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Those Miles Per Gallon Claims May Not Be What They Seem

A newly discovered “MPG Gap” might mean that your car is using a lot more fuel than you were told it would.

Those Miles Per Gallon Claims May Not Be What They Seem
Gas Pump, vistavision via Flickr

The whole point of buying a hybrid car is to save money on fuel, and do the planet a favor. But, according to a new analysis, some of the manufacturers’ claims may not be what they seem.

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Consumer Reports tested a series of models, and found that several had a serious “MPG gap.” More than half the cars showed a discrepancy of at least 10% compared to the marketing (which is based on figures approved by the Environmental Protection Agency).

Ford came out worst in the reckoning. Its high-end Lincoln MKZ has a “combined MPG” of 45 (city and highway), according to manufacturer and government. Consumer Reports puts the real figure at 34–a 24.4% difference. It notes that that could mean an extra $1,510 in gas costs over five years, based on a $3.50 gallon, and 12,000 miles a year.

Likewise, Ford’s C-Max Hybrid, which is supposed to do 47 MPG, actually posts 37. And the Ford Fusion Hybrid, which advertises as a 47 MPG car, actually does 39. Consumer Reports says the hybrids are particularly under-performing in city conditions; across the models tested, they fell 28% short, on average.

Exactly what accounts for the differences is a matter of conjecture. Consumer Reports notes that its tests are slightly different to the EPA-approved versions. For one, it goes on the open-road, and takes the cars to 65 MPH, while EPA-sanctioned tests only go to 60 MPH. For hybrids, that’s quite important, as they can use battery power until 60 MPH, but need to engage the gasoline after that. So running the cars at 65 MPH obviously decreases the economy.

The more murky explanation is that the manufacturers are getting better at gaming the tests, as John Voelcker describes here. Car-makers get to choose which models they put forward, frequently use mathematical simulations instead of actual tests, and only have their work checked by the EPA 15% of the time.

The EPA says it’s sufficiently concerned about Ford’s claims that it’s looking into the matter. But meanwhile it pays to be skeptical: 37 or 34 MPG is still good, but it’s not what you hoped.

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About the author

Ben Schiller is a New York staff writer for Fast Company. Previously, he edited a European management magazine and was a reporter in San Francisco, Prague, and Brussels.

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