Why Car Thermometers Always Seem ‘Inaccurate’ and Show It’s Colder Than it Actually Is

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As the chilling grip of winter tightens, the reliability of car thermometers during these frosty months often comes into question—and for good reason. As warnings of freezing temperatures and icy conditions are issued, morning routines start to include the need to warm the car up before leaving home. Yet many people get into their car just to see a surprisingly low temperature on the thermometer, feeling confused.

Inaccurate Thermometers

During colder days, drivers often notice disparities between their car’s temperature readings and those displayed on their phone’s weather applications. Brian Donegan, a meteorologist at weather.com, offered insight into this difference.

He explained that car thermometers often present higher temperatures than the actual ambient temperature, especially on warm summer days. He pointed out various reasons for this discrepancy, shedding light on why these readings may not align accurately with external weather conditions.

The Reason

Your car’s temperature reading isn’t what it seems. The so-called thermometer on your dashboard isn’t actually a thermometer at all, but a thermistor. Donegan explained that while a mercury thermometer measures temperature through mercury expansion, a thermistor gauges temperature by detecting changes in electrical current due to heat.

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However, the issue doesn’t lie with the thermistor itself; it’s more about its placement. Typically located behind the car’s grill, the thermistor gets exposed to re-radiated heat from the road surface, which can be significantly warmer than the actual air temperature. This discrepancy results in a reading that’s often much higher than the real outdoor temperature. Therefore, relying on more accurate sources like the Met Office app for forecasts might be a safer bet.