Luggage racks increase vehicle drag, and too much weight in the trunk can cut your mileage. On the average, each 100 pounds of needless weight will cost up to one-half mile per gallon.
Don't 'top off' at the pump. Spilled gasoline adds to air pollution and wastes money. A vehicle topped off may expel gasoline on a hot day before it has been driven far enough to lower the fuel level.
Using a vehicle's air conditioner on a hot summer day could decrease mileage by as much as 21 percent. If it's cool enough, use the flow-through ventilation on your car instead of the air conditioner.
If you're driving on the freeway, keep your windows rolled up. Opening a window creates wind drag and will lower your mileage. Use the car's flow-through ventilation.
The choice you make in engine oil can also affect fuel economy. Your owner's manual will recommend the type of oil to use under specific conditions. When you change your oil, ensure all used oil is recycled properly.
Most cars will run fine on regular, and by using regular unleaded instead of mid-grade or premium unleaded you can save money. So, check your vehicle's owner manual to find out what's right for your car.