1998 Ford Expedition snsmoke out the tailpipe

White smoke is a sign of burning antifreeze. Suspect a leaking cylinder head gasket. If you want to verify that first, add a small bottle of dark purple dye to the coolant, then check a few days later with a black light. The dye will show up as a bright yellow stain that you can follow back to the source. In this case you'll find it inside the tail pipe.