tihsyloh

Has anyone else noticed that our cars might say it is 95 degrees outside but every bank sign and radio station says it is only 89 degrees? How exactly does the gauge work? Does it factor in heat index or chill factors or just ambient temperature? How does it get an accurate reading when I am driving 75mph and the engine bay, which is where I assume the sensor is, is being flooded with wind which I would think would lower the temperature on the sensor? If the sensor is secluded somewhere where wind is not a factor, doesn't the engine heat the "trapped" air thus causing a higher temp reading?

I find this feature to be somewhat useless because I beleive there to be about a +/- 10 degree margin of error.

Am I making any sense?

mjbrox

you make sense......I think it is wrong also

denVerSlube

It's been posted here that the sensor is right behind our big fat North American license plates.

I asked at the dealer if they could change the bias offset constant with the VAG, and they said "No - we can't do that." Being an embedded software guy (satellites/rockets) I find that hard to believe - but maybe it's not b.s.

Silver Streakin'

I thought it messured the air closest to the ground for road temps. not air temps.

tihsyloh

Neat sig. It has a strong resembelance to a MA title.

shaggymatt

Which is what about a foot off the ground. Bank signs are elevated, and sitting in direct sunlight all day. Furthermore, your radio station might say it is 90' and you read 95'. Where is the temperature being read? In our situation, the reporting station is outside the city, at an airport, you had better bet with the urban heat island the city's temp will be higher.

Thermometers do not care about "wind chill" so no matter how fast you are going it will read the same temperature. If you have a wet bulb thermometer, it would be affected by the wind.

To top it all off, thermometers are not calibrated at the factory, so deviances would be expected. In my first meterology course I took in college, we did tests on that actually. The variances were up to 5'F between the same brand thermometers bought all at the same time. And yes my professor was a biggie against the global warming theory partially for that reason!

HDClown

The past few days mine guage has read 99/100 and it's only about 90-92 outside in reality. Since it's in front of the radiator, it's picking up heat off that, and engine heat.

The probe gives it most accurate reading when your moving at a good speed for a minute or so because the window coming into it helps adjust it to a proper temp.

I view mine as a "feels like" temperature Because most of the time it's register what it actually feels like outside ,not what it really is.

tihsyloh

In my case, I live in Downtown KC, MO and they report readings in three parts of the city as well as outlying areas, so I feel reasonably comfortable that that is not a factor with me.

Although I believe you, I am still a little baffled by the fact that moving air would not reduce the reading. It's like planes, I know why they fly, but it still amazes me every time I watch one take off.

Try this example. If it is 30 degrees farenhieght with no wind, an electronic temperature gauge would indicate 30 degrees. Now if there was a 20 mph wind passing over the sensor, wouldn't that indicate a lower temp such as 28 degrees. If I were to rub the sensor on a piece of carpet, it would indicate a higher temp as the friction would produce heat on the sensors tip. Same line of thinking, if a cold wind is passing over a sensor, it seems to me that that would indicate a cooler temp. Therefor, might the car try to factor the temp the sensor is reading, the speed at which the car is traveling, and the heat produced by the engine and attempt to make an educated guess as to what the temp is. This would certainly justify any inaccuracy.

Or am I just making this a lot more complicated than it really is? Hey, we don't learn anything if we don't ask questions.

AudiduA

all the talk about temp at road surface and bank signs and why there are variances is garbage. Both my Mom's Lexus and my Dad's Acura don't have this problem at all. The outside temp indicators in those cars usually match the bank signs and the radio (or are within a degree or two).

The outside temp indicator in the A4 consistently reads 5-10 degrees higher than all other indicators (including what I would guess the temp to be without having a thermometer available).

I definitely think the US front plate blocks airflow to the sensor. I actually moved my sensor to a position where it gets much better airflow. It came out of it's little bracket quite easily and I strapped it to one of the slats in the lower grill. I think it has helped somewhat. The temp still reads higher, but not as much as before, and it tends to come down more when the car is moving.

I agree with another poster that there is an electrical impedence or bias error in the sensor. Asking a service manager about making an electrical circuitry adjustment though is utterly useless.

It is just another little quirk in our Audi's that we really should not have to put up with (IMHO).

Deerslayer

Wind feels cool beause the moisture on your skin is evaporating faster. Assuming your sensor is dry, wind speed has no effect.
I don't trust the reading from mine either. A couple of weeks ago, it was overcast; I'd guess the temp was in the high 80's. When I pulled out of a parking lot, the temp read 101... then it slowly climbed to 104.