* Year of manufacture: Older cars generally have lower MPG than newer ones.
* Make and model: Different manufacturers and models have different designs and technologies affecting fuel economy.
* Engine size and type: Even within 4-cylinder engines, there's variation in displacement (e.g., 1.6L vs. 2.5L) and technology (turbocharged vs. naturally aspirated).
* Transmission type: Automatic transmissions typically have slightly lower MPG than manual transmissions.
* Driving habits: Aggressive driving significantly reduces fuel efficiency.
* Vehicle weight: Heavier cars generally have lower MPG.
* Tire inflation: Properly inflated tires improve fuel economy.
* Aerodynamics: A car's shape impacts its fuel efficiency.
You'll find a much wider range of MPGs for 4-cylinder cars than you would for, say, a specific model year and trim. To find the MPG for a *specific* 4-cylinder car, you should consult the car's owner's manual or resources like the EPA's fueleconomy.gov website (for US vehicles).
