Why your car's temperature reading is often higher than reality

Modern cars do not actually use thermometers to display the outside temperature. Instead, they are equipped with thermistors, a type of resistor whose resistance changes with temperature. While thermistors are generally accurate and inexpensive to produce, their placement in vehicles often leads to inflated temperature readings.

The primary issue lies in the thermistors' typical location behind the front grille. From this position, they predominantly measure the heat radiating from the ground and road surfaces. These surfaces absorb significant solar radiation and are consistently warmer than the air, especially on sunny days.

As a result, the temperature displayed on a car's dashboard can be up to five degrees Celsius higher than the actual ambient air temperature. This discrepancy is most noticeable on warm, sunny days. When the sun is not shining, the temperature reading tends to be more accurate.

Interestingly, a similar effect occurs during colder weather, though in reverse. The road surface can be colder than the air, leading to a displayed temperature that is a degree or two higher than reality. This can be beneficial, as the car's computer may provide earlier warnings about potential icy road conditions, typically activating around 3°C.