* Driving conditions: City driving will yield significantly lower MPG than highway driving. Terrain (hills, mountains) also heavily impacts fuel economy.
* Vehicle condition: Proper maintenance (including tire pressure, engine tune-up, and proper functioning of all systems) greatly affects MPG.
* Load: The weight carried in the truck will drastically impact fuel economy. An empty truck will get much better MPG than one heavily loaded.
* Driving style: Aggressive acceleration and braking will reduce MPG.
Given these variables, it's impossible to give a precise MPG figure. However, a reasonable *estimate* for a 1992 F350 7.3L naturally aspirated diesel would be in the range of 10-15 MPG. This is a broad range, and you could see figures outside of this range depending on the factors listed above. Expect the lower end of that range (closer to 10 MPG) in city driving or with a heavy load.
