my question is regarding to fuel up when reaching 1/4 of the tank or let it run till it ask? on my older car i would fuel up right about 1/4 of fuel left.. but i used medium and was told it was better to do this so pistons would stay cleaner.. now im wondering if i should do the same with my G or let it run till it ask for gas?
any personal opinions are much appreciated.

 

the G is a required 91+ octane, so in your words you would need for it to be BEST/HIGHEST and you need to do this so your engine will not ping/knock.

the inside of the gas cap states something similar along those lines.

 

I think what you're asking is when to refill your tank, is this correct? There's no actual "true or correct" time. I typically refuel at 1/2 tank for 2 reasons: 1) I have 2 kids and a wife I love, if there is ever an emergency the last worry I want is to have to fuel up to get to them (that would be a loss of precious minutes); and, 2) there is some information that indicates that as your gas tank has less fuel (especially <1/4), you tend to get less mpg since vapors are more prevalent (but I could be wrong on this one).

With respect to the octane rating, my manual recommends 91 (it does not require it) and where I usually live (Rio de Jeneiro) it's hard to sometimes find stations with >87 or 90. The same is true in many countries around the world where one can only find 87. I usually put in 89-91, depending on where I am. When in the US (currently) I use 91, there is limited value in exceeding this rating.

Good luck and I hope this helps.

 

i always fill my tank when the LOW FUEL light illuminates!

91 isn't required. Typically, 89 is the minimum you can run for NA G35s. I know with 87 my car would ping/knock a bit.

If you're at high altitude, you can run lower octane - say 87.

 

^ +1

 

I have a very bad habit of running my tank well below the empty line every time. I haven't run out of gas yet, usually get around 360-400miles per tank. Not sure about the fuel tank design on our cars, but it's usually not good for the fuel pump to run on empty all the time since it is kept cool when submerged in gas. I'm at over 100k miles with no probs so far though.

One of my new years resolution is to refill when the light comes on.

 

If I fill up when my fuel light comes on, the car will only hold 14 gallons, which means I had 6 gallons left. I usually trip the odometer so that I know how far I've gone on a tank. When I've gone about 320 miles, I start looking for a gas station, and I still rarely have to get more than 16 gallons.

 

I've been filling up about 25-30 miles after the light comes on. The needle is not quite all the way on the empty line yet. I get 370 miles a tank, and it takes around 17-17.5 to fill it. 21.3 average mph in city (small city, not as bad stop & go as So Cal).

The fuel loss from vaporization posted above isn't really a factor, as it doesn't sit around enough to loose a measurable amount (and it would experience vapor loss at all fuel levels anyway).

I like the fact that for the 2nd half of my tank, my car is 45+ pounds lighter than when the tank is full, so mileage goes up (small, but helps)