By John Ostapkovich

By John Ostapkovich

PHILADELPHIA (CBS)  —  A Federal civil suit is awaiting action in Philadelphia, with some consumers saying two Ford hybrid vehicles don’t deliver on their mileage claims.

A look into the fuel economy shows some surprising things.

The Environmental Protection Agency doesn’t do most of the tests.

The manufacturers do, based on EPA methodology, with the agency checking 10 to 15 percent at its labs.

Temple mechanical engineering professor Richard Cohen says standardization is the right way to go.

“I can’t think of any other way to do it because, once you define the system, the auto companies can game it, and of course they can game this system somewhat as well,” Cohen said.

Ford says its testing complies with EPA rules.

The mileage measurements involve putting a vehicle on a device called a dynamo-meter  accelerating, slowing, coasting and cruising for pre-set times.

The result is a fuel economy number, but the real world is a different animal, where terrain, temperature, weather, driving habits and fuel quality impact mileage.

“And that can vary by 50% depending on how people drive.”

The EPA updated its test methods in 2008 to be more accurate.

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