Johannes wrote:
Chris Bacon wrote:

Ian Stirling wrote:
Current car engines are about 25% at best efficient, so 75% of
power goes out the exhaust pipe wasted.

I thought most was lost through the radiator.

Strangely enough, cooling though the radiator is just as important as
the heating in the combustion for achieving high efficiency. You can
only extract mechanical energy between two temperatures; the larger
the gap, the more efficient.

So what does the radiator cool that forms the 'cold' part of that pairing?