Outside temperature reading is higher than actual temperature

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TMK26

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#1
The outside temperature shown on my screen is higher than it actually is. For example, this morning it was 10 degrees (F) outside but the car was showing that the temp is 18 degrees (F). It actually started as showing 22 degrees but gradually went down, after driving for 20 minutes, to show 18 degrees. I notice that it's usually off by 5 or so degrees.

Is this an issues with other drivers here?
 

Wooloomooloo

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#7
Frozen ears can tell 10 from 18?
Absolutely. If it's just the tops of your ears that sting, it's about 28 degrees. If that drops around to the sides to just above the lobes, it's 22. When the lobes go numb, it's definitely below 20. When the side of your face aches, and your dangly bits (if you're a guy) have turned concave, then it's below 10.

Wind chill affects things of course, the 'feels like' applies rather than actual temp.

/j
 

kort677

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#9
the reading is not instantaneous, for example if the car was sitting in the garage it will take a few minutes to read the ambient temps outside, in addition other factors can affect the readings like direct sunlight.
 

ADK46

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#10
Since the OP referenced a reading after 20 minutes of driving, neither the transient error nor the sun can be factors (wind will erase a radiation effect, according to my sensitive ears).

Where is the sensor? If it gets loose, is there a source of heat it might contact?

Reading too high is kinda dangerous, if you use the reading to help judge the possibility of ice on the road. An error like this contributed to a ride-the-rails adventure I had many years ago during "wintry mix" conditions.
 

JWardell

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#11
Was it sunny?
Cars often have their outside thermometers under the bumper or some other panel. The cavity will heat up when sitting in the sun. Once you drive at highway speeds for a few minutes you will see it cool down. Typical of any other car I've had with exterior temp.
It's just not cool on a car to have a temperature probe sticking way out like an airplane :)
 

Mike

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#12
I have to wonder if this sensor is also involved with the BMS's reactions to the temperature around it......

It may be worth a call to Tesla.

My temperature readout seems to be within 1c of ambient.
 

John Rea

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#13
I've read that the "thermometer" on a car is electric. Meaning, it measures temperate by the way electricity flows at that time (sorry, going from memory). They don't use a legitimate mercury thermometer. So, you will get a wide range and rarely accurate.

"Pretty much all the sensors on a modern car are electronic, including temperature sensor. These temp sensors work according to a basic principle of electricity and that is temperature effects electrical resistance. Resistance will effect how much current is flowing in a circuit, as resistance goes up — current goes down; think of it like a water hose. as you create resistance in the hose the water flow in it will go down.
So how does your temp sensor work? The first resistor is located in the sensor, and the second resistor is located in the computer. The computer also has a internal volt meter built into it so it watches how much voltage the temp sensor resistor uses and its programmed to know what the temperature is based on how much voltage the first resistor, in the temp sensor, uses. "
 
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ADK46

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#14
They’re thermistors. Remarkably accurate, usually. Check out the thermometer section at your local Wally’s World.

The problem with mercury or alcohol thermometers is the attachment of the scale, and the exact diameter of the tube. Much more difficult to control than the production of thermistors. There’s even a characteristic of glass referred to in terms of its effect on thermometers - can’t remember the term right now.
 

Long Ranger

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#15
I haven't done any good tests yet, but I think mine might be reading high, too. Comparing National Weather Service readings for a few locations along my commute the last two mornings I see that yesterday NWS shows temps of 30-32F while my car showed 37-40. Today NWS was 33-36 and car showed 40-42.

Now this comparison is by no means perfect, maybe the freeway really was warmer than the NWS locations. I was just a bit surprised yesterday morning when I saw that my car was reading 38F as I drove past a spot where a bus had spun out earlier.

Drive is about 45 minutes, mix of city, traffic, and full speed freeway, but I don't really notice much temperature differential based upon conditions. Car is also parked outdoors overnight, so it's cold from the start. Currently on 2018.50.
 

alienranch

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#17
Mine is doing what the OP stated (showing from 7-10 degrees higher than true reading). I'm currently running 2019.28.3.1, but this has been happening for probably the last 2 months or so. Previously, the outside temperature listed on the console was pretty much spot on with all major weather apps. Now, it consistently shows 7-10 degrees higher all the time. Typical example - it will be 96 outside yet show 104. It's clearly not 104, the car has been in a covered garage at work where it's cool, and the reading will remain 7-10 high throughout my 1 hour drive home. If this is a known issue introduced in vX.XX, then great - I'll just wait for an update. If not, I'll probably need to call the mobile service as something has clearly changed the last couple months with that reading.
 

Madmolecule

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#19
Mine also runs 7-10 degrees hotter. I attribute it to road heat from other cars but my previous cars did not read different from the weather station/app reported current temperature. Mine also takes awhile to normalize to ambient temperature when I leave my garage. This can take up to five minutes to start reading correctly.