I think the a/c does the same damage to MPGs as the heater does. In the mornings when the temperature is at 72-74 , take my kid to school and got consistently 52 MPG. In the afternoon when the temperature is 89-92 , the same drive and I'm getting 43-44 MPGs. I'll keep investigatingNice - your fuel efficiency should be amazing then! If you read some of the recent "MPG" postings, we're just recently starting to warm up to ~68F in the US; today is the first day of spring. U.S. winter temperatures were 32F and below. The cold temperature can cause a 10+ mpg difference over the same route, especially since the gas engine runs to warm up the cabin and recharge battery for other cold-weather accessories.