Question

If an automobile had a 100% efficient engine transferring all of the fuel's energy to work, would the engine be warm to your touch? Would its exhaust heat the surrounding air? Would it vibrate? Would any of its fuel go unused?
There are really no 100% percent efficient machines, are there??

Answer 1

The exaust temp would be zero K. The engine would be at the same temperature it started at (probably O K, the exaust temperature)
It could not vibrate, that takes energy.