The problem is usually when the plug stays in there a long time, with a bit of moisture, the iron and aluminum interact. That and the expansion and contraction (thermal cycling) eventually lead to a loose plug. After that, it's just a matter of time before it comes flying out.

I've been working with aluminum heads in motorcycles and British 4-cylinders, and now for the last 9 years, 4.6L modulars. They all exhibit the same problems. The iron in the plug and the aluminum in the head interact and eventually they come loose. No way an iron plug and aluminum head are going to stay "friendly" to each other after 100K miles.

One thing about the 2002-2004 dates for the heads. The V10 has the same problems with plug blowout, and they run from 2000-2004, no changes. I don't think the 5.4L's 2002 head change was because of spark plug threads, it was because of the tendency to leak OIL out the back/sides... But I have no real information about that.

Which is really my point, NO ONE can give me a straight answer as to whether the heads were updated to correct this. All YOU can do is say "the spark plugs are different, which means they updated the head" which is not really a valid way to tell. An updated Ford part # retroactive to 2000 would help.

I'm at 21K right now with my V10, and I have removed a COP or two here and there to check on the environmental conditions down there. Next weekend I will be changing the plugs and boots and doing the anti-sieze and torque.

I changed the plugs in my '96 4.6L t-bird at 20K miles, and more than one plug was starting to rust pretty good. From what I saw, and my 20+years of experience as a shade-tree mechanic, those plugs would have come out if I left them in for 50K miles, maybe even less. They were already much looser than the other plugs.

No biggee... keep your plugs in there forever, and let me know when you launch one I'll let you know if I launch one... Deal?

art k.