A 2003 Ford Expedition's owner's manual is the definitive source for recommended oil viscosity. While 5W-50 *might* be acceptable in certain situations (e.g., very high temperatures or modified engines), it's generally
not recommended as a regular replacement for the viscosity specified in your owner's manual. Using a significantly thicker oil than recommended could negatively impact engine performance and longevity.
Before using 5W-50, consult your owner's manual. It will list the appropriate oil viscosity grades for your specific engine under various operating conditions. Using the wrong oil viscosity can cause problems ranging from reduced fuel economy to engine damage.
