An alternative fuel vehicle with a flex fuel system, also known as a dual fuel system, has an engine system that is engineered to run on more than one fuel, primarily gasoline blended with either ethanol or methanol up to 85%, and both fuels are kept in the same common tank. Also, flex-fuel vehicles differ from bi-fuel vehicles where two fuels are stored in separate tanks and the engine works on one fuel at a time, such as compressed natural gas (CNG), liquefied petroleum gas (LPG), and soon.