[nynor]

gasoline to mechanical energy = 30% efficiency (someone will probably correct me), in an internal combustion engine. this isn't going to change. the rest is lost as heat, hence the relatively large radiator and coolant reservoir.

bmw was (is?) trying to do something with this heat by using it to create HP via steam. it looked VERY complicated to me.

edit: i was optimistic, it seems: 15%

http://www.fueleconomy.gov/feg/atv.shtml