* Year of the truck: Engine technology and emissions regulations changed significantly over the years the 351 was produced. Older trucks will generally get much worse gas mileage than newer ones (even if the engine is the same).
* Transmission: Automatic or manual, and the number of gears will impact fuel economy.
* Rear axle ratio: A lower numerical ratio (e.g., 3.50) will result in better highway mileage, while a higher ratio (e.g., 4.10) will provide better acceleration and towing capacity but lower overall fuel economy.
* Vehicle condition: Proper maintenance (tune-up, tire inflation, etc.) significantly impacts fuel efficiency.
* Driving habits: Aggressive driving will dramatically reduce fuel economy. Highway driving generally yields better mileage than city driving.
* Load: Hauling heavy loads drastically reduces fuel economy.
While a modern 351 V8 is unlikely to be found in a newer F250, expect a very low MPG in the range of 8-12 MPG for an older model, particularly with city driving and a load. Highway driving might push it to the upper teens, but only under ideal conditions. This is a rough estimate, and real-world mileage can vary considerably.
