Hello everyone, thought I would chime in today with something that is part PSA and part climate.
Many newer/modern cars include a display on the dash that is supposed to report "outside air temperature". My 2017 Subaru Impreza has this feature.
The issue that many people don't realize is that these sensors are often placed in such horrible locations that they cannot be trusted for anything with perhaps 1 exception (I'll get to the exception in a bit).
For instance, many car manufacturer's will put this sensor mounted behind the front bumper. Well, this does several things. First, it often means the sensor is reading radiant road temperature. Also, it means that when you are stopped at a traffic light, the sensor is reading radiant heat coming off your car's radiator.
Today is a perfect example of how inaccurate these sensor readings often are. Coming home, within the last mile to my house (which is dense housing and a lot of asphalt road), I saw the dash display report the outside air temp as 108 degrees F. According to DarkSky.net the forecast high near my house today is 95 degrees F. This means my car's sensor is off by a whopping 13 degrees!
So are these sensors good for anything? well, I can think of 1 thing they might be 'ok' for, which is determining a relative change in temperature over the course of a trip (like a commute), particularly if that trip has varied terrain and surroundings. Allow me to explain.
My daily work commute takes me from an asphalt and concrete urban heat island at my office building (which was reported to be 101 degrees when I left today despite the forecast high in that area being 95 degrees). From there I get on a freeway surrounded by farmland. I then transition to backroads surrounded by rice fields. Then I get into light density housing, then back into full blown urban.
So when I left the office the outside temperature was reported as 101 degrees on my dash. By the time I got to the backroads with the rice fields, the temperature was being reported as 93 degrees. That's a temperature change (or delta) of 8 degrees. This helps to illustrate (albeit in a crude manner) the effects of urban heat island vs rural.
As I transitioned back to populated housing areas (more concrete and asphalt) the temperature climbed back up to around 100 degrees, until finally near my house it peaked at 108. Again, the forecast high today is 95, NOT 108.
So, whenever someone wants to tell you that their car reported the temperature as XXX number, tell them to think twice. Those Outside Air Temperature sensors are placed worse than the 'certified' NOAA weather station thermometers are.
mad,
Often wondered and asked about those sensors for that very reason .
Only one person who I felt was truly knowledgeable of the situation convinced me that sensors located in the frontal area of the car actually were the source of temp readings.I couldnt fathom any location on a vehicle that might be "objective"and therefore assumed it was a GPS weather reading of some sort. This person however claimed to have had a car with the temp reading feature long before the remote sources were available,??Dunno. Maybe his car DID have a sensor back then??
John
Most likely it did.
As is the case with most car technologies and features, they started off as a luxury or upscale feature.
When I was in high school, my girlfriend's parents had a Chrysler Town and Country minivan with an Outside Air Temp dot matrix display. This was around 2003/2004 so the vehicle itself was a late 90's model or early 2000.
So here is a classic example of how and where the manufacturer's mount these temp sensors. This happens to be from a Subaru Outback.
What you can see right next to the sensor is the AC heat exchanger and behind that is the engine radiator.
Mad
Just the person I am looking for
I have a 2016 Dodge Ram 1500 4 X 4 hemi engine, approx. 25,000 miles
I drive in all kinds of fields on the farm with stuff brushing against the under side, mud, snow etc.
Very often when I start the engine [the engine starts and runs fine] but my gear shift is locked in park, or maybe not in park, just locked in position as park has to be given a little nudge to push it in park. I am not totally sure where the gear shift is locked. This happens maybe 1/4 of the time
No amount of wiggle the steering wheel or pushing, pulling anything etc changes a thing
I have to shut the engine off, then turn the key to accessories and then my gear shift is free
I then have to turn the key to off, then start engine and all is okay
I am terrified that some day my gear shift may not free up with all this nonsense
I have already had some kind of gear shift modular installed under warranty
I had 4 warranty re-calls stacked up but when I showed up at the dealership they said no I had 5 warranty claims
The 5th involved the gear shift
Is this a Chrysler thing
If you answer me this one then I got another thing that happens
Hope I did not scare you with my question
We need you on the site
"We need you on the site"
I concur with Wayne!
Wonderful post that's loaded with good information. Thanks for sharing.
We have a black asphalt driveway, so when my wifes car with the thermistor(I had never heard that term before today) on it is parked there, the readings can spike up pretty high.
The Weather Channel had an article on this not too long ago.
https://weather.com/science/weather-explainers/news/car-thermometer-thermistor-temperature-wrong
WG, let me do some reading on this to see if its a common problem perhaps with a clever or simple fix. I tend to be fairly car savvy and do all of my own maintenance and repairs.
Just so I'm clear and understanding your vehicle. I'm assuming its an automatic transmission and probably a column shift as opposed to a floor shift?
It almost sounds like an issue with the steering column/wheel lock jamming the shift mechanism, but again I'd like to do some reading first before I advise you.
