Oil in Spark Plug Threads

[Daryl333]

2017 Mustang GT
20,000 miles, Whipple
Gen 3, 9lbs boost.
Like it says I have Oil in every one of the Spark Plug Threads. Plugs have only been in for approx 75 miles. 2 half WOT dyno pulls. Have been getting a Misfire only at WOT.
Which from the crack in the last Plug on the right is the reason for that misfire.
I've read that bad Plug seals can cause this oil on the threads? I got a shop to install Plugs because I'm unable to due to a back operation. Car isn't that old so bad seals going out naturally is strange, no? I figure the cracked Plug was most likely done at installation.
What I'm wondering could this damage to seals(?) or whatever is causing the Oil seepage have been caused by tech abuse during installation of Plugs? I've seen the flunky who did the install.
Thx for any help here.

Oh, great pics of a cracked Plug that (hopefully) was causing a misfire at WOT for anybody interested in knowing what cracked Plug looks like.

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[ice445]

The valve seals are part of the covers, that is pretty odd you're seeing leakage in all 8 holes though. Were the insulators covered in oil too that you wiped off? Or is it only showing up on the threads? If it's the latter, it may just be that the "tech" oiled the threads to make them go in easier or something similarly stupid.

 

[Daryl333]

The valve seals are part of the covers, that is pretty odd you're seeing leakage in all 8 holes though. Were the insulators covered in oil too that you wiped off? Or is it only showing up on the threads? If it's the latter, it may just be that the "tech" oiled the threads to make them go in easier or something similarly stupid.

I got them back exactly the way they look.
I'm kind of sketched out because my car is in good condition for this kind of leak to be happening all on it's own and thought maybe it had some help. Just wanted info before enquiring just what is going on.

 

[ice445]

I got them back exactly the way they look.
I'm kind of sketched out because my car is in good condition for this kind of leak to be happening all on it's own and thought maybe it had some help. Just wanted info before enquiring just what is going on.

If that's how they came out, I think you're good. Just looks like some sort of thread compound they used to make install/uninstall easier. When the tube seals on these engines leak, the entire well will fill with oil, and it will wick through the threads from the top down. On all of these, the oil is in the middle portion and the end and nowhere else.

 

[jacknifetoaswan]

I've had issues with valve cover seals on the #8 (driver's rear) plug for like six years on my GT. The dealer did the TSB to drill the additional holes in the composite valve covers, which then leaked, so they replaced the valve cover gaskets, which then leaked, so they replaced the plug seals and reseated the #8 plug well tube, which then leaked.

So I replaced the valve covers with the aluminum GT500 covers. I've only put about 100 miles on the car since doing it, but I haven't found a leak at this time (fingers crossed).

Might be worth it to replace the valve covers with the updated GT500 covers, as the windage tray in the cover was updated to not dump oil towards the rear of the head.

JR

 

[Sig556]

There are so many butchers out there today. It's really hard to find someone that takes pride in their work anymore. The time of the quality mechanic has sailed. Too many people spend more time on their phone and shooting the shit than actually doing quality work. I have been around cars my entire life and I do as much work as possible on my car as I do not trust other people working on my car. I'll be 80 in September and God willing I'll continue.

 

[OLdchuck]

Ed, I second your sentiment. I am 76 and been around cars most of my life and you are correct that it does not look good for the future of the enthusiast. Hopefully we can continue to do as much of our own work as possible. Glad to see you are still enjoying life.

 

[SheepDog]

If the oil is on the top of the plug, around the porcelain part then it is likely the Valve cover seals. If oil is on the threads then look to poor ring sealing, cracked ring lands (would also run like shit and have a ton of blowby) bad valve guide seals, head gasket issues etc. However, like others have said, it is likely some kind of lube that some dipshit used to thread the plugs in, because having the aforementioned issues on all 8 cylinders at the same time is very unlikely. Get new plugs, and recheck after a few drive cycles

 

[Angrey]

Could be a number of usual culprits.

Either you're getting blowby because you have low compression or the rings aren't fully seated. Or you have good compression but excessive crank case pressure causing more blowby or the valve seals are leaking oil into the chamber, or as others have point out your valve cover seals are bad you'll see it on top of the plug instead of migrating up the plug from the tip end.

I agree with others, that you'd be getting equal leakage across all 8 cylinders if it was bad blowby (for either reason). However, bad valve seals (or worn) would leak equally and if you have bad valve gaskets it might leak equally. The fact that it's migrated to the threads means it most likely a valve cover issue. Or as someone else point out, can't imagine why but maybe they applied some sorta oil on the threads for install (which would be no bueno because the resulting torque value on a "wet" or lubricated thread would be MUCH higher than on a dry thread.

 

[Daryl333]

Well I phoned the shop and talked to the owner.
He said the Plugs NGK 6510 came with the lube(?) already on the threads on all 8.
Said he wondered about it but since plugs came from a reputable source and weren't used, installed them anyway. And upon closer inspection the substance doesn't appear to be oil but something a lot thicker and has hardened up substantially. And seeing how uniform the application is I have to think this was done at the factory. I've contacted NGK about this but haven't heard back. Anyhow this is a relief to know I don't have a leak issue.
Anybody ever have Plugs with threads pre coated?
Thx.

 

[Skye]

Anybody ever have Plugs with threads pre coated?

I have not. Double-checking my thoughts on this topic, I found the following...

https://www.driven2automotive.com/blog/why-you-shouldnt-use-copper-grease-when-installing-spark-plugs/#:~:text=NGK does not recommend the,by up to 20 percent!

This article confirms my suspicions. Lubricant will alter the torque tension properties of the thread.

Torque readings are directly affected by the tension on the thread. Lubricating a thread reduces tension. The tensile strength of the thread remains the same. The reduced tension could cause the technician to over-tighten and break the thread/bolt/item.

 

[Daryl333]

The shop is adamant they didn't use anything and installed them right out of the box after gapping. But I have my suspicions of course.
NGK got back to me and said no way these came from the factory with any coating on the Threads.
I sent them the pics and asked if they have any thoughts on what substance would bake into what's on the threads now. I'm going to see if I can find pics of what this grease looks like baked.
Also going for a WOT dyno test on Friday so will ask some hard questions to the owner.
Maybe flunky added something and is bullshitting but owner says no.
Been going to this shop since 2006 and find it hard to believe they'd bullshit me, but who knows nowdays.

 

[Angrey]

Dry torque values are approximately 30% more than wet. So if it's truly something that was pre-doped, it's fortunate they didn't break off, especially when trying to remove them (over time as lube degrades or leeches it can cause a higher static friction trying to remove it).

Totally weird. I'd say that seems fishy (that someone outside the shop added lube to the threads) but what's more concerning is that the shop didn't have the experience/expertise to A) wonder why the threads are doped when every other plug you pull out of a box isn't and B) Recognize that wet torque values are different (maybe they did and adjusted accordingly, we can hope). Hopefully it didn't wreck your threads/tap in the aluminum head.

The good news (I guess) is that if it is true and it's lube that was on there, you don't have to worry about the seals on the valve covers or the other culprits to explain where it came from.

 

[Unas2k5]

Your original motor blew ?
You have a gen 2 with a gen 3 motor? Alluminator ?

 

[Daryl333]

Your original motor blew ?
You have a gen 2 with a gen 3 motor? Alluminator ?

Are you asking me or have the wrong thread maybe?
My engine is a stock Gen 2 with approx 19,500 miles.

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