I've noticed that since my last oil change, my 2008 Prius is averaging (according to it's own computer, not my calculations) 39-41 MPG by the time it's time to refill the tank. I purchased this car last summer, and while I've been hard pressed to get the EPA records, usually in the summer with the A/C running I could average 45-48 MPG. This reduction upsets me. I have recently moved, so I've changed mechanics and I've noticed that they completely filled the oil after the change (almost a month since the oil change it hits right at the full dot). I may also be (unknowingly) using an ethanol added fuel -- just saw today that it can affect fuel efficiency. Tires are from Firestone, they have approximately 20K miles on them (they were replaced when I purchased the car). Any other suggestions as to why I'm getting winter fuel efficiency mid-summer would be greatly appreciated. I don't expect to break 50, I tend to drive my Prius a bit faster than most.... and living in Ohio with allergies limits how often I drive with the windows down. I do usually set my climate control to 70 degrees, fresh air and medium on airflow. Currently the car is not parked in a garage. I'd love to get my 5MPG back!