snip/ Suddenly, as I turned around and drove with the wind behind me, it
moved up to about 3/4 way up the dial.  But as soon as I turned back to
windward, the temp. came down again. The fan is working (though maybe a bit
noisier than before?) but doesn't seem to be switching on for as long as
before. I'm getting it looked at tomorrow, but suspect the little temp
sensor switch screwed into the radiator, that turns the fan on.  Does this
sound reasonable? Any ideas most welcome! Bob /snip

it sounds reasonable but then it might be a clogging radiator, ever use that
stop leak stuff before?  When you remove that sender, check for excessive
amount of goop on the area that faces inside the radiator, might just be a
hint of what else is in there.  Clean sensor? OK, how about removing the
grills and eyeballing the condenser and radiator fins for bugger
build-up...tip-dropping the condenser aids in cleaning the fins on both
items and prolly hasn't been done in years and can be done without opening
a/c system.
I think the wind matters little unless there was a significant ambient
temperature drop as well.  The radiator needs airflow to displace heat and
at cruising speed with the wind at your back, there would be enough airflow
to displace heat on the radiator surface.  If cruising speed and wind at
your back are matched, the radiator fan would still operate (if the radiator
is not clogged and temp sensor operational and it gets warm enough) to
displace heat on the radiator surface.
OK, back to tractors.

JB
'89 Wolfsburgs, one with new radiator and most everything else-normal
operating temperature, one with no new parts in awhile and PO introduced
stop leak-varying operating temperature and goopy insides.