So I was scrolling through Instagram not too long ago and I seen this:


And I wondered… in which instance would my 2007 Lexus IS350 burn gas more quickly, having my AC on or having my windows down? WAIT, no brainer right? Well here are my results:

Keep in mind I fill up at Shell only and get around 314 Approx Miles on my speedometer.

So for anyone who was curious about this controversy, don’t worry, I’ve ran some tests.

AC Full Blast for 3 weeks:
In every instance possible I had my AC on and let me tell you, my 314 approx miles would decrease insanely fast over time. As in, I would drive to work and home and noticed that by using the AC, I seen my gas go very fast and I find myself almost putting a full tank twice a week! I would also drive on the freeway to my school in LA and by the next work week I had to fill up already.

Windows Down 3 weeks:
Following my exact routine but instead having my windows down saved me a lot more gas. I know this probably seems like a no brainer but the amount of gas I saved rather than using my AC was ridiculous. I only had to put gas every week and 1/2 to 2 weeks

In summary: I’m sure we all know driving with the windows down saves more gas, but for anyone was curious about AC-Fuel consumption. Take it from me and use your AC wisely (if you’re worried about saving money/ fuel consumption of course).

 

I have read that it depends how fast you are going.. Low speed favours open windows and high speed favours AC and the crossover point is around 50mph depending on the car's design

 

The temperature delta matters too, as these have a variable volume pump (as I understand it).
Full fan high speed would matter vs low speeds.
Full cooling set to max compressor load, would increase the engine load and degrade the fuel mileage.

However, cooling set to auto on 76°F day, while the cabin is set to 73, the fan and compressor load will be minimal vs MAX AC and fan.

IMO the test done, doesn't represent typical conditions. You didn't mention the actal MPG for both tests, the outdoor temp, or the desired cooling, temp if it wasn't at max as described.

Obviously the entire AC will be working harder idling in traffic on a 90°F day than at highway speed the fan at the condenser will be running 100% too. There are a lot more factors.

Perhaps start with a windows up vs Windows down test as that alone could impact the aerodynamic drag. The AC is based on creature comfort 55° cabin vs 75° cabin and the ambient air temps.

Lastly, higher outdoor temps makes the air thinner for better fuel economy up to a point where the engine pulls back ignition advance...

 

I wouldn't drive on the freeway with my windows down to save gas lol It's super loud and windy. Though Lexus does have better control of the wind so it's not in your face.

I do like your experiment though; the internet is full of crap sometimes.