The message
from "Dave Plowman (News)" contains these words:

That's a bit of an over simplification. Engines don't run at their most
efficient until up to temperature. Probably to do with proper atomisation
of the fuel.

Partly that, but mostly because it's the difference between the incoming
cold charge and the hot burning that generates the power. Designers now
keep the engine as hot as practial in order to keep the gases as hot as
possible during the power stroke so that they're only cooled by
expansion instead of radiation/conduction/convection. It's the
efficiency of expanding the hot gases which drives the efficiency of the
engine as a whole.

Obviously there are many other considerations, but that's the
fundamental thermodynamic one.

--
Skipweasel
Never knowingly understood. (Ivor Cutler)