I just had my first 600 mile tank. 608.5 to be exact. Put 11.962 gallons back into it. 50.9 MPG calculated. The trip MPG only said 49.1. This is only the second tank. I don't think the dealer filled it all the way up on my first tank. We've had a real cold snap the last week or so. I'd say this tank the temps were at least 10 degrees colder than the first tank. Seems like people have been seeing a significant increase in mileage after the first oil change with Mobile 0w20. Between that and warmer temps this summer I will probably see better mileage in the coming months. Wow, what a neat car!