What size gas tank does a 04 G35 Coupe have??? The owerners manual says 20, but I don't see how that is right!? That is huge for one. The other thing that makes me think it's not, is the fact that I just got around 250 miles out of a full tank. I went to get gas and it was a little over empty and it only took 13.2 gallons roughly... 100 miles of the 250 were highway miles too! That means I'm getting roughly 13 miles to the gallon!? That's horrible!!! I might as well be driving a damn semi!!!