It’s summer, and a heat wave is sweeping across the United States, which means your car is probably a rolling oven.

According to Hannah Fry (@fryrsquared), a fluid dynamics expert with a Ph.D. and a knack for social media, there’s a surprisingly simple hack to cool your car down fast.

“That age-old dilemma of choosing between having a non-sweltering car or baffling a passerby because you look like a fool who doesn’t know how to use a door,” Fry jokes in the caption of her Instagram Reel, which has racked up over 6.5 million views.

Cool Your Car Down Fast

Fry swears by it and says she uses it herself. Other content creators on TikTok have shown similar tricks using windows on opposite sides to create airflow.

“This is the trick I continue to use,” Fry, a Cambridge University math professor, says. “It’s what my Ph.D is in: fluid dynamics.”

Here’s how it works: Open one of your car’s rear windows. Then, on the opposite side, rapidly open and close the front door. For example, if you roll down the window behind the driver’s seat, swing the passenger-side front door open and shut quickly multiple times.

The idea is to create airflow: the door movement forces the stale, stifling air out and pulls fresh and hopefully cooler air in.

“When you open and close the door, it sweeps out all the air already in the car,” Fry explains. That action creates a low-pressure zone that draws out the “hot, sweaty, horrible” air—via what she calls “bulk flow”—and replaces it with “nice, fresh, easy air” from outside.

Is This Legit?

While Motor1 hasn’t tested it, the science backs Fry up. Opening a window creates a path for air to enter or exit. Pair that with an open-and-close motion on the opposite side, and you’re enhancing airflow, creating a natural breeze that helps flush out hot air.

And it’s not just for cars. The same technique can help cool down rooms in your house.

According to Marvin Replacement, different window types ventilate differently: double-hung windows push hot air out, casement windows catch side breezes, and slider windows let you adjust airflow. Bay and bow windows offer even more ventilation thanks to their wide flanking panes.

Viewers Confirm Car Cooling Trick Works

Commenters said Fry’s trick could save them from a lifetime of sweltering in hot, stuffy cars.

“You’ve just improved my life more than you know Hannah,” one person wrote.

“This may be the best Reel I have ever seen,” another joked.

Some confirmed they’ve already been using the trick, just without the science.

“This is how I do it—change the air,” one said. “I may not know the science, but I know the sense of it.”

Electric car owners chimed in, too.

“Cool trick. Or just do it from the app,” a Tesla owner wrote. “Or set ‘cabin overheat protection’ mode so it never gets too hot in the first place.”

Others say it works in tiny rooms, too.

“I do this with my window and door in my tiny room,” one woman said. “Additionally I also take a towel and move it in giant circles vertically to drag the cool air and flush out the hot air. I play music and dance a lil.”

Another added, “Works with houses too! My husband stands at the back door to stop it slamming, while I stand at the front door wafting it open and closed! Really shifts all that stagnant, hot air!”

Sure, doing this in public might draw some stares, as Fry experienced. But fans say it’s worth it.

“Lol people look at me like I’m crazy but I don’t give a [expletive],” one commenter said.

Motor1 has reached out to Fry via email. We’ll be sure to update this if she responds.

 
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