Possible Causes

WARNING: This page is about a different car, the 2003 Ford Pickup, 2003 Ford F550 Super Duty, 2003 Ford F450 Super Duty, 2003 Ford Excursion, and 2003 Ford Cab & Chassis. However, it is still accessible from the selected car via links, so may be relevant.

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.