Spark plug thread issues in your 2013 Ford Expedition at 200,000 miles may result from cumulative wear from multiple plug changes, improper installation, or corrosion. Ford's modular V8 engines have a history of thread concerns that proper technique helps prevent.
Ford Spark Plug Thread History
Early Ford modular engines had insufficient thread engagement, causing plug ejection. By 2013, Ford had addressed the original design issue, but thread wear from improper service can still cause problems. Aluminum cylinder heads are softer than steel plugs, making proper torque critical.
What Causes Thread Damage
Over-torquing strips threads in the soft aluminum head. Cross-threading damages thread starts. Corrosion between steel plug and aluminum head causes galling during removal. Using air tools to install plugs almost guarantees over-torque. Each plug change without anti-seize increases removal difficulty.
Signs of Thread Problems
Plug feels loose even when torqued. Exhaust tick indicating plug isn't sealing. Difficulty threading plugs during installation. Plugs back out during operation. Metal shavings present during plug removal.
Repair Options
Thread repair inserts (Time-Sert is preferred for this application) install new threads without head removal - $400-700 per cylinder. HeliCoil is less robust but cheaper. Severe damage may require head removal for machine shop repair. Prevention through proper technique is far cheaper than repair.