Felly sgrifennodd Will Hand :
If the air is quite dry and moisture around the radiator evaporates due to
increased velocity then the temperature around the radiator will fall. So the
mechanic could have been correct.

But there is no windchill effect on a dry surface. The radiator is in a fairly
dry environment, and even if it had got a bit damp standing overnight, it
would not take more than a few minutes of motoring for it to be near enough
completely dry. Any windchill effect whilst the engine is running would be
more than offset by the temperature of the engine warming up the water.

I suppose there is a possibility, in the first few seconds after starting the
engine and moving away, before the water has really started circulating, of a
brief cooling effect.

Adrian
--
Adrian Shaw ais@
Adran Cyfrifiadureg, Prifysgol Cymru, aber.
Aberystwyth, Ceredigion, Cymru ac.
http://users.aber.ac.uk/ais/weather/ uk