Here's why your car cabin temperature is usually wrong

Vehicles use thermistors rather than thermometers

By Samara Cokinos - Meteorologist

ORLANDO, Fla. - Every summer, pictures of car temperature readings flood social media. The pictures often show extreme heat, but are these readings accurate? 

The answer may surprise you, but most of the time they're not. 

Here's why. 

Cars are equipped with thermistors, not actual thermometers that have mercury in them. 

A thermistor measures temperature in a different way by detecting the change in electrical current that temperature can cause. 

That's fine and dandy, but it's all about location, location, location.

When placing a thermometer in your yard for an accurate reading of the air temperature, the ideal location is away from a building about 4 to 6 feet above the ground. It should sit above dirt or grass not pavement.

Also, you want the device to have it's own shelter to prevent direct and indirect sunlight from impacting the reading. The shelter also has to have good air flow to give a more accurate reading.

Keep in mind if the thermometer is in the shade of a tree, it will be a little cooler. If it's too close to a building or pavement the reading will be warmer. These things have a tendency to absorb and retain heat longer than the ground does. 

So, back to the thermistor. 

The placement is very close to the pavement and it's surrounded by the car, which is a hunk of metal.

During the day, the sun heats the pavement and the car more than the air. The result is the thermistor reads a hotter temperature than the actual air. 

Even in the evening, the heat from the road will cause the reading to be a little warmer, because it takes a while for the asphalt to let go of that built up of heat. 

At night and on a cloudy day, the dashboard temperature reading will be a little closer to the actual air temperature due to the lack of direct sunlight. 

Despite the difference, it's still fun to see what different dashboards across Central Florida have to say about the heat.  

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