Dang, you must do a lot of city driving or have a real heavy foot!

 

I also average round 300 mi to the tank. I have a heavy right foot. But when i had my stock 17"s i got 400mi a couple of times

 

Haha, I wish. I am at about 125-130 on a half tank and at 225-250 when the light comes one. Of course 95% of my driving is stop/go city and very short trips.

 

I been looking and reading different threads and forums. It's been 2 years of over paying, fixing messing up and still learning from my mistakes. I have a 06' G35x 210k miles. I've had it since 2010. Got the car 2nd hand from a dealership In Va and Ilive in NYC. Mileage wise I know it did good when I first got it, But a few years ago it's been bad on mileage. I hear one guy saying he gets around 100 mile on a tank. I would guess I could be fewer miles than that. I am forced to do oil changes 1,500 because it burns out quick. And the oil leaks but nothing that drips or smell, I just see it around the engine at time. I spent alot of money try to diagnose it myself, buying spark plugs, air filters, oil catch can, cleaning the throttle body and maf. Idk whatelse to do. And now I'm seeing my gas gauge is floating now. It says full but after a few miles in it's at half a tank and if the light come on ,if there isnt a gas station within a mile its cutting off. I need help and advice. I dont have much money anymore due to Corona either. The most I have is a couple hundred to diagnose and fix.

 

Damn you brought this thread back from the dead! Probably would of been better off making a new thread that way you'd get more answers. I just so happened to stumble upon this thread in an attempt to see what the average mpg on a G35X is. Supposedly it's worse than the RWD Coupe and Sedan. From what I've been reading I'm actually faring fairly well. I have been averaging anywhere from 17mpg-20mpg. I have mostly highway miles though as I make a 120-150 mile round-trip 2-3 times a week. I just bought an 04 G35X 4 months ago, I put 93 octane in it all of the time. After I installed valve covers and gaskets, I also installed a Blox 5/16th plenum spacer as well as replacing the short ram air filter with a true cold air intake. I relocated the k&n cone filter to sit between the driver's side tire well and bumper. When I had the plenum apart to paint it I cleaned it really well, along with the throttle body, maf, and the upper intake manifold. I also ran a can of seafoam through the vacuum that goes into the plenum. I put half a can in the gas tank and the other half the through the vacuum. It burnt a lot of carbon and it made the idle a lot better it's not sitting at 650rpm with all of my mods. I also installed an oil catch can. I plugged the inlet that goes to the aftermarket intake tube. Ran a hose from bank 2 driver side valve cover behind the engine to the catch can on the passenger side. Then ran a hose from the pcv valve on bank 1 valve cover to the oil catch can. This catch can has 2 inlets and 1 outlet, so I have a closed system with the outlet going to the vacuum on the lower plenum. It's a baffled catch can and it's doing an excellent job catching the oil like it's designed too. It may not catch all of the oil vapors, but at least no oil is actually being sent back through the intake to be burned. I also changed the spark plugs to NGK Laser Platinums, got all 6 for $22 on ebay! Not bad considering they are normally $6-$8 per plug. Got 6 new coil packs as well on ebay for $45. I paid $55 for new valve covers w/ gaskets and hardware. I painted those as well along with the outside of the plenum spacer to camo it with the plenum. Paid $80 for that on ebay and I also went ahead and got a set of front vented cross drilled rotors w/ ceramic brake pads for only $55. Needless to say ebay is the ****, ppl can knock on purchasing parts on ebay. But I've been getting parts off ebay since 2002 with no issues whatsoever.
Anyways I drifted off subject there for a sec, forgive me. After installing everything I also went ahead and drained and filled the coolant, atf, transfer case and the front and rear diffs. Everything I did has made a huge difference with this car. It had 199,985 miles when I bought it in July. It now has 206k 3 months later in October. It's a night and day difference in how much better this car drives. It sounds way better now that it's breathing better. Has a deep throaty growl too it and man it really picks up in the high rpm range. It now accelerates way faster on the highway. Just the other day I was toying with a 2018 Honda Accord. Those are over 300hp, no way I should of dusted him. We were at a roll starting at 70mph. I floored it and was going 120+ within seconds. He was trying to catch up but couldn't. I'd slow down let him catch up while he was flooring it, drop it into 4th at 65 and accelerate back to 120+ easily. I really surprised him, considering it's a 16yr old car with a 200k+ engine, I must say that I'm really impressed myself.

