The car in question is a 2004 Infiniti G35 sedan with manual transmssion. The revised EPA MPG ratings are 17/24. I purchased the car, used, in 12/2009 with 82K miles; it now has 91K.
I’ve gotten 25 MPG once on a single trip that was all highway driving. Pretty much every other fill up (with mostly city driving) has yielded between 13.5 and 15 MPG, and while I haven’t filled the tank in the last couple of weeks, judging by the gas gauge (which admittedly isn’t accurate, but it is consistent) it seems to be getting worse.
Here’s some relevant info:
[ul][li]Tires are in good condition and are kept at manufacturer-recommended inflation (30 PSI)[/li][li]I usually upshift at around 2500 RPM, downshift at around 1500, and I don’t ride the clutch[/li][li]I don’t have a lead foot[/li][li]Air filter is clean[/li][li]The “check engine” light has not come on since I purchased the car; in fact, the car has been 100% trouble-free[/li][/ul]
Additionally, I’ve driven probably over 150k miles with a manual transmission and haven’t had this problem with other cars I’ve owned (so I’m reasonably sure it’s not something I’m doing wrong, although I’m willing to listen to ideas).