U.S. Department of Energy guidelines state that it takes between 3,000 to 5,000 miles of driving to break in a new engine and reach the optimal fuel economy.
The slightest variation in assembling a new car can impact the estimated fuel mileage and a few drivers will notice a marked deviation from EPA estimates.
The U.S. Environmental Protection Agency (EPA) and the Department of Transportation are proposing different fuel economy labels for new cars. One suggested label uses a letter grade with an A+ going to electric vehicles. The other suggested label uses horizontal bars to compare mileage to other cars, the environmental impact of carbon emissions and a slider bar to depict cost of fuel rather than fuel savings.
The EPA determines fuel economy using cars with 5,000 miles to allow for the break-in period. The EPA says fuel economy typically improves in the first few years of ownership and will retain it's optimum gas mileage if properly maintained.
