Dont want to say it but their is plenty of threads talking about this subject and I'll save you some time. I too had very bad gas mialage and and I just switched my air filter and filled up my tires to the correct pressure and problem solved. I doubt its the air filter because it only has 27K miles but check it any ways to be on the safe side. But your tires are your best bet. You should also always check your oil. Heres a good thread https://g35driver.com/forums/g-spot/...-your-oil.html

 

Like i been saying, my oil change is new, my filter is new and my tire pressure is fine and im still getting horrible gas millage.. the car is mint and i drive it slow.. what else can i do.. should i reset the ECU?

 

I really don't think the ECU reset will help, there is something wrong. What's the gas like where you live, lots of ethanol in it, maybe?

 

Are you in NY city or state?

I assume NYC would be a lot of stop and go which would kill mpg. Also, does your car sit running a lot (warming up in the morning for instance)? That's time that would be zero miles per gallon.

I had a coworker that lives close to me with a G35. I asked him what mpg he got before I bought. I get about the same. Maybe you know someone around you driving about the same route. Ask them.

Oh not to rub it in, but I got 27 mpg on a roadtrip this weekend according to the navi. 300 miles all highway doing 65-80.

 

this is the first time i got 13MPG mostly city ,i got upset i can't remember if i drove the car hard, i had my sparks and air filter done recently, oil change every 1000k because of warranty, i know its winter but i never had it go lower than 15MPG

 

hey, since we are on this subject, i recently changed my staggerd OEM wheels (2003 coupe) for a 2006 sedan wheels because there was a problem with my wheels and i had to get it replaced for now. My old wheels gave me 20-21 MPG on freeway but after i got these new wheels ive been getting a lot less, like 15-16. My oil change is due but just barely so i dont think that is the problem. Anyone know if the decrease in size of my wheels have anything to do wiht a lower MPG? thanks ; ;

 

tires & wheels & pressure can make a big difference depeding on their weight width and wheel diameter, if u have wider & heavier wheels/tires that would increase rolling resistance, with smaller wheel & tire diameter that u have now you'll have higher RPMS going the same speed as with the original tires, check your tire pressure too should be no less than 32 i recommend 35psi

 

thanks maciejk, so basically i screwd myself into getting lower mpgs if everything else is in check?

 

Combined driving 25-27 MPG, if I am going on 95 or something and reset the onboard 'puter I can average 30-31 MPG.

I am not a heavy foot, air filter is super clean and tires are 35psi.

 

compare your current wheel & tire size to the original that you had with this calculator it'll tell you how much you are off http://www.miata.net/garage/tirecalc.html

 

yeah i am in NYC but still doesnt explain y im getting 12.5 mph... its disgusting i cant even afford the gas im fillin up every 2-3 days... and like i been sayin i do NOT drive the car hard at all... no one else is getting this millage i guess im guna take it in sometime this weekend

 

yeah your best bet is to take it in, and don't let them pull that it's normal bull, because its not unless you have forced induction or something. It sounds like something that might have gone wrong that is under warranty too.

Like i previously said the only time I got in the 12-14 mpg range was when I was driving around with both my o2 sensor out and that was all highway driving. The check engine light was on and the fumes smelled like the engine was burning extremely rich. I'd like to tell you it thats what it is because that is under warranty and a relatively easy fix at the stealership. But your ecu would have caught that and given you the check engine light

 

If the sensor fails completely so that its voltage is out of the acceptable range, then sure, the ECU would turn on the CEL. What if the sensor has some failure that leaves the voltage in the acceptable range, but horribly mistakes the O2 readings? The ECU probably has no way to detect this.

In any case, the original poster really should take the car for a diagnosis. If the dealer tells him nothing is wrong, maybe an experienced private mechanic could find the problem. G35's don't get great gas mileage, but 12-14 mpg is ridiculous and sounds like something's busted.

 

Wow! I have the same problem too!
Except I noticed: when I put the cheap Arco gas in (91 rating), I can get from SF,CA to Norwalk,CA on a tank of gas --NO BS!!
but when I'm driving local, I get really horrible mileage.. I average a little less then 100miles per 1/2 tank (200-220 mi/tank) .. my 02 sensors work fine-- but I swapped in test pipes for my cats.. I had an adapter welded so that the 02 sensor doesn't trip but it still produces horrible mileage anyways -shrug-..
you can always tune your car to run more lean to avoid burning so much gas.
Also, try cleaning up your engine. a good bottle of seafoam will do the trick!

 

wow 100 for a half a tank????? thats terrible! i usually get 165-185 for half a tank.

I used to use seafoam on my maxima, worked great!! especially the white corban build up smoke show. But im not sure id want to use it on the G35.