I took a 6 week trip that started in indiana, went through the southwest and then up the west coast. I kept pretty close track of my mileage and something I noticed was when I was in the hot air down south my mileage increased by quite a bit. I was getting my normal 23-24 until I got into texas and at the time the temp was a 100+ every day. I noticed my mpg was going up and it stayed the same until I got to california where the temps started getting a bit more normal. I drove a couple thousand miles over a 2 week period where the temps were over a 100 every day( but it was a dry heat
the average for my tanks during that time went to 28-29mpg, which is the best its ever done. the only thing I can attribute it to was the hot temps as nothing else changed. it would be nice if I could do that good all the time.