Basically, the diesels are workhorse engines that get better fuel mileage and last longer than the gas engines. The 7.3 Powerstroke is one of the best diesels but stay away from the 6.0 Powerstroke; it has many problems. Diesels in general need more maintenance and more expensive maintenance than gassers (the 7.3 takes 15 quarts of oil and 8 gallons of coolant). Early V10's would occasionally blow a spark plug but the later years don't have that problem. In a shuttle bus the V10 will get around 8 mpg and the 7.3 can get 11-12. The E450 has a higher gross vehicle weight rating (GVWR) than the E350. Our GVWR is 14,000 lbs. and our actual weight with tanks full and all our junk loaded is right at 12,000 lbs.
Go to the "Mechanical and Drivetrains > Ford Drivetrain" section of the forum and check out "The care and feeding of the Ford 7.3L Powerstroke" at the top of the list for an idea of the maintenance requirements of the 7.3L.
