about 25K miles ago.

 

[sdnative]

Factory installed plugs or have they been replaced? Over torqued? Is the crush washer there?

 

[kcjaz]

Factory installed plugs or have they been replaced? Over torqued? Is the crush washer there?

The plugs had been replaced as a set a long time ago and #6 had been replace when it cracked before. Crush washer was there. It was a little hard to remove and I recall the time before (a dealer did it then) the dealer said the plug was stuck then too. Initially they said they were going to have to pull the head off but then they were able to get it loose. Over torque is definitely a possibility.

 

[TLC2013]

Bummer, sorry to hear about your troubles. What were the miles when the plugs were initially replaced and the first time the plug was discovered cracked?
I recently replaced mine at 100k and all eight came out easily. Torqued the new ones down to spec without issue. I wonder if whoever did the initial replacement of the plugs butchered up cylinder 6 and its plug.

 

[04UZJ100]

Bummer, sorry to hear about your troubles. What were the miles when the plugs were initially replaced and the first time the plug was discovered cracked?
I recently replaced mine at 100k and all eight came out easily. Torqued the new ones down to spec without issue. I wonder if whoever did the initial replacement of the plugs butchered up cylinder 6 and its plug.

What sorts of extensions need wobbles did you need? Anything crazy or any tips you can share?

 

[kcjaz]

Bummer, sorry to hear about your troubles. What were the miles when the plugs were initially replaced and the first time the plug was discovered cracked?
I recently replaced mine at 100k and all eight came out easily. Torqued the new ones down to spec without issue. I wonder if whoever did the initial replacement of the plugs butchered up cylinder 6 and its plug.

I had all 8 replaced at 100k. Then #6 cracked at 125k and now again at 155k.

How hard was #8? Were you able to just take the brackets on the hard cooling system tubes off to move them enough or did you have to take some of the hoses off?

 

[TLC2013]

I had one swivel adapter and a few different extensions and the plug socket. I followed the tutorials here on MUD that were posted by a couple members and made quick work of it. Basically the rear plug on the passenger side is a PIA and requires the most attention and work to remove. The others were straightforward.

 

[kcjaz]

What sorts of extensions need wobbles did you need? Anything crazy or any tips you can share?

Nothing crazy. A medium 3/8 extension and one swivel fit in there but I couldn’t break it loose with my 3/8 ratchet. I used my 3/8 18” breaker bar that has a ratcheting swivel head and one extension. Also you need a 5/8” spark plug socket. You going be able to get the plug out of the hole with a regular deep socket.

 

[TLC2013]

I had all 8 replaced at 100k. Then #6 cracked at 125k and now again at 155k.

How hard was #8? Were you able to just take the brackets on the hard cooling system tubes off to move them enough or did you have to take some of the hoses off?

Cylinder 8 was easy only because I followed the super detailed instructions that were posted by a couple members. Essentially it involves removing a few bolts that hold coolant lines that obstruct the coil and run over the valve covers.

 

[bloc]

Watching this thread. Many years of auto forum activity I’ve never heard of this..

 

[molanginaeda]

Any pics of the cracked plug?

 

[kcjaz]

Any pics of the cracked plug?

I have the old plug and can take a pic when I have time later but a pic won't show the crack. The porcelain part spins inside of the lower metal part. Its like someone torqued on the top (porcelain part) while holding the bottom. Not sure how that could happen putting it in or taking it out though unless the socket wasn't seated on the hex head but even so I don't see how that could grip the top part enough to twist and break it. The plug ran for about 25K before failing completely. I suppose it is possible I damaged the plug removing it but it was clearly bad before I touched it as I had the misfire code and all of the physical symptoms of running with 7 or 8 cylinders.

The only thing I can figure is it was a bad but still functioning plug to begin with and just took 25K to fail. I would just except that like I did the first time but twice in the same cylinder?

 

[sdnative]

Could the plug have been cross threaded and damaged the head? If the head is aluminum could the plug have been cross threaded to a fully installed depth? Not sure how possible this would be.

 

[kcjaz]

Could the plug have been cross threaded and damaged the head? If the head is aluminum could the plug have been cross threaded to a fully installed depth? Not sure how possible this would be.

Cross threading could happen but I don’t think so here as after I broke the plug loose, it came out easy and I put the new one in with my fingers for a lot of turn. The head threads seem fine.

 

[kcjaz]

Here’s a pic of the bad plug. You can see discoloration around the bottom of the porcelain. It’s burned.

 

[40Man]

If a cylinder runs lean it can do that. Maybe you have a dirty injector. Haven't seen that on the 200 before.

Could have also been a bad batch of plugs, but I'd guess clogged injector causing detonation. I'd remove the injectors and clean or replace them, or you could run Seafoam through the whole system if you want to start with the less labor intensive option...

That is the optimistic answer.

If your head is cracked, the hot/cool mix could also cause cracking...

 

[molanginaeda]

Denso spark plug? Beware of fake one as the market flooded with lookalike. I never seen a spark plug wear off that bad. Normal iridium plug has life of 100k+.

 

[kcjaz]

Denso spark plug? Beware of fake one as the market flooded with lookalike. I never seen a spark plug wear off that bad. Normal iridium plug has life of 100k+.

plug was Dealer installed. Doesn't mean its not a fake but I doubt it. Please no dealer rant hi-jacks here. I started one of those recently and regret it.

 

[Lester did that]

plug was Dealer installed. Doesn't mean its not a fake but I doubt it. Please no dealer rant hi-jacks here. I started one of those recently and regret it.

Bummer. That plug does look pretty beat up for 25k. Improper torquing is the problem 95% of the time. You have all kinds of issues with heat if over or under torqued. Besides the binding and crushing if over torqued. I would guess it was under torqued from the look of that plug. It was rattling around just enough to crack the porcelain and some gas and oil also leaked out in the process.

I bet because they had a problem with #6 removal the first time and the mechanic was probably young and just figured not to torque it down all the way to avoid the issue in the future. Trying to be a little too smart.

I am not a fan of dealer maintenance but I buy all my parts down to gaskets from the dealer and pay the premium. It's the only way to be 100% sure it's not a knock off part.

Check the #6 ignition coil for damage or a little cleaning

 

[kcjaz]

Update:

So on my way to LCDC, #8 misfired and I replaced the plug and the ignition coil. It was a little nuts and covered in this thread. Being spooked and paranoid, I replaced all spark plugs while in Durango enroute to LCDC. Now that I'm home, I checked my records and well, my memory wasn't correct. I actually have no record that any of the plugs have been replaced except the one that failed and cracked a couple years ago. Above, I said it was #6 and that it was the second failure of #6 at my son's wedding. My paperwork says it was #3 that cracked a few years ago. After pulling them all out, in Durango, all but number 3 were difficult to remove, as in overtorqued or just stuck after being installed for 150K miles. After pulling all of the plugs, they all were pretty nasty and I am now pretty sure that they were all original and had actually never been replaced. Somewhere, I got in my head that I had the plugs replaced at 100K but now I don't think they really were ever replaced.

So, I think the moral of the story is don't go 150K miles on a set of plugs. And if you do, carry spare plugs, a spare ignition coils (or 2), and tools.