Science‑backed fastest way to cool a parked car

Researchers demonstrated that the interior of a car can become up to eight degrees Celsius hotter than the outside due to the greenhouse effect, with temperatures sometimes exceeding 50 °C. Multiple cooling techniques were tested on a sun‑exposed vehicle. Leaving the engine running with the air‑conditioning on while stationary reduced the temperature by only about one degree per minute. Driving with the windows open for the first two minutes while the AC was on performed better, lowering the cabin temperature by roughly 2.5 °C per minute. The most rapid cooling was achieved by a method sometimes called the “Japanese method”: before entering, lower the passenger‑side window, then repeatedly slam the driver’s door five to six times. The rapid door movement creates a low‑pressure zone that draws hot air out through the open window, achieving a cooling rate of 3.6 °C per minute and bringing the cabin down to about 30 °C after twenty minutes of subsequent driving with the AC on. The technique works best when outside air is cooler, and frequent door slamming may wear hinges. Preventive steps such as parking in shade or using windshield sunshades also help reduce cabin heat.