Also, don't worry about scaring me off, especially when it comes to car questions. I should make sure you are aware though, I am not a car mechanic professionally, I'm actually a mechanical engineer. I just have a strong interest in cars as a hobby and enjoy doing my own repair work.
Mike,
That's an excellent summary article, thanks for posting the link.
I had to bite my tongue really hard a couple weeks ago when I overheard someone say that their car 'thermometer' was incredibly accurate at reporting outside temperature. I was at my fiancés parents house for dinner and they had a family friend there. I didn't want to cause a fuss, otherwise I would have made a point to explained why their statement was completely false.
And Wayne was thinking that he was going to get unlimited free advise from a certified auto mechanic indefinitely.
Actually, Wayne as a farmer for numerous decades with tons of equipment/machines that are in constant need of repairs is no stranger to diagnosing and working on issues like this himself.
Mike
You give me to much credit
In the old days when engines were simple [relatively speaking] I re-built engines because I could not afford to replace
An old barn was my work shop
Todays engines need a diagnostic computer, and not just any computer, but a computer for your specific engine, tranny etc
Then when we went to def additives that really messed us up
Yes we can work with the on board computer to let the machine steer itself, adjust the amount of chemical/acre, acres/hr and all sorts of wonderful things, such as a map showing where you have planted and the % skips or doubles. All good to know until it doesn't work, and the machine won't move an inch.
Our corn planter needs 5 hyd outlets on the tractor and at least three electric ports to operate
All this we understand but when a sensor malfunctions, maybe we can find it and maybe not
Our sprayer has 72 sensors on the boom alone, worth 18,000.00 to replace. The sensors cause a pulsing action, which is supposed to reduce drift. More than 12 MPH and the pulsing action does not keep up to the volume off water required so we travel 12 MPH with a 120' boom.
The final drives [wheels] have 1 electric motor/wheel each worth 18,000.00 as all 4 wheels drive the sprayer. We had to replace one this yr and sent the old one away to be rebuilt Now we have a spare motor. When spraying you can't wait for a rebuilt motor to be fixed 12 MPH and a 120'boom is a lot of acres or not a lot of acres if not moving.
Currently we spray 2 tanks of spray/day on the sweet corn because the ear worm is so bad. We just keep spraying two tanks/day every 5 days until it is harvested. We also have to go 1/2 speed to get as good a coverage as possible
That is just one example of many machines we need to keep working and why tile [dry soil] is so important in our operation
Have you ever had a flat tire and looked for the spare and the jack. Have you ever looked under the hood of your car??? One time I had a dickens of a time finding the oil stick.
Some times you just have to call for help
Mad
Yes: it is a 3 speed automatic steering column shifter, with cruise control
We do have the seat belt buzzer dis connected
When you get that figured out then tell me
Why do the wind shield wipers some times engage for one swipe only, when ever I use the left turn signal. Never happens when I make a right hand turn signal
The wiper controls operate from the right side and the turn signals operate from the left
There is no way I can accidently hit the wiper control when I use the left turn signal, which is on the left side of the steering wheel, opposite the wiper controls on the right side of the steering wheel
This happens maybe 1 in 20 turns
My niece has a chrysler make of car which does the same exact thing
The dealership quoted her 1100.00 to fix. They said it was a chrysler thing
We both just drive on.
When a dealer says "It's a Chrysler thing" that sounds like such a cop-out. That sounds like a manufacturer defect in my opinion and the customer is paying for poor design choices. But I digress.
I'm doing some reading on your shifter issue. If this was 'ye old days' (thinking of my 1964 Dodge Dart here), I would say there is an issue perhaps with the shift cables that go from the column to the transmission. However, this is modern times and few (if any at this point) shift mechanisms for automatic transmission actually have physical (cable) connections to the transmission.
That being said, I read on a Dodge truck forum where trucks built after 2010 have a shifter interlock solenoid. The solenoid acts as an additional safety so you can't shift out of park unless your foot is on the brake.
It's possible that the solenoid is sticking, or if you have noticed any trouble with your brake lights, perhaps your brake pedal switch is having issues. If the brake pedal switch is having issues, it might not be sending a good signal to the computer to release the shifter interlock solenoid.
Beyond that, assuming your truck does not have shift cables then this sounds like a mechanical fault of the shift mechanism in the column itself.
Regarding the wiper/turn signal issue. It is interesting that both your truck and your daughter's passenger car have the same issue across two different models.
If this was the days before CANBUS when manufacturers had to do point-to-point wiring harnesses (the massive wiring looms cars used to have), I would say that this sounds like a pinched or cross-shorted wire in the column somewhere.
This being the days of CANBUS...well, things get a bit more complicated. However, I did a google search and found this video that might be of use to you and your daughter.
Thanks for your generous comments related to Wayne's vehicle issues.
This is one topic that is way beyond my capacity to understand what's going on or learn from but you guys carry on.
However, the starting topic, vehicle thermistor's is one that any meteorologist would especially appreciate and gives me a great idea on a new thread!
Thanks for that!