CR reports that the 10-mpg difference recorded with the C-Max represents "the largest discrepancy between our overall-mpg results and the estimates published by the EPA that we've seen among any current models." For reference, the Toyota Prius came up six mpg short of EPA estimates under CR's testing.
So, what happens if the EPA finds a discrepancy in Ford's mileage claims? According to The Detroit News, automakers may face civil penalties over misstated claims. Just a few weeks back, Hyundai and Kia were found to have overstated mileage estimates for 1.1 million vehicles sold in the US and Canada, prompting the automaker to compensate owners for their now-reduced mileage figures. Lawsuits, reductions in consumer confidence and even inquiries from politicians are also potential problems in the pipeline.
It's too early to suggest such drastic measures will be taken by Ford, especially since "a hybrid vehicle is going to be far more variable than a conventional vehicle" when it comes to observed fuel mileage, according to Linc Wehrly, director of light-duty vehicle center compliance division at the EPA's Ann Arbor laboratory.
Ford, for its part, issued the following statement to Consumer Reports: "Early C-Max Hybrid and Fusion Hybrid customers praise the vehicles and report a range of fuel economy figures, including some reports above 47 mpg. This reinforces the fact that driving styles, driving conditions and other factors can cause mileage to vary."