If an automobile had a 100% efficiency, 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 make any noise? would it vibrate? would any of its fuel go unused?

 

Answer

In the engine,fuel energy is converted to kinetic energy of the vehicle,it is used to overcome the friction of the road.this is the main purpose of the engine.Besides this the energy of the fuel is wasted as sound produced,heat produced in the engine etc. if an engine was 100% percent efficient it would not waste any energy and all the energy would only be used to overcome friction and to impart velocity to the vehicle.so,no heat or sound would be produced.also,there would be no vibrations.and no fuel wold be wasted.