MEMPHIS, Tenn. (WMC)- You may be surprised to learn that the thermometer in your car isn’t a thermometer at all. It is actually a thermistor. A thermistor is a small device that measures temperature but it’s not the best representation of the outside air temperature.
Typically, temperature is measured with a thermometer. Most often, the liquid inside a thermometer is mercury which expands and rises to a certain value when heat is added, and contracts and falls to a lower value when heat is removed. A thermistor measures the change in electrical current as a result of heat added or removed but that is not the main problem.
The thermistor is not the problem in itself but it’s more the location of the device in the car. The thermistor is located behind the grill in the front of the car. This location exposes the thermistor to heat that is radiated from the surface of the road.
The asphalt pavement, any blacktop surface, absorb a significant amount of light and radiation and will emit the heat back out.
Car thermistors can give a more accurate reading when it comes to nighttime temperatures, when the heating from the sun is lost. They are also more accurate on a day when there are a lot of clouds and when you are traveling at a fast rate of speed due to the lack of influence from radiated heat.