Understanding Used Vehicle Fuel Economy

Also known as fuel efficiency, the fuel economy of a used car indicates how far the vehicle can travel using one gallon of gas. The fuel economies of new and used cars are expressed with an MPG, or miles per gallon, rating. MPG ratings are issued by the EPA (Environmental Protection Agency) and are usually the same for new and used vehicles. In some cases, however, the fuel economy of used cars may be somewhat less than that of new vehicles. Read on for an explanation of how used car fuel economy works and why it matters.

City/Highway MPG Ratings

If you look up the EPA's MPG rating for a used vehicle, you will find two numbers-a city-driving rating and a highway-driving rating. The city MPG rating reflects the fuel economy of a vehicle that makes 23 stops over 31 minutes at an average speed of 20 mph and a maximum speed of 56 mph when started with a cold engine. The highway MPG rating, on the other hand, starts with a warm engine, doesn't make any stops, drives ten miles, averages a speed of 48 mph and never exceeds a speed of 60 mph. These numbers are then reduced by a certain percentage to better reflect real-world conditions. As of the 2008 model year, the EPA has added additional tests to determine these MPG ratings.

Differences in Fuel Economy for New and Used Cars

Normally, the fuel economy of a used version of a vehicle is no different from that of a new version. As a result, you should be able to rely on the published EPA fuel economy ratings regardless of whether a vehicle is used or new. These ratings are sometimes too optimistic, but that applies to both used and new cars.

However, certain factors may diminish the MPG rating of a used vehicle. For one, a used vehicle often has worn-down tires that may also be improperly inflated. The condition and inflation of a used car's tires can have a substantial impact on its fuel economy. Moreover, how recently the vehicle has had an oil change and what grade of motor oil is currently in the car will affect gas mileage. The EPA estimates that using the motor oil grade recommended by the manufacturer can improve gas mileage by 1-2 percent. Even small things like how clean the used car is can influence fuel economy. Dirty, unwaxed cars are less aerodynamic and result in more drag, which in turn reduces fuel efficiency.