Why your car temperature is wrong

- Have you ever started your car, looked at the thermometer and thought, 'Man, that weather guy was way off. It's like 10 degrees hotter than he said.' Word to the wise - don't trust the thermometer in your car. In fact, there's not even a thermometer in your car.

Here at FOX 2, temperatures inside many of our cars on Wednesday read 100 degrees. The official high temp, though, was 90 degrees. So, why the difference?

Cars don't have a thermometer inside. Instead, they have what's called a thermistor.

A thermistor measures the change in electrical current as a result of heat added or removed. They're cheap to make, so car manufacturers like putting them in cars.

Truth be told, they do a pretty good job, but here's why the numbers are always a little bit skewed -- the thermistor picks up the heat that radiates off the ground because many car manufacturers put them in the grill of the car.

So, when it's sitting in the grill of your car, the thermistor is not only picking up the air temperature but also the heat radiating off the ground, which can sometimes be up to 10 to 20 degrees warmer.

That's why your car will always show you a warmer temperature when it's not actually that hot.

There's a scientific reason for why the inside of your car is always hotter than the outside, too.

We experience what's called the Greenhouse Effect. The sunlight gets in through the windows and the heat stays in there because it doesn't have anywhere to radiate out.

If it's 90 degrees outside, within 10 minutes the inside of your car can be hotter than 100 degrees. After a half hour, it feels like 125 degrees -- and after an hour the inside temps are reaching 135 degrees. 

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