38 problems related to engine have been reported for the 1998 Ford Expedition. The most recently reported issues are listed below.
While sitting at idle, the engine blew a sparkplug from the cylinder, completely stripping the threads and requiring an entire new header assembly ($1800 repair). I had never heard of such a failure but the dealer has seen it on other Expeditions/navigators and f-150 pickups. This SUV is used as my wife's "Mini van" and does not pull trailers or go off-road. There has to be a manufacturing defect with the aluminum head.
Incident 1 (dated 01/27/00): spark plug blew out of driver-side cyclinder head. Dealer retapped treads, replaced spark plug, reassembled engine ($1216. 79) incident 2 (dated 08/29/02): spark plug blew out of driver-side cyclinder head. Dealer replaced cyclinder head, reassembled engine ($2035. 61).
Vehicle had a cylinder head failure blowing spark plug out of the #4 cylinder causing gas to pump out over engine. Estimated cost to repair by green valley Ford $4100. 00.