On 8 Jun 2006 13:41:24 -0700, wrote:


Les Hemmings wrote:
My car
doesn't have a thermometer and I was thinking of adding one of those digital
ones with a probe on the end of a wire. Anyone tried this with any success?

I have bought them from Maplin (cost around a tenner).

First thing is to calibrate (well sort of calibration) by finding the
error when the probe is in melting ice - it should of course be zero
C (distilled or previously boiled water). You then have a rough guide
as to the error.

The temperature readings cannot be expected to have absolute accuracy,
but do permit comparisons. I have determined the local hot (and cold)
spots for example.

I have mounted the probe beneath the door mirror in the airflow.
Airflow is essential - readings are meaningless when the car is
parked. Occasionally, when the sun is shining on the probe, it will
over read even when moving.

Don't be confused about cooling or heating as a result of the
airflow. At normal motoring speeds, the effect can be ignored. At
aircraft speeds (pilots apply corrections) it does become a factor from
about 150 mph upwards.

Is that due to compression ahead of the probe or friction, I wonder
Jack?

A very senior Met Office scientist I knew used to ask potential
candidates for stream 1 (as it then was) posts a fairly simple
question:

What happens to the recorded temperature of a thermometer in a wind
tunnel when the wind speed is increased?

Reflecting the current poor performance in science many candidates,
some of them with top physics degrees, used to answer, somewhat
intutitively but totally incorrectly, that the temperature would fall.

Martin




Jack

"JPG" wrote in message
...
Reflecting the current poor performance in science many candidates,
some of them with top physics degrees, used to answer, somewhat
intutitively but totally incorrectly, that the temperature would fall.
I had an argument with a mechanic a long time ago; he swore blind that car
radiators could ice up even if the air temperature was above freezing due to
wind-chill effects.

Darren Prescott wrote:
"JPG" wrote in message
...
Reflecting the current poor performance in science many candidates,
some of them with top physics degrees, used to answer, somewhat
intutitively but totally incorrectly, that the temperature would
fall.
I had an argument with a mechanic a long time ago; he swore blind
that car radiators could ice up even if the air temperature was above
freezing due to wind-chill effects.

My old Volvo's carb used to ice up due to the evaporation of petrol even on
summer days. I suppose if the radiator had a leak and the ethylene glycol /
water mixture evaporates fast enough you could get below ambient. But then
the engine is pumping heat into it hand over fist anyway, so probably not.
The strangest feeling with the wind chill effect was a VERY hot summer's day
blatting down from the Plume and Feathers at Princetown to Paignton sea
front on the back of a Kawasaki Z750. We really didn't hang about and it
gets pretty cold as the sweat evaporates. I still remember getting off the
bike shivering, surrounded by people in trunks, soft tarmac and sun tan
lotion. Feeling the heat creep back in. Very odd....

Les


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Les Hemmings a.a #2251 SA

"Darren Prescott" none@no,dns wrote in message
...
"JPG" wrote in message
...
Reflecting the current poor performance in science many candidates,
some of them with top physics degrees, used to answer, somewhat
intutitively but totally incorrectly, that the temperature would fall.
I had an argument with a mechanic a long time ago; he swore blind that car
radiators could ice up even if the air temperature was above freezing due to
wind-chill effects.



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.

Will.
--


" You cannot count your life a success unless you can find one person who says
that they are happier because you were born "
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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
--
Teachers & critics, all dance the poot. Are we not men ? We are Devo.

Perhaps you should mount a Stephenson's Screen on your roofrack and put
the thermometer in there

Generally the rule is that they are not accurate when the car is
stationary but tend to be +/- 1/2C when you are on the move.

For the weather enthusiast they tend to be like hotel bar thermometers
on holiday and provide the normal punter with another way to irritate
greatly when talking about weather ("it was 140 C in Turkey when I was
there in March"...."my car said it was 32 C today when I was at Tesco's
in Blairgowrie" and so forth)



brian
aberfeldy


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

Purbeckview 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
--
Teachers & critics, all dance the poot. Are we not men ? We are Devo.

Perhaps you should mount a Stephenson's Screen on your roofrack and put
the thermometer in there

That has been done, believe it or not, in the days before electronic
car thermometers when exploring local temperature differences was a lot
harder and neede much more tenacity. The name escapes me. A very
pleasant and enthusiastic man who trialled his own electronic
thermometer alongside standard kit on his car roof.
He tried it mainly in Dublin if I remember correctly and mentioned it
many years ago at one of our Metsoc meetings in Durham, or was it at an
annual COL meeting?. He has posted on this ng, again many years ago,
and had a very accurate humidity / dew point etc calculator on the web.
He did try to explain the mathematics behind it all. That was lost on
me, but his enthusiasm wasn't.

Best wishes,
Ken
Copley, 253metres asl, nr Barnard Castle, County Durham
http://copley.mysite.orange.co.uk

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

Les Hemmings wrote:

sources, free from warm air, clear of the road and in the shade. My car
doesn't have a thermometer and I was thinking of adding one of those digital
ones with a probe on the end of a wire. Anyone tried this with any success?

I too have fitted one of the Maplin ones, with the sensor behind the
front bumper. It seems to be reasonably accurate on the move or in the
shade when the engine is cold, but warms up quite rapidly when standing
in traffic.
--
Steve Loft, Glenlivet. 200m ASL
Weather and webcam:
http://www.livet.org.uk/weather

"Steve Loft" wrote in message
news
Les Hemmings wrote:

sources, free from warm air, clear of the road and in the shade. My car
doesn't have a thermometer and I was thinking of adding one of those digital
ones with a probe on the end of a wire. Anyone tried this with any success?

I too have fitted one of the Maplin ones, with the sensor behind the
front bumper. It seems to be reasonably accurate on the move or in the
shade when the engine is cold, but warms up quite rapidly when standing
in traffic.
--

I have a Radio Shack thermo which gives changes at 0.1 deg C intervals,
extremely accurate tied to the wing mirror of my Fiesta, but suffers in direct
sunlight of course.

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.
--


" You cannot count your life a success unless you can find one person who says
that they are happier because you were born "
-------------------------------------------------------------------------------
A COL BH site in East Dartmoor at Haytor, Devon 310m asl (1017 feet).

mailto:
www: http://www.lyneside.demon.co.uk/Hayt...antage_Pro.htm

DISCLAIMER - All views and opinions expressed by myself are personal
and do not necessarily represent those of my employer.
-------------------------------------------------------------------------------