Wondering if any of you had any thoughts about something I noticed with my car thermometer recently. On 2 occasions, I got the impression that it indicated a higher outside temperature in an open-air parking deck, than when I had exited the deck. I wondered if that was caused buy how the thermometer worked, or whether for some reason the deck was warmer than the outside air.
We live in Chicago, where it has been a tad chilly lately. Both our cars have LCD thermometers. Both instances I describe involved a 1 yr old Integra.
A week ago we drove to a mall and parked in the deck. About an hour and a half later, we returned to the car. When we got in the car and started driving, I happened to notice the temp on the thermometer was dropping. I forget how much it dropped - maybe around 5 degrees. That seemed odd to me. I commented on it, and my wife and I discussed whether the garage had been heated in some way we didn’t notice, or whether there was some other reason the open-air deck would be warmer than the streets.
A few days later we went to a movie in a different location, and parked in a deck. After the movie, the thermometer read 19. By the time we had driven the 2-3 miles home, it had dropped to 10.
One thing we wondered was whether the thermometer did not adjust while the car was off. Maybe it was 19 when we drove to the movie, and 10 when we left. I do not know whether the temp dropped 9 degrees over that 2 hr period - I guess I could try to look it up. But the thermometers don’t seem to work that way. For example. If I am driving my car outside in the cold, and park in my (attached, unheated) garage, when I turn the car off, the thermometer will read the outside street temp. Say 20 degrees. But when I get into the car the next morning, as soon as I turn it on, the temp reads the garage temp - say 35. And then it will gradually fall degree by degree as I drive.
Any thoughts as to an explanation for what I’m seeing?
I would expect it to be warmer inside the parking deck. Even though it’s sides are exposed to the elements, I assume that you are parked in a covered portion of the deck, which should have some effect of trapping heat. Add to that, the heat from all of the cars parked there, I am not shocked that the temp inside the deck would be warmer than outside on the streets.
I imagine that is likely it. I did not appreciate that the heat from car engines would have such a significant effect, or that the deck would trap the heat. I thought the greatest impact would be blocking wind, which should not be reflected in the temp reading.
The thermometer reads on air pulled into the car’s air intake, below the front grill. For a car parked a parking structure that air is often protected from winds and heated by the sun. It can also be affected by residual heat from the car’s own engine radiating into a confined space.
According to this page, what you describe could be a couple things. The first is found in this quote:
“The system displays the last known temperature when starting the vehicle,” says Centennial College automotive professor Garrett Nalepka. “It may take some time and mileage to update to an accurate current reading.”After you start the car, you have to be driving more than 64.3 km/h (40 mph) for up to five minutes before the temperature gets updated, Nalepka says.”
So shutting the car off at 19º would cause it to show 19º again when you turn it on, and then after you start driving it updates to the actual 10º it really is… if your model car works that way.
Another possibility is that the thermometer is meant to be used while the vehicle is in motion. The linked article says that engine block heat doesn’t affect the temp reading in cars where the sensor is located in the front bumper of inside fender. That would be true when you’re driving and the air is freely circulating around. But when sitting stationary, that engine heat can sit still, radiate, and heat up the surroundings. When I stop my car after it’s been running at full temp for a while on top of snow, the next morning there will be a melted patch under the engine block. All that radiant heat has to go somewhere and if there’s enough of it to melt ice through a 6-inch buffer of open air, you can’t say some of it wont heat up the surround components around the engine and raise the temp a few degrees. It’s far more likely that your cars thermometer could have had it’s immediate surroundings warmed up slightly from the engine block than for the entire air mass in the parkade to be elevated 10º from trapped heat of some sort. Plus, you can feel the air is cold inside the parkade, so if your car thermometer says its warmer than you perceive it to be, that would indicate the sensor is probably not reading or displaying accurately.
Warm air rises … but the hood of your car prevents this … trapping the warm air … and the deck of the parking structure will also have this effect …
Try this experiment:
3] Park your rig outside one evening and open the hood the next morning compare the rig’s temperature read out with a separate thermometer outside your rig,
14] Park your rig outside one evening and leave the hood closed and then compare,
39] Park your rig in the garage, compare to the thermometer outside, and
82] Park your rig in the garage and stick a 100W light bulb burning underneath, compare to the thermometer outside.
I had a starter go out on a Chevy … the air temp was -25ºF so the starter was -25ºF … very difficult to handle … so I piled a few hay bales around, stuck a 100W light bulb underneath and the next day … although the air was still -25ºF … the starter itself was above 32ºF … thus no frostbite monkeying with the fool thing …
Not exactly sure how that would fit in with the example where I drive in 20 degrees, then pull into my 35 degree garage and immediately turn off the engine - certainly before the thermometer display changes. Next time I get in and start the car, it reads 35 degrees.
And thanks for the suggested experiment, watchwolf. Unfortunately, I doubt I will be conducting a detailed inquiry. I mean, I found it curious, but I wasn’t THAT interested! I do recall, however, when I had a classic (well - OLD, anyway!) car, I discussed garages and learned how much heat a single light-bulb could emit.
Thanks for the responses all.
Another thing I wondered - why does the temp reading change 1 degree at a time? I understand that would be the case in a standard fluid thermometer. But why would a digital/electronic setup change gradually?
To avoid jitter it isn’t displaying instantaneous temperature.
It’s displaying something like a moving average of the last 10 minutes’ readings taken at 15 second intervals. The result is a number that’s laggy, but stable.
There are several fancier variations on this idea and I have no knowledge about the details of your particular car. But it’s a darn good bet something along these lines is what you’re seeing.
I do recall, however, when I had a classic (well - OLD, anyway!) car, I discussed garages and learned how much heat a single light-bulb could emit.