5. The cost to turn a car into a Flex-Fuel or E-85 (85% Ethanol and 15% Gasoline) car is only about $200 for a manufacturer. E-85 is a bit more corrosive to some of the standard rubber and metal parts, but still the cheapest way to go “green”. The problem is ethanol contains slightly less energy than gasoline(whereas diesel has slightly more than gas) and so you need about 20%-30% more fuel running through your injectors for the vehicle to run on E-85 . If you try and run E-85 in a vehicle not designed to run E-85 you’ll see your Check Engine light come on in all its glory. Your car’s computer is telling you that the vehicle is running lean (meaning not enough fuel). I thought being “green” was all about being efficient? Ethanol is obviously not the most efficient way to go. Although I think biodiesel is up to the task.