I have an 05 G with about 1100 miles on it and have gotten 20, 22 and 22.22 mpg repectively out of my first 3 tanks of gas...that has been about a 70 hwy/30 city split. I have been very pleased. I'm only running 89% octane.

Try a different gas station...It might be bad gas.. I'm getting a little of 350 miles with a full tank on my new 05 and I have about 600 Miles on her now?

I'm hoping it's bad gas....I'll know soon enough!
Just a little note, I drove my brother's FX one time from PA back to NY, it was a 3 hour drive, 99% highway driving, consistently going 80-85mph, PLUS I had cruise control on most of the way. I filled up just before we left from where we were, and reset the average MPG gauge on it. After the 3 hours, I just barely broke 20mpg. I would figure as much for a car that size and weight (carrying 4 people), but I definately would expect better results in the G35

My sedan consistently gets about 24 MPG (80% highway). I have used Mobil1 5W/30 since 2200 miles. I plan on changing to this https://www.amsoil.com/storefront/tso.aspx
on the next change. I have their synthetic 75W/90 gear oil in the diff already. I use this stuff in my bikes and it definitely does what it says. And no, I dont sell it or know anyone that does, it just works.

I've got a coupe, but I'm averaging about 21 mpg with 2/3+ hwy and 1/3- city. Did a bit more freeway this last tank and got up to about 24 mpg.

Something definitely is wrong with your car (can't be explained by a break-in period). I'd discuss the issue with the dealer.

Heavy foot maybe, not worn in, and probably not full at your last fillup. Some of our G's are a bear to fill to the top.
C.

The car seems to get much better mileage when you keep it under/around 2500 rpm (70mph).

Cruise control also seems to make a big difference.

i get between 200-300 miles per tank. deffentailly depends on your driving habits. constantly bringing it to the redline will eat gas faster than you think.

you drove a FX 35 or 45 ? 45 is v8 engine, of cuz it will eat more gas. If its a FX35, i still not suprise with 20mpg, its a SUV, its more heavier than our G. Consider my Lexus RX 300(SUV) is about 20mpg also. My G35 sedan is about 18mpg, around 35% local and 65% highway, and it has 620 miles on it, i m hoping it will get btter after the brake in period and oil change

It's an FX35, not 45..
Here's another pic I took this morning. At this point I have 2 notches under half a tank, check out the stats!

OUCH! I would get that checked out. Something is definitely wrong, even on a brand new engine. Heck if you go on a trip you need a fuel truck to go with you.

Shoof,

Maybe you should keep a log of your miles travel and gas consumed, use this calculation independent of the NAV computer. I have a trip computer on my ML320 and it is always off by 1-2mpg as compared to my 'paper' tracking. My $0.02.

Shoof....

Someone put a top fuel funny car motor in your ride.

Kidding aside, you should definitely take this to the dealer and complain to them. I know that sometimes when a component of the emissions system heads south that it can really screw up your mileage (never seen it do so this bad though).

Just over 10k miles and for the life of the car I'm averaging just over 21 mpg with about 75% city driving.

I can't imagine what you guys are doing.

Well, maybe I can.

My 2004 6MT Sedan has approx. 15,000 miles now, has consistently been about 20 MPG average since about the 1,000 mile mark (was worse before then), averaging about 25% city/traffic and 75% open road (rural and semi-rural, still lots of stopping and starting at intersections/stopsigns).

I get average of 23 mpg over long distance freeway runs, averaging 80 MPH or more.

My $0.02