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How does a car’s outside thermometer work?
I’m curious, how does a car’s outside thermometer work? Shouldn’t the heat of the engine or wind chill make the reading inaccurate?
Jack Walsh · Updated on
Reviewed by Shannon Martin, Licensed Insurance Agent.
Those are great questions! Interestingly, cars use a thermistor, not a thermometer, to generate temperature readings.
Unlike thermometers, thermistors don’t use a liquid like mercury. They read the temperature by measuring the change in electric current as a result of heat added or taken away. In general, thermistors are small, cheap, and accurate, making them incredibly convenient in automobiles.
Thermistors are strategically placed to prevent the engine’s temperature from influencing the reading and are often found behind the grill but in front of the radiator or in mirror housings or fenders. Additionally, only living creatures experience wind chill, so the thermistor does not have to be shielded from wind to get an accurate reading.
While engine heat and wind won’t skew the temperature reading, reradiated heat from the road can cause inaccurate readings, which is why your car’s temperature reading may seem abnormally high if you’re parked on hot pavement.
Unfortunately, there is no way to avoid the influence of reradiated heat on the reading, but this should only inflate it by a few degrees—unless it is an incredibly sunny or hot day.
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