A flex-fuel car looks just like any other kind of car -- which is why some people don't even realize they own one. The main differences between the two lie with the engine and fuel system. Before discussing them, let's take a quick look at what fuels a flex-fuel vehicle.
Flex-fuels can run on regular gas, various ethanol blends and other types of fuel [source: Bionomic Fuels]. Ethanol is produced by fermenting plant sugars; in the United States, ethanol's plant sugars mainly come from corn, although sugar cane and other starchy agricultural products can also be used [source: Environmental Protection Agency]. The main ethanol blends on the market today are E85 and E95, which get their names from their compositions: E85 is 15 percent unleaded gas and up to 85 percent ethanol, while E95 -- typically used in diesel-powered vehicles -- is up to 95 percent ethanol [sources: Bionomic Fuels, Clean Air Trust]
Back to the mechanics. The internal combustion engine of a flex-fuel vehicle is designed to run on more than one type of fuel -- usually gasoline plus ethanol or methanol fuel, all of which are stored in the same tank [source: Chapman]. When you start driving, a sensor mounted in the fuel line reads the fuel blend -- the ethanol/methanol/gasoline ratio, or the fuel's alcohol concentration -- and sends a signal to an electronic control module. The electronic control module then adjusts the fuel trim, or the engine's fuel delivery control, to compensate for the different fuel mixtures [sources: Heisner, FlexFuel US].
Components that comprise the fueling system of flex-fuel vehicles are also crafted to be ethanol-compatible. If they weren't, ethanol's higher water content could cause rust to form and damage the fuel system from the inside out [source: Change2E85].
Despite these different components, maintenance costs for FFVs are generally the same as for other vehicles, and sometimes are even lower, since flex-fuels burn fuel more cleanly [source: FlexFuel US].
Whether flex-fuels will become the norm in the future remains to be seen. But at least alternative fuels and vehicles are being investigated.