Climbing into a car that has been baking in the sun is its own special kind of misery. The steering wheel burns your hands. The seat belt buckle might actually leave a mark. And the air inside is somehow hotter than the air outside, which feels physically impossible until you realize a closed car is basically a greenhouse with wheels.

The Japanese door trick actually works. You have probably seen it online: roll down the passenger window, then open and close the driver’s door five or six times rapidly. It looks ridiculous. It also drops the interior temperature by about 15 degrees in thirty seconds. The pumping action forces superheated air out of the car — air that can reach 140°F or more on a sunny day.

Why It Works

The car interior heats up through the greenhouse effect: shortwave sunlight enters through the glass, gets absorbed by the seats and dashboard, and re-radiates as longwave heat that cannot escape back through the glass. When you pump the door, you are physically pushing that trapped hot air out and pulling cooler outside air in. A car holds about 100 cubic feet of air. Five door pumps can exchange most of it.

Combine this with a sunshade on the windshield (the single biggest source of heat gain) and you can keep the interior 20-30 degrees cooler than a completely unshaded car. I use the $10 reflective kind from the auto parts store. It is ugly but it works.

What About Remote Start?

Running the AC for five minutes before you get in is the luxury solution. But if your car does not have remote start, the door trick is free and immediate. Crack the windows an inch if you are parked somewhere safe — that alone keeps the interior about ten degrees lower. The hot air has somewhere to escape instead of building up pressure.

Yes, you look like a weirdo pumping your car door in a parking lot. You are also the one who is comfortable while everyone else is sweating onto their leather seats.