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Discussion Starter #1
I've had this problem with two different cars, a 94 tbird and a 96 cougar
both have 4.6's
both are stock
the tbird was after replacing the plugs, so that one may be me.
the cougar...well, that looks a lot like factory plugs....in 2018....at 190k miles (just got the car...)

anyone else have this problem?

time to make 8 inserts, and replace some plugs...
 

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It's very easy to overtighten the plugs on these aluminum heads and the threads can get damaged. It's also been known to happen on FI cars with the 5-thread plug holes (ealier heads). But a common issue... I wouldn't go that far.

I would be surprised if the car with 190k had factory plugs. I removed factory plugs with a gap over .02" more than the .054" spec at ~130k... what kind of gap on them?
 

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Every time I have seen the spark plugs blow out of a 4.6, it has been after someone replaced the plugs and didn’t use anti-seize on the threads.
 

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I've seen this; removing the plugs with the engine hot will do it.

The plugs come out with threads mostly attached.

I read Here not to mess with the plugs unless the engine sat overnight.

Then to use antisieze liberally. The moly stuff.



I've read that If you're going to tune the car for performance, the thread repair kits make the plugs one step hotter; IDK is that's true, but steel vs aluminum, I'd believe it.

People that put huge money into heads either use the fully threaded heads, or put inserts in ALL plugs, to even them out.

I just swap them cold, lol.

If you blew one out, those are your options, pertty much.



The 3v engines suck; the long barrel rusts, and breaks off in the bore.

My boss did that, after me telling him to do it cold.

He didn't have time to deal with that, so the next day he was asking me how to get them out, lol.
 

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I’ve never had the issue personally but I do what grog does, I never take them off hot and I only snug them tight. Many people seem determined to really crank them down and that’s what does them in most of the time, spec is only 11-13 ft/lbs. I don’t use antisieze.

It’s way more common on pickups with the 5.4 for some reason than 4.6 cars.
 

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The 3v ones it doesn’t matter whether it is cold or hot, they just seize in there from galvanic corrosion and carbon buildup. If the plugs were changed regularly, it wouldn’t be an issue, but people leave them in there for over 100k miles, and by then it is too late.
 

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I've never seen this on a MN12, personally, but I've seen it on several trucks and mustangs of our vintage.

I've seen a plug embedded in an f150 hood; I heard that was 6psi of boost, and a 150 shot. :)

The guys (Cute female manager 0:) ) at advanced sometimes calls me, when they run into weird modular stuff.

They give discounts, so it's all good. :)



Ive seen a plug with ALL the threads still IN the plug threads; there's nothing else to do but timserts, and I would pull the head to do one.

If you have the head off, it's $50 or less for a new head at the JY, so... :zdunno:
 

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Discussion Starter #8 (Edited)
given the amount of corrosion, and the...mess where the electrodes should be...
and the Motorcraft name on the plugs...
I'm calling those original, or really close to it.

and from the other...things I'm finding in this Cougar, I think I overpaid.
As for the Tbird...well, it's somewhere North of 400k, and due for a complete overhaul, both suspension and engine, I might post some of my notes around here when I get around to tearing into it.
 
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