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Author Topic: Why Does The Car Temperature Thingy Change After Driving a While ?  (Read 5413 times)

Offline neilep

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Dearest Car Thermometer Temperatureologists,

As a sheepy, I of course luff thermometers. Thermometers are my all time favourite way to tell how how or cold something is in a temperature displayed kind of way !

Look..I just got in from being out in our carmobile !

Here is the temperature at a blistering hot 0'C


It's Cold !

Sorry for the crapo piccy but ewe try driving at 60mph in a 30mph zone when the windows are all misted up on ice infested roads in the dark with one hand whilst attempting to photograph the temperature thingy !





....now then, only a few minutes before when I started the car it said it was 2'C !....It's not that there was a dramatic temperature difference whilst I was driving...this always happens !!...be it summer or winter !

Why does the temperature change after a few minutes ?...where is the car thermometer thingy and what does it look like ?


Thanks for this....drive carefully now won't ewe ?




Hugs & shmishes


mwah mwah mwah !!




neil
Who's Gonna Take ewe Home  ?
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Offline LeeE

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If it was not too windy then the air beneath the bonnet would have effectively been trapped there while the car was stationary.  If the bonnet absorbed any solar energy, this may have been enough to raise the temperature of the trapped air.  When ewe started driving though, this warmed air would have been flushed out; cooling air is designed to flow through the engine bay.  It's likely that the ambient temperature sensor is somewhere inside the bonnet, as there's already a wiring loom running there and it would need to be shielded from the wind, albeit in a 'cool' zone where heat from the engine won't effect it.

Conversely, if the temperature sensor is just attached to the inside of one of body panels (which would require an additional wiring loom), then it might just be wind-chill that causes the temperature reading to drop.
 

Offline neilep

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Fantastic Info ..Thank ewe very much LeeE

So, underneath the bonnet eh ?...lies a secret thermometer type thingy.

yes, Yes, I see completely now, your explanation is great. Though it was at night so this would preclude solar energy yes ?...would latent heat from the engine add a degree or two ?...hmmm *sheepy ponders*...how does that account for when the car has been left overnight ? Perhaps that is when the solar heat comes into effect when it becomes day !

 

Offline graham.d

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My temp sensor does the same thing. I am fairly sure it is direct heating by the sun and that it is only accurate when the car has been moving for a minute or two. A simple experiment would be to see whether the value changes (stationary to moving) at night.

I don't see how wind chill would have any effect on a thermometer, Lee. There is no temperature change with wind chill, it is just that the wind removes heat from a warmer body faster than still air. I guess there could be cooling from evaporation of moisture but then the temperature would go up again once the moisture had gone, but that is not what I observe.
 

Offline neilep

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Thank Ewe Graham.....I am comforted that yours' displays the same phenomena...at least I know mines not broken.

This was in fact at night...there could not have been any solar energy to heat the sensor.
 

Offline graham.d

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Ah. That bu**ers my theory then :-) I can only think of two possibilities. One is that the electronics operating the thermometer takes a while to settle after having been powered up and the other is that where the car was parked was locally a little warmer than road you drove along. The latter is possible because the sensor will be shielded to some extent from the outside air which may well be cooled more than the solid objects immediately surrounding the it. Perhaps you could see if the same thing happens in the early morning.
 

Offline LeeE

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Yeah - I wasn't sure about the wind-chill effect, other than just because the car isn't at 0K it has heat to lose.
 

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