Gas mileage varies by year and engine size. From personal experience I would say you can expect to average about 10 mpg. They are rated for slightly higher on the highway but dont expect to get any more than 12.
Without knowing the year or model I cannot give you an accurate fuel economy estimate. However there are sites like the one ran by the government that will tell you.
The Ford Excursion has two types of diesel engines the 6.0L and 7.3L and both get relatively the same miles per gallon. Raging from around thirteen to twenty depending.
