[jeff_tyrrill]

100% of the energy becomes heat eventually. For a typical trip, this happens by the trip conclusion. (And also each time the car pauses, such as a stoplight.)

For the trailer-on-hill example, it concludes when the trailer (eventually) is towed or rolls down the hill and comes to a rest from friction.

The weighted trailer is being used like a battery and modifies the situation in the same way as if it were a hybrid car (non-plug-in battery that recharges through regenerative braking and/or directly from the ICE).

[tzs]

If we are going to count energy that is delivered to the payload in a non-heat form that eventually becomes heat then yes, 100% of an ICE's energy from gas goes into heat--but so does 100% of an EV's energy or a bicycle's energy.

The difference between an ICE and an EV with similar sizes and shapes as far as heat goes is that although all the energy from both eventually ends up as heat the EV produces less unnecessary heat. To move the payload a given distance the ICE will use about 4 times as much energy. Only 1/4 of the energy from the gasoline goes toward accomplishing the job of the vehicle. The other 3/4 is waste heat.