I do admit that I have a led foot, the average speed limit here on the highway is 75mph. I'm often going 90-110 cruising, a lot of ppl actually drive that fast around here. I'm often getting passed up if I'm just cruising at 80. With me constantly pushing this car I'm still averaging 18mpg and I have a X which the awd is supposedly worse on gas mileage. So I recommend changing the plugs and coil packs it makes a huge difference. You said that you've already cleaned the maf and throttle body. Try cleaning out the plenum and upper intake manifold as well. Also run a can of seafoam through the vacuum going to the plenum. Make sure that you have someone in the car giving it throttle to insure that it won't hesitate and die on you. Then kill it as soon as it's done sucking in the seafoam. Let it sit and soak for a minimum of 10 minutes. Then crank her up and let the smoke session commence. You will have to rev it up a bit to get all that carbon burnt out. I wouldn't suggest driving it until the smoke starts to settle a bit. Depending on how dirty your intake, valves, pistons, etc are , will dictate how much smoke comes out as well as the intensity of the smoke. I've done this with every car that I've ever had. Only had one car that was so dirty when I first purchased it. That it looked like a house fire and I took it around the block to speed up the process and when I shifted to 2nd and 3rd gear it let out a puff of smoke so thick that I couldn't see any of the cars behind me. Talk about a smoke screen that **** was dense like fog. But everytime I've done this, every vehicle has responded well to seafoam. I really vouche and advocate for it, seafoam works wonders. You can also put some in the gas tank and it'll help clear any clogged injectors. Throw in an STP full fuel system additive as well it's like $8. Run that in a full tank and you'll notice it start driving better. I also had a bottle of Risolone Oil Treatment which replaces a quart of regular oil. If your car burns or consumes oil than it shouldn't be too hard to just top it off with that Risolone. I drove it with that in the engine for about 500 miles. The engine is a lot quieter now, in fact the radiator fans are the loudest thing you can hear at idle. Doing everything that I mentioned helped get my car from 14-15mpg gallon when I bought it. To 18mpg if I'm steadily mashing the gas and up to 20mpg whenever I'm just cruising. So to recap I recommend doing what I did, because I can definitely say that it indeed worked. It did at least for me so Risolone oil treatment, Seafoam, STP Full Fuel system cleaner, NGK Laser Platinums spark plugs, be coil packs, deep cleaning of the whole intake system, oh and I switched to Valvoline synthetic blend 10w40. I actually think it drives a lot better with a thicker oil weight. But that could also be all in my head due to everything I've done to it all at once. So it's hard to say for sure but everything combined has helped immensely with not only gas mileage but performance wise as well. It's like a whole different car. It also wouldn't hurt to check for any leaks around the evap system. Just get everything caught up maintenance wise. Change all of your fluids, it helps especially transmission and diff fluids. Get the fuel system cleaner by using the additives I mentioned. They are tried and true and all I've used for every vehicle I've owned. Good luck

 

The best way to calculate gas mileage is to fill up, set your odometer to zero, reset the vehicle computer and drive 300 miles on the interstate without stopping at 65 to 75 MPH
Refill the tank and divide the number of gallons into the number of miles traveled to obtain your MPG



Shown above is one of my many round trips from NJ to Florida with some local driving while in Florida

I'm on my third Infiniti over the past 15 years and I've seen similar results with all three vehicles including my current Q70. My best MPG on a single tank was over 27MPG
Do you maintain proper tire pressure and remove junk from your trunk?

 

Thanks Triple6lhp. That was a great and very detailed response. I am looking forward to doing this to my G.

 

Thanks Triple6lhp. That was a great and very detailed response. I am looking forward to doing this to my G.