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Outside temperature accuracy

Discussion in 'Model 3' started by funchess, Jun 8, 2018.

  1. SigNC

    SigNC Active Member

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    I don't mind the temp being off when i get in the car after it's been parked. All cars have that issue. What bothers me is the fact it reads 10 or 15 degrees higher than it should after driving a decent amount of time.
     
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  2. novox77

    novox77 1.21 Gigawatts

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    radiative heat transfer requires line of sight. it would have been trivial to just shield the thermistor. Hard to imagine this is the actual problem.

    I don't have a problem with the temp reading being inaccurate when I first get into the car on a hot day. I would expect that some convective force from driving would bring the temp down to the ambient air temp that's causing the convection. That shouldn't be hard to do.

    I'm also seeing very precise but +5F inaccurate readings. If this is true across all model 3s, they should just put in a -5F fudge factor in the firmware. problem solved :D
     
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  3. Saghost

    Saghost Well-Known Member

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    What reference are you using to decide it is inaccurate?

    As discussed above, the temperature of the air over the road on a sunny day is often well above the temperature posted by weather services for shaded areas.
     
  4. novox77

    novox77 1.21 Gigawatts

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    thermometer out the window, actually.

    and what prompted me to do something that silly was due to my awareness of temps I can tolerate without feeling hot. I've done lots of rides without A/C to test efficiency. And so when I see the car read 92F and the windows are down, and I'm not breaking out in a sweat, I get skeptical.

    Temps of the air over the road is definitely hotter, particularly when the sun is out. But on a rainy day, there should be no measurable difference. And the car temp is still higher than it should be. Almost feels like a calibration issue.
     
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  5. t3slatx

    t3slatx Member

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    It's always been an issue with mine, most of the times it shows +10 degrees higher. I think the temp sensor is inside the frunk, I put a thermometer in there and it seems to be around the same. Maybe it's a design flaw.
     
  6. apacheguy

    apacheguy S Sig #255

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    Yep. I never bother looking at the temp until I’ve been driving for at least 10 min. Even then, the M3 reads several degrees warmer than actual ambient.
     
  7. apacheguy

    apacheguy S Sig #255

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    That would be dumb. Why would they have put it inside the frunk?
     
  8. Big Dog

    Big Dog Active Member

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    Perhaps true, but other cars that I have owned had with a temperature gauge that shows +/- one degree from ambient temp (after driving for few minutes), so it can be done.
     
  9. Rusty1

    Rusty1 Member

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    Many times our Model 3 is +10 degrees. My Model S is much more accurate. If the 3 can’t do better than this, I would prefer a close by weather station reading.
     
  10. rsomrek

    rsomrek Member

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    Temperature is rarely measured using liquid-in-glass (mercury or alcohol) thermometers anymore. "Official" National Weather Service measurements are made using thermistors housed in a (generally aspirated) shelter well above the ground and placed over grass. The thermistors perform well and show no bias from daytime to nighttime when installed as prescribed.

    An average temperature around the car would require several thermistors and I suspect there is no real need for such overkill. Generally, ICE car readings are based on the car's need to know ambient temperatures for proper combustion given current conditions. While I don't actually know the location of the M3 sensor, I suspect it is near/behind the cooling vents at the front bottom of the car (for the radiator/coolant's sake?). Placing the sensor in that location would seem to explain the "high" readings we've all observed. Temperature over concrete/asphalt will generally be higher close to the surface. Test this by standing over your asphalt driveway on a sunny day then stepping onto you lawn; cooler? Even when travelling at speed (aspirating the sensor) the temperature will show a higher reading close to the ground because asphalt/concrete is a good radiator of converted short-wave solar radiation (to long-wave radiation) and re-radiated back into the atmosphere. The closer to the radiating source (the ground) the "hotter" the air will be. In a macro view this is what urban areas experience as "heat island effect."

    I've come to just subtract a few degrees from the screen reading. Your "mileage may vary" as the amount of adjustment to make.
     
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  11. rsomrek

    rsomrek Member

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    I should have added that in winter the temperature difference shouldn't be as noticeable - in-car readings should be close to the ambient outdoor temperature ( within a degree or two). The radiation effects are not as noticeable because the temperatures are low enough to cancel them out within several inches of the surface. (Snow will melt on your asphalt driveway but you're not going to cooking any eggs on it!)
     
  12. VT_EE

    VT_EE Active Member

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    Mine is usually high when parked, but goes down immediately to the correct temperature when I start driving. I'm curious where the sensor is located.
     
  13. fmcotton

    fmcotton Member

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    Have same issue here. Consistently Model 3 is showing 7- 10 digress off. We all should be reporting this as a bug. Hopefully they can fix via software update.
     
  14. tambam

    tambam Member

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    I’ve noticed mine is off by 7-15 degrees. Always high, but it is still summer.
     
  15. eprosenx

    eprosenx Active Member

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    I had always assumed ICE cars had the sensor in the air intake manifold. I figure inlet air temp is important to modern fuel map systems and so why not also use that sensor for the display in the cabin?

    I am wondering if Tesla’s are at a disadvantage here since their need for intake air is very limited (just enough for the radiator which is an integrated part of the cooling system).
     
  16. fmcotton

    fmcotton Member

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    I reported it on my Tesla account page and was already contacted by someone at Tesla asking for details: dates, time of day, difference in temp reading etc., They are investigating. I suggest anyone having this issue to report it to Tesla as well.
     
  17. outdoors

    outdoors Always roaming

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    More pressing issues to deal with for Tesla. I stick my finger to the wind after licking it. After that I realized it is a car not a thermometer. Some might say . It should be right, because it should be. It's a Tesla. Other say it should tell me when my left cheek is cold or warm.


    All I care is that the car after leaving it for 4 nights in the midst of knowhere that it works.. It does. Started at 77%.
    Ended up at 78% .
     
  18. UtahIsRad

    UtahIsRad Member

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    I really didn’t care too much about this during the mild fall (got the car end of Sept), but now in the winter it’s kind of an issue. For example. I drive up to the mountain to ski with my young kids and the car says it’s 26F outside when it’s really closer to 12F. That’s a pretty massive error.

    Classically, I’ve always been able to check the temp in the car to gauge how best to dress the kids, especially when putting them in lessons where they can’t just adjust clothing if it’s wrong. So now, I have to take a few minutes and check weather stations in the area on my phone.

    Annoying when a $.10 part should be able to do this well and every car I’ve had since ‘03 was much more accurate. It almost seems stuck at 26-28F, but then every once in a while it will show a more accurate temp. Where is the sensor located?
     
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  19. Raphiki

    Raphiki New Member

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    I've had many less expensive ICE cars with more accurate thermometers. This should be an easy fix for Tesla - probably an adjustment or software update. Mine always reads at least +4. Ridiculous in a car at this price point.
     
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  20. puckpurnell

    puckpurnell Member

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    Agree. Mine is usually high by 2-3°C.
     

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