1996 BMW Interior Temperature

The plot below shows the temperature inside my and a friend's car on a hot day. His car is a silver Audi A4 and mine is a dark green BMW 318ti. The Audi had a Dallas Semiconductor Thermochron hanging from the passenger-side visor out of direct sunlight. The BMW had two Thermochrons, one on the visor in the same location as on the Audi, the other taped to the center of the dashboard. The cars were in a parking lot near each other away from trees and other sources of shade. Both faced the same direction, roughly SSW.

The day started and ended clear but clouds formed during the midday resulting in the temperature fluctuations seen in the plot. The ambient temperature in the shade was measured with a fourth Thermochron about four miles away.

Thermochrons have an upper temperature limit of 185 deg F so the dashboard curve is clipped where it exceeded this temperature.

Car-to-car temperature comparison (7604 bytes)

My cell phone battery has a stated temperature limit of 140 deg F. Since I leave it in the glove box most of the time I was curious just how hot it gets in there. I've also been curious about the temperature in the truck. During the summer I ran another test with three Thermochrons placed strategically around the car's interior. One was placed in the aft drink holder on the center console. A second was in the glove box and a third was in the trunk. A Dallas Semiconductor Hygro iButton was used at home to record the outdoor temperature while the test was going on.

The following plot shows the four temperatures over the span of a week. As expected, the console saw the highest temperature, a bit over 150 deg F. The glove box was a close second. Although the extra thermal mass and lack of convection resulted in a smoother temperature history, the temperature still broke 140 deg F, basically right at the limit of my cell phone battery. The trunk was the coolest spot of all, never reaching 120 deg F.

Car interior temps (11,947 bytes)

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