Hello,

Just a quick question. How much does driving with the AC on impact overall MPG?

I had always thought it was more economical to drive with the windows open and AC off; however, I recently read that isn't necessarily the case, particularly at highway speeds.

Thanks,

Michael

2009 Moonlight G37S w 6mt

 

Minimal at best. Not enough for you to notice.

 

im so paranoid that im going significantly slower with it on. i too feel as though my gas goes through much more quickly its so sad im riddled with anxiety

 

An alternate question.. how much HP does AC steal from your wheels?

 

I read somewhere like 16% less with the A/C on

 

Below 60 km per hour, it's more efficient to drive with windows down. Above that, aerodynamic drag from having the windows open is more significant. However, having said this, the difference is minute, and it also depends on the baseline drag coefficient of your car. If you're driving a truck and your drag goes from 0.5 to 0.55, that's 10%. Our cars have a drag of 0.3. From that to 0.35 is a 17% increase in drag. Keep in mind also that fuel efficiency is not just dependent on drag. Stuff like drivetrain loss (~20%) is constant, and probably accounts for much more energy loss than drag.

 

Just enjoy your ac. If you want fuel economy buy a Nissan versa.

 

I have a spreadsheet that currently has 161 tanks of gas logged (among other things).

I have logged the differences in mpg vs. modifications, as well as having a/c on/off for extended periods of time on the freeway with the windows up (but vents open).

Bottom line? What everybody said. It's negligible. I get more of a mpg difference by changing the way i drive (light on throttle, getting up to speed quicker, coasting where possible, etc.).