vehicles' real-world gasoline mileage is less than the EPA sticker number, and can often be 20% less than the sticker number depending on speed, temperature and other factors. The EPA explained that with hybrids the gap is much wider, as high as a 30% drop. Ford responded in a statement, saying that, "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." A Ford spokesman also said they followed EPA's test guidelines and the company is standing by the ratings as determined by the current testing protocols. Nevertheless, they are working closely with the agency to determine if any changes are needed for the industry relative to hybrid vehicle testing. In July 2013, Ford issued a voluntary software update for the 2013 model year Fusion, C-Max and MKZ Hybrid, that attempts to improve on the lower-than-expected MPG claims. Some of the changes include: Increasing the maximum pure electric speed from , allowing increased use of electric-only mode on the highway Optimizing the use of Active Grille Shutters to reduce aerodynamic drag under more driving and temperature conditions including cold weather, during air conditioner use and when the engine coolant temperature is higher Reducing the electric fan speed as a function of coolant temperature to minimize the fan's energy consumption Shortening engine warm-up time by up to 50 percent to enable electric-only driving and engine shutdown at stops sooner after cold starts Optimizing the climate control system to minimize use of the air conditioning compressor and reduce the energy used in cold weather operation. In August 2013, and due to the criticism and after several lawsuits about the worse-than-expected fuel economy, Ford voluntarily lowered all three EPA ratings of the C-Max Hybrid and will pay about a rebate to some 32,000 C-Max owners. The revised fuel economy ratings for combined was lowered from to . Ford has no plans to change the fuel economy ratings on the 2013 Fusion hybrid, because the company used the Fusion hybrid test to generate the fuel economy label for the C-Max Hybrid following EPA's rules. Ford Fusion Energi The Fusion Energi is a plug-in hybrid unveiled at the 2012 North American International Auto Show, and retail sales in the U.S. began in February 2013.