"Adrian D. Shaw" wrote in message
...
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.

Yes fair enough the radiator will warm quickly and dry. I was only suggesting
how the mechanic could have been right.

Cheers,

Will.
--

My Astra has a factory fitted one with a resolution of 0.5 deg
C, that too is
very accurate (measured against screen and AWS). I have no
idea where that is
mounted but it works in all weathers, a little snow symbol
even lights up when
it falls to 2 deg C which is fun in winter!
Will.

Mine beeps at me when the temperature falls to 3.5ºC. In my
previous car the display started flashing, and produced a little
snowflake symbol, when it fell below 4ºC.

At what temperature ought one to start thinking about ice on the
road? I would have thought 4ºC because that's the point at which
water starts to expand again??

Anne

"Anne Burgess" wrote in message
...
My Astra has a factory fitted one with a resolution of 0.5 deg
C, that too is
very accurate (measured against screen and AWS). I have no
idea where that is
mounted but it works in all weathers, a little snow symbol
even lights up when
it falls to 2 deg C which is fun in winter!
Will.

Mine beeps at me when the temperature falls to 3.5ºC. In my
previous car the display started flashing, and produced a little
snowflake symbol, when it fell below 4ºC.

At what temperature ought one to start thinking about ice on the
road? I would have thought 4ºC because that's the point at which
water starts to expand again??


Anne yes 4 deg C would be about right for untreated road surfaces.

Will.
--

On Sat, 10 Jun 2006 09:14:58 +0100, "Will Hand"
wrote:

Yes fair enough the radiator will warm quickly and dry. I was only suggesting
how the mechanic could have been right.

....but the radiator doesn't warm up quickly. The radiator only warms
up after the cylinder head thermostat opens and diverts hot water in
the cylinder block through the radiator. Under freezing conditions,
this can be some minutes after the engine fires up.

Try this. The next time you drive in cold weather keep a close eye on
the temperature gauge. The temperature will rise to almost normal,
then drop back and then continue its rise. The point at which it drops
back is when the head thermostat opens allowing cold water from the
radiator to circulate around the block and, in so doing, temporarily
reduces the water temperature in the block. The water temperature then
continues its rise until a state of equilibrium is reached, that state
being determined by the setting of the head thermostat.

Having said all that, the thermal mass of the water filled radiator
mitigates against any significant cooling effect generated by the
evaporation of an external film of water.

--
Alan White
Twenty-eight miles NW of Glasgow, overlooking Lochs Long and Goil in Argyll, Scotland.
Web cam and weather:- http://www.windycroft.gt-britain.co....her/kabcam.htm

Anne yes 4 deg C would be about right for untreated road
surfaces.
Will.

Thanks Will. Not that there's any need to worry today - it was
registering 23.5ºC right on the coast just now.

Anne

Anne Burgess wrote:
Anne yes 4 deg C would be about right for untreated road
surfaces.
Will.

Thanks Will. Not that there's any need to worry today - it was
registering 23.5ºC right on the coast just now.

Anne

The relationship between air and road temperature is not fixed, it is very
dependent on road construction, state of sky, evaporative cooling, season,
sky view etc. Overcast skies and an air temp of -1C can be associated with
positive roads, and a air temp of +4C in a breezy, low dewpoint airmass with
evaporative/radiational cooling can lead to road ice.

--
Stuart Brooks
Carluke
South Lanarkshire 223m amsl

webcams at
www.brooks22.plus.com/index.htm
INC new high res webcam

wrote:
Dennis wrote:
How accurate are standard equipment car thermometers ? Mine today,
in a Rover 75 at 4PM in SW Wales, was showing 29 degrees, is this
likely to be accurate, or are car thermometers known to over or
under record ? Thanks

My Mondeo thermometer has an accuracy to around 1 degree, as it
usually agreed with the screen temperature at Cardiff when I went to
work. Mind you, the screen was on the 12th floor roof. However, over
a period of years the car thermometer seemed to perform very
accurately.

It was interesting monitoring the temperature changes on the journey
between Bristol and Cardiff, espcially early mornings. I was rather
surprised that the temperature on one certain stretch of motorway
being persistently lower than the rest of the journey, and
occasionally up to 7 degrees lower in the winter. I wonder if you can
estimate where this was?

Underwood or Greenditch?

I've gone through about 10 car thermometers in the last 20 years! Annoyingly
the last one I got only had a resolution of 0.5C. While absolute accuracy is
only around 1C this varies according to the sample, some are spot on, some
have a bias, this possibly varying according to temperature. This means
calibration is possible, so it is very annoying to find that the latest
Maplin model has been degraded. It should also be easy to add in to the
thermometers memory user programmable calibration factors but noone has some
out with such a product yet.

So far I've just been hanging the wire out the car window, this is why they
don't last long as eventually the cable gets damaged. Those of you who have
run the wire to the front bumper, how have you routed/secured the wire so
that it stays clear of moving or melty bits of the engine?

--
Stuart Brooks
Carluke
South Lanarkshire 223m amsl

webcams at
www.brooks22.plus.com/index.htm
INC new high res webcam

On Sun, 11 Jun 2006 00:34:26 +0100, "Stuart Brooks"
wrote:

Those of you who have
run the wire to the front bumper, how have you routed/secured the wire so
that it stays clear of moving or melty bits of the engine?

Silly answer, but made sure it was clear of moving or melty bits of
the engine. The ones that I've used from Maplin, which seem to be no
longer available, always had ample lead length so that it was fairly
easy to route the cable close to the bodywork looping it around useful
brackets and things to secure it. As I said in an earlier post, the
problem in modern cars is gaining access to the engine compartment
from the passenger compartment. Some years ago it was possible to find
where the main cable harness went through the front bulkhead and to
force the sensor through the same route. Nowadays there seems to be
more trim and use of multiway connectors which prevent that approach.
I bought my #2 son a thermometer for Christmas and, so far, he hasn't
been able to install it.

--
Alan White
Twenty-eight miles NW of Glasgow, overlooking Lochs Long and Goil in Argyll, Scotland.
Web cam and weather:- http://www.windycroft.gt-britain.co....her/kabcam.htm

Stuart, my apologies for that first sentence. I must not post before
breakfast...

--
Alan White
Twenty-eight miles NW of Glasgow, overlooking Lochs Long and Goil in Argyll, Scotland.
Web cam and weather:- http://www.windycroft.gt-britain.co....her/kabcam.htm

wrote:
I was rather
surprised that the temperature on one certain stretch of motorway being
persistently lower than the rest of the journey, and occasionally up to
7 degrees lower in the winter. I wonder if you can estimate where this
was?

The M49 by Avonmouth, especially in a slack NW'ly. I know the Estuary
is only about a mile wide at this point, but I would have thought a
slow drift from the W or NW would have had some influence, but
seemingly not. I had a few mornings when the temperature at Avonmouth
was minus 1 C, but Cardiff city centre was plus 6 C.

Strangely, a NE'ly (which you might think would produce lower
temperatures in the west) made very little difference.