* Driving conditions: City driving will yield significantly lower MPG than highway driving. Stop-and-go traffic drastically reduces fuel efficiency.
* Vehicle condition: A well-maintained engine and properly inflated tires will get better gas mileage than a neglected one. Things like the air filter, spark plugs, and oxygen sensor all play a role.
* Transmission type: Automatic transmissions generally use slightly more fuel than manuals.
* Payload and towing: Hauling heavy loads or towing will dramatically reduce fuel economy.
* Driver habits: Aggressive acceleration and braking will lower fuel efficiency.
Considering all this, you're unlikely to find a single definitive answer. However, you can expect somewhere in the range of 10-15 MPG combined (city and highway) for a 1999 Dodge Ram 1500 with a 318 engine. Highway driving might push it closer to 18 MPG under ideal conditions, while city driving could easily drop to below 10 MPG.
To get a more precise estimate for a specific vehicle, you should check resources like the EPA's fueleconomy.gov website (though data for older vehicles might be limited). However, expect significant variation from the reported figures.
