Possible Causes

WARNING: This page does not describe the selected car, but rather 9 other vehicles, including the 2003 Ford RV Cutaway, 2003 Ford Pickup, 2003 Ford F550 Super Duty, 2003 Ford F450 Super Duty, and 2003 Ford Excursion. However, it is still accessible from the selected car via links, so may be relevant.

Loss of lube oil pressure.
Oil level low; oil leak, oil consumption or incorrect servicing.
Oil level high; incorrect servicing, fuel dilution from tandem fuel pump or fuel dilution from injector "O" rings.
Oil contamination with coolant; oil cooler, head gasket or porosity.
Low reservoir level; engine built dry (not pressure lubed), prolonged period of not running or excessive cranking without starting.