There can never be a perfect machine though. There will always be waste in a system and cars always have waste. Most of the waste a car puts out is in the form of heat. Heat is a common form of energy loss from a system. There is no way to conserve the heat loss from a vehicle either. If people could store the heat loos from a car and find a way to convert that back into useful energy, that would give us some serious gas mileage.