We all know that combustion engines aren't efficient. In fact, despite the myriad technologies that we've developed over the decades to improve them, they still only operate in the 20% to 30%
efficieny range. That means that for every gallon of fuel you use in your car, 70% to 80%
of the energy is lost to heat and friction and the little fairies that live in your vents. Wikipedia tells us
Most steel engines have a thermodynamic limit of at most 37%. Even when aided with turbochargers and stock efficiency aids most engines retain an average efficiency of about 20%
Four fifths of the fuel you buy is meaningless. You may be paying $4 a gallon for fuel, but you're really paying $20 a gallon of "usable" fuel.
As if that wasn't bad enough, you can see it in other large industries, like energy. If we listened in high school than we know that powerlines aren't 100% efficient and if lose of heat energy happens in combustion engines than surely burning coal, oil, or gas will have some lose as well. That's true to a large extent, nicely summarized in this NYTimes graphic
:67% of the energy in our fuels is lost, out the door, out the window, into the bright, hot, wet American summer.