Include

[akrewat]

Plug blowout IS preventable, you just have to do the maintenance. If you have no idea if the plugs were already done, DO THEM. Being careful to spray penetrating oil (not WD40) in there, loosen them 1/4 turn, spray more, loose another turn or two, blow out the holes (be careful of your eyes), and remove the plugs. Check the plugs for aluminum in the threads, and if there is any, check the threads in the head with an inspection mirror and see if it needs an insert.

Reinstall with anti-seize, torque to specs (14 ft/lbs) and use dielectric grease around the tip of the COP boot, where the boot seals to the COP and where the boot seals to the head. This will keep moisture out and help prevent corrosion between the plug and the head.

Give it a month or so, and RETORQUE the plugs. Every year after, RETORQUE THE PLUGS or remove, clean and reinstall.

The killer is the 100K-mile maintenance interval. This allows so much time to go by the plugs corrode, and iron/aluminum interaction is going to work them loose over time.

The stock plugs were not zinc-plated (galvanized), but the Motorcraft/Autolite replacements are, which also is another cause of the issue.

There were some changes in the factory torque-down procedure around 2000, and then in late in 2002 (model year 2003) they went to long-thread heads. I've still heard of long-thread heads blowing plugs, so it's essential to MAINTAIN the plugs.