in the time that the Ford C-Max has been on the market, a significant portion of owners have complained that they weren't able to get anything close to the last year's EPA ratings of 47 mpg city, 47 highway.
For the 2014 C-Max Hybrid, Ford was forced in August 2013 to lower its ratings to 43 mpg combined (45 mpg city, 40 mpg highway). The reduction came after Ford admitted that it had used the gas-mileage figures for the 2013 Fusion Hybrid sedan, which fell into the same weight class and used an identical powertrain. That practice was entirely legal under EPA rules, but after widespread buyer complaints and an investigation by the EPA into its real-world fuel economy, the company agreed to lower the ratings.
Simultaneously, Ford has introduced gearing changes that should keep the four-cylinder engine at lower revs; a host of minor changes that should help aerodynamics; and a new engine oil for reduced friction—all changes that should help close that discrepancy between the official estimates and real-world results.
UPDATE: In June 2014, Ford again lowered its ratings for the 2014 C-Max Hybrid--this time to 40 mpg combined (42 mpg city, 37 mpg highway) after discovering errors in lab-test measurements and calculations for aerodynamic drag. Ford agreed with the EPA to reduce the ratings a second time, and send a check for the increased gasoline costs to all owners of 2013 C-Max Hybrids, along with five other cars whose ratings were reduced at the same time. While 40 mpg is still higher than the majority of cars on the market, it is a lower rating than the larger (if less powerful) Toyota Prius V wagon.
UPDATE: As for the C-Max Energi, efficiency ratings for the plug-in hybrid mdoel were lowered to 38 mpg combined (88 MPGe efficiency, 19 miles electric range) from 43 mpg combined (100 MPGe efficiency, 21 miles electric range). MPGe, or miles per gallon equivalent, is a measure of how far a car can travel electrically on the same amount of energy as is contained in 1 gallon of gasoline.
In our road tests of the Energi model, we've seen gasoline-only mileage averages in the same range as the Hybrid model—in the upper 30s to around 40 mpg on gasoline alone. In both models, you get a special Eco Coach set of displays, oriented toward helping you understand the power flow of the powertrain and optimizing your use of charging, and of the hybrid system.