Beat the summer heat: simple trick cools your car fast without air conditioner

By Phong Ngo July 10, 2025 | 09:21 pm PT

A fluid dynamics expert has shared a surprisingly simple trick, using airflow from rapidly opening and closing car doors, to quickly cool your parked car in during summer heatwave without air conditioning.

On a hot summer day, entering a parked car can feel like stepping into an oven. Due to the greenhouse effect, the temperature inside can easily be 10°C higher than the outside air, according to automotive air conditioning company AC Pro. While the car’s AC works to cool things down, you are left sweating for several minutes.

Hannah Fry, a fluid dynamics expert with a Ph.D. and a popular social media presence, has shared an easy-to-follow hack to speed up the process.

A car parked in the sun. Photo from Pexels

Here is how it works: Open a rear window, then rapidly open and close the front door on the opposite side. For example, if you roll down the window behind the driver’s seat, quickly open and shut the passenger-side front door. The technique creates airflow. The movement of the door forces out hot, stagnant air and draws in cooler, fresh air from outside. "When you open and close the door, it sweeps out all the air already in the car," explained Fry.

This action creates a low-pressure zone that pushes out the "hot, sweaty, horrible" air, replacing it with fresh air. Fry, a professor of mathematics at Cambridge University, added, "This is the trick I continue to use. It’s what my Ph.D. is in: fluid dynamics."

The trick has gained significant attention, with over 6.5 million views on Instagram, according to Motor1.

Commenters on her Instagram post were enthusiastic, with many saying the trick would save them from uncomfortable moments in overheated cars. One person commented, "You’ve just improved my life more than you know Hannah." Another said, "This may be the best Reel I have ever seen."

Some users shared they had been using the trick instinctively, though they had not known the science behind it. "This is how I do it, change the air," one wrote. "I may not know the science, but I know the sense of it."

Fry’s hack has also been demonstrated by other content creators on platforms like TikTok, who use similar techniques to create airflow.