Flex-fuel technology refers to a type of vehicle that has an internal combustion engine that can run on either gasoline or up to E85 gasoline-ethanol blend. A sensor in the fuel system measures the ethanol content in the fuel, allowing the engine's control unit to adjust the engine's tune accordingly.
Flex-fuel vehicles can run on E85 without any difference in performance. Although flex-fuel vehicles can run on pure ethanol, blending ethanol with gasoline ensures that the vehicle can start in cold weather. Since E85 has less energy per volume than gasoline, there is a 30 percent decrease in miles per gallon while running on E85 versus using gasoline. Despite this drawback, ethanol is used because it is a renewable energy source that produces fewer greenhouse-gas emissions than gasoline.