* Driving conditions: City driving will yield significantly lower MPG than highway driving. Terrain (hills, mountains) also greatly impacts fuel economy.
* Vehicle condition: Properly maintained vehicles (tune-up, tire pressure, etc.) will get better gas mileage.
* Driving style: Aggressive acceleration and braking drastically reduce fuel economy.
* Load: Towing or carrying heavy cargo will significantly lower MPG.
Given these variables, it's impossible to give a precise number. However, you can expect 8-12 MPG as a *very rough estimate*. It's more likely to be on the lower end of that range in typical mixed driving conditions. You might see slightly better fuel economy on the highway with a light load and conservative driving.
To get a better idea of the fuel economy for a specific vehicle, you'd need to either:
* Check the owner's manual: If you have it, the manual might provide EPA estimated fuel economy figures. Keep in mind these are ideal conditions and likely to be better than real-world results.
* Use a fuel log: Keep track of your fuel-ups (gallons purchased and miles driven) over several tanks to calculate your actual MPG.
Remember, a 1990 truck of this size is not known for its fuel efficiency.
