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Car ‘thermometers’ can’t be trusted on the hottest of days

Published: Jul. 28, 2021 at 10:30 AM CDT|Updated: Jul. 28, 2021 at 10:35 AM CDT
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OMAHA, Neb. (WOWT) - Quite often during hot stretches like the one we are in the middle of we’ll receive many viewer photos showing us the triple digit readings that show up on their dashboards and rear view mirrors.

Most of the time these will be much hotter than the official high temperature for the city of Omaha that day. This causes confusion but we’re here to explain to you why those car “thermometers” can’t be trusted on the hot days.

First of all, they aren’t technically thermometers. They’re actually called thermistors. Both measure temperature accurately but it is the position of that thermistor on the car itself that causes the wildly inaccurate readings on some hot days.

When you hear us talk about the high temperature for the day in the Omaha metro or any other location for that matter, we are measuring the temperature of the air. That is done in a very specific way. That temperature is taken about 6ft off the ground and in a shaded area, out of the direct impact of the suns rays and preferably over a grassy surface. This is done to reduce the impacts of surrounding objects influencing the temperature of that air as it passes over the thermometer. This gives us the truest reading of the air as possible and is used for official records.

Car thermistors on the other hand are often located behind the grill of your car or even under the bumper, at times no more than 2 to 3 feet above the ground.

Thermistor
Thermistor(WOWT)
Measuring
Measuring(WOWT)

With those thermistors located so low to the ground, they can be highly influenced by the heat that is absorbed and radiated by the road. Cement or asphalt can absorb quite a bit of solar radiation during the day, especially in a wide open area like a parking lot or section of interstate. That heat in turn will radiate off that surface and produce a much higher temp than the surrounding air and will often cause your thermistor and the read out in your car to be much higher than the air temperature itself. That is why they can’t be relied upon during the hot summer months. Poor location and too many things impacting that reading.

Road temp
Road temp(WOWT)

On the opposite end of the spectrum, than can be very useful in telling you what the temperature of the road is during the winter months and can help determine if ice formation is possible on the road you are traveling.

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