Possible Causes

WARNING: This page is about a different car, the 2008 Ford Pickup, 2008 Ford F550 Super Duty, 2008 Ford F450 Super Duty, and 2008 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, incorrect repair
Oil level high - incorrect repair, fuel dilution
Oil contamination with coolant - oil cooler, head gasket, porosity
Oil contamination with diesel fuel - injector leak, high pressure pump leak