Originally Posted by kam327
Anybody have some REAL numbers for effect on mileage due to A/C use?
I noticed my last tank dropped about 2 mpg to around 31.5 for no apparent reason, and this tank looks to be even worse (computer currently reading about 30.5). This is after getting 33-34 over several tanks on my commute. The most likely culprit is increased A/C use - I used to use it only in the afternoon but started carpooling recently and I'm using A/C in the morning now too for the benefit of my passenger. But a 2-3mpg hit was much more than I was expecting.
The other main possibility is bad gas - I'll be switching stations next fill up to see if there's any effect.
I don't have concrete real-world numbers, unfortunately. But my experience has been just what you said: a 2 or 3 mpg hit. I think if you read up online you'll see that's roughly the conventional wisdom, too.
The dogma is something to the effect of driving with your windows down at 60 mph causes the same loss as running the a/c with the windows up. I do -not- believe this to be the case on the 2012 Focus. I think you're going to do better with the windows down through much higher speeds. And, if you can drive with the windows partially open instead of fully down, better still.
I get pretty kickass mileage in this car consistently, and others here have chalked it up to my driving style. And while I'll admit that's a big part of it, remember that I'm getting 38 mpg in this car when I would have gotten 24 at best in my OHV V6 Taurus. This car is more than 50% better. This is a pretty seriously efficiently vehicle for the power it makes considering it's not a diesel. There's still plenty more efficiency to gain, but compared to what we had available just 10 years ago, I think this is a pretty great car.