Just found this interesting on a recent trip. Forgot to zero back after filling vehicle, and was curious how mileage is since my wife normally drives. Anyway, once done over next 50 plus miles going 65 mph with a/c on it was a bit over 42 mpg on dash. First time in 3 years I did that and was amazed . Normal daily driving still average 26 and trips with some stop go local about 36 mpg. So no complaints here.

 

this should answer your questions
https://acurazine.com/forums/2g-tsx-problems-fixes-145/how-many-mileage-you-get-full-tank-825029/