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Head Degrading Around Coil - Multiple Coil Failure?

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Old 07-12-2018, 11:03 AM
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Default Head Degrading Around Coil - Multiple Coil Failure?

2007 V6 with 90,000 miles. A few weeks ago a shop (not me) put in new plugs. Later coil #5 went out and I replaced all coils. This week coil #5 fails again and this time I notice problems with the metal around the coil collar - see photo.

What is happening here and is it related to the

coil failures?
 
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Old 07-12-2018, 08:12 PM
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It's the cam-cover, not the head.

https://www.jaguarforums.com/forum/s...e-x300-167613/
 
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Old 07-13-2018, 12:58 AM
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Originally Posted by aholbro1 View Post
Right, easy slip. But IS IT RELATED to the coils failing?
 
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Old 07-14-2018, 08:25 AM
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Probably. On the one hand, Magnesium alloys, given their way, would choose corrosion over sexual activity! The localized destruction shown in your photos (and mine) tend to make one think electrical discharge is also involved, however. So perhaps your number 5 coil was firing to the cam cover as well as, if not in lieu of, the spark plug. Can't really fathom how that happened to mine out at the mounting boss, where I have similar damage.

Certainly, given your timeline, the coil was at-work, unless you've been careless with the language:

"A few weeks ago, plugs replaced. Later, all coils replaced...This week, #5 coil fail ...replaced and THIS TIME..."

"A few weeks" - I interpret as a minimum of 3, but possibly more - figuring most people would say "A couple.." if they meant two, though I allow two weeks as a valid interpretation of "A few." However, if more than 4, I'd expect to hear, "About/Over a month ago" depending whether 4/ or more, but less than 8.

"Later" - less exact, but the context indicates a maximum two weeks if the 3 week assumption above is correct. Probably a week or more as otherwise I'd expect "on the drive home.." or "within 5 days, coils failed" or some such.

"Last week" #5 failed again..."THIS TIME" is key because it infers none of the damage shown in your photo was evident when you changed all the coils. So a key unknown here, is how much time/how many miles elapsed between renewing all coils and the 2nd failure of #5? It strains credibility to believe all that happened within the span of a week or two.

Or is it possible the #5 plug well was similarly corroded and you (or whoever changed the coils the first time) failed to take notice?
 
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Old 07-14-2018, 08:38 AM
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You can fit a used cam cover to correct the corrosion problem:

https://www.ebay.com/itm/2003-04-05-...LH_TitleDesc=0
 
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Old 07-14-2018, 10:13 AM
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Originally Posted by aholbro1 View Post
Magnesium alloys, given their way, would choose corrosion over sexual activity!
A very apt description of magnesium. Quite the opposite of the mollusc, if you ask me. (Bonus points if you know that obscure reference)



Originally Posted by aholbro1 View Post
The localized destruction shown in your photos (and mine) tend to make one think electrical discharge is also involved, however. So perhaps your number 5 coil was firing to the cam cover as well as, if not in lieu of, the spark plug. Can't really fathom how that happened to mine out at the mounting boss, where I have similar damage.
Look at it this way. The cam cover sits on a rubber gasket. The mounting bolts pass through rubber bushings. The cam cover itself isn't grounded to the rest of the engine, unless there's a ground strap or similar that I'm forgetting. Let's say your coil's insulation was breaking down, and some juice was discharging towards the cam cover. Now the cam cover has been "charged", so to speak, but where do those electrons go? They will look for any ground they can find, those little-two timing trollops. It's very likely those little harlots were bridging the rubber bushings at the mounting bosses, and traveling through the bolts to the cylinder head and ground. If the bushings had any oil or other contamination, they become semi-conductive and make the flow of current easier.
 
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Old 07-14-2018, 09:47 PM
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That makes sense as far as it goes, Karl....but then I'd have to have discriminating two-timing trollops, I'd think? See? Look at the destruction around all three plug-wells.....a flood of the ho's going over the wall there, why would a few discriminating ones venture all the way out to a mounting boss? All-of-a-sudden the plug wells got religion and quit offering ground so freely?

NBCat, although they're a bit tougher to pull than the X300's, they can be had at the pick-n-pull for $17.95 ($14.95 if you take an old one in for a core) The one shown in your link appears to have a hole in the corner of the rectangle traced by the plug-well gasket, though I may be mistaken. I'd be careful with that one.
 
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Old 07-15-2018, 12:26 AM
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Originally Posted by aholbro1 View Post
That makes sense as far as it goes, Karl....but then I'd have to have discriminating two-timing trollops, I'd think? See? Look at the destruction around all three plug-wells.....a flood of the ho's going over the wall there, why would a few discriminating ones venture all the way out to a mounting boss? All-of-a-sudden the plug wells got religion and quit offering ground so freely?
Close, but no cigar. This inadvertent path to ground always involved two jumps, in series. The first is from the coil into the entire cam cover. The whole cover is charged, still looking for a path to ground. The second jump is through the point of least resistance, the mounting bolts in this case. Once this stray path gets established, you've got two jumps happening simultaneously.

Doesn't make any sense, does it? How can that first jump occur if the second hasn't happened yet? Compare the cam cover to the spark plug wires in an old ignition system with a distributor. With an old system like that, the spark leaves the coil and passes through the cap's center post and then to the rotor. That's a totally solid path so far, with no gaps to jump. Now think about each individual plug wire. A plug wire isn't grounded at all. It's still insulated from ground by the plug gap at the other end. How does the spark jump the first gap (inside the distributor cap) if the second gap has yet to be bridged?

It's kinda hard to explain, but it's basically the originating charge influences the adjacent conductors (plug wire or cam cover) and builds up a charge there, too. It's like sending out feelers, looking everywhere for a weak spot back to ground. The actual current flow is miniscule, it's just building up pressure. Once this secondary charge builds up high enough to jump the second gap, a chain reaction takes place and both gaps get bridged at the same time and lots of current will flow. Thus your promiscuous electrons burn the cam cover at the plug wells and mount bolts at the same time. If either of those two gaps had significantly higher resistance, that would have broken the chain.
 
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