A U.S. automobile executive said Ford Motor Company was reviewing vehicle mileage tests in the wake of a challenge to ratings listed for two hybrid cars.
Automobile companies test their own fuel efficiency following federal procedures. But last week, Consumer Reports said it found the mileage ratings listed for the Ford C-Max hybrid wagon and the Fusion hybrid to be well off the mark.
The C-Max, tested by the consumer magazine, achieved 37 miles per gallon, ten miles per gallon less than what was on the sticker.
Consumer Reports said the Fusion achieved 39 mpg. It is also listed as able to achieve 47 mpg in fuel efficiency.
Although an Environmental Protection Agency spokesperson declined to comment on whether it was discussing the tests with automakers, Ford's global product chief Raj Nair said, "We are working closely with industry to see if we need to change our hybrid testing procedures," The Wall Street Journal reported.
Nair said mileage testing for hybrids was far trickier than testing a conventional gasoline-powered engine due to the many variables that come into play.
The expression, "your mileage may differ," is particularly true for hybrids, Nair said.
The variables include how fast a driver accelerates and what speed is maintained. The temperature outside also changes mileage for cars using battery power, he said.
Fuel efficiency can also change depending on how many of the miles are driven on a highway and how many are driven under city conditions, the same as gas-powered cars. However, for hybrids it also depends how many of the highway miles were driven with the batteries running.
If the batteries run first with the gasoline engine kicking in as electric power wanes, then a hybrid would get higher efficiency going from highway driving in the first part of a trip to city driving in the second part than it would if it traveled in the city first and on a highway second.
Testing by Ford, following EPA recommendations, was done on stationary machine that simulates highway and city conditions. Consumer Reports, on the other hand, hits the road, testing cars on rolling hills, holding to a steady 65 mph when it tests cars on highways.