Your Guide to Understanding MPG

Finding the MPG

When shopping at the dealer, locating the EPA estimated MPG is a relatively straight forward process. All new cars and many used cars have their fuel efficiency rating listed right alongside the window sticker price. These fuel economy numbers are broken into three parts:

• City MPG: The EPA estimate of gas consumption under city driving conditions
• Highway MPG: The EPA estimate of a gas consumption under highway driving conditions
• Combined MPG: The fuel performance for the vehicle when the City and Highway MPG are combined. This is an average of the two separate tests, and it is weighted by the distance covered.

Even if you are buying a used car and the vehicle’s MPG is not directly listed on the sticker price, finding this information is a relatively straight forward process.  By law, automakers must post the EPA certified fuel-economy ratings for all their vehicles. The only exceptions to this are vehicles with a gross-vehicle-weight rating over 8,500 pounds. You can find information on a specific vehicle’s MPG by contacting the car manufacturer or visiting their website. Fuel Economy dot-Gov also provides a listing for all EPA estimates.

EPA vs. Real World MPG

The problem, however, is that EPA estimates are not always the best indicator of a vehicle’s fuel efficiency when exposed to real-world driving conditions. While they are great for comparing one brand new vehicle against another, these estimates can be misleading when used to compare two used vehicles. The reason for this is the conditions in which the tests are completed. EPA fuel economy tests are conducted under ideal conditions, with vehicles that have been properly broken in and that are in top mechanical shape. In addition, these vehicles are tested without a full complement of passengers or cargo and are driven without the air conditioning and other electrical accessories in use. So, if you are buying a used car, these estimates may be grossly misleading. Depending on your driving habits and the condition of the car, the actual miles per gallon can be much lower.

Other Elements Contributing to Fuel Efficiency

While EPA estimates are great for comparing new cars, they should not be your only consideration in a used car purchase. Other elements you can use to determine the fuel economy on a used car include:

• Manual Transmission: Cars with manual transmissions often get better MPG when compared to their automatic transmission counterparts.
• Engine Size: More horsepower and larger engine liter size can contribute to lower MPG. For example, a 1.2-liter engine may have better fuel efficiency than a 1.5-liter engine.
• Clean Diesel: Many newer model cars are being offered with a clean diesel option. This can result in better fuel economy when compared to a gasoline engine.