19 gallon fuel tank?
 

For the first time, I was lazy and waited until my "stupid light" came on to get gas. It was flashing and showing that I had 20, then 10, and then zero miles left on my tank. Luckily, I finally hit a shell station.

Thing is, I filled it up and it only took 16.7 gallons. So either my tank really had 40+ miles left on it or my tank clicked full 2.3 gallons from actually being full.

What do you think, besides me being stupid for letting the tank get that empty in the first place.

Are you sure you completely filled your tank?

Were you driving 'aggressively' prior to getting gas? If the computer sees you driving with an avg mpg of 5, that 2.3 gallons isn't going to get you far.

Ya, the "range" is really only a calc based on the average mpg, rpm, etc.

There is only one way to find out, Mattie. Run it out in your driveway, which I understand is very bad for your fuel pump.

The reported "stupid light" mileage is NOT accurate by any means as it can fluctuate based on how steady your crusing is between its readings.

The most I've ever put in my Z is 18.48gal. So I'd say 19 is right. There have been times where I have pushed it too far...

Oh yeah? No check engine lights for running out of go-go juice?

never thrown a CEL, but I've probably put down 20-30 miles after all the dots were gone.

I'm sure Nissan also included a large buffer into that warning. It doesn't surprise me that there were a couple gallons left over.

There were some other posts where people ran out of gas thinking the later was the case. I think it really matters how you were driving prior to the fuel light going on. If you're cruising at 50 MPH in 6th, and toss it in third when the light goes on - I don't think you're going to make it far.

I don't pay much attention to the Miles Left thing, just the dots and the dummy light (if it gets that far). Once the last light is out you'd better be barely touching the pedal and rubber-necking for a station.

Most manufacturers have the light come on when there are at least 50 miles til empty. Usually 2 to 3 gallons.

There are few issues at play here. 1 is the actual value that the sender is putting out, 2 is the averaged value that the ECU is interpreting it to, and 3 is the dumbed down version that it decides to show you.

You can't see the value for 1 unless you intercept the voltage from the sender unit, but you can watch the value for 2 using an OBDII reader. The value changes significantly depending on how you are driving, and will creep up while you are stationary. The value for 3 seems to never go up unless you turn off the car, in which case it will reset to the value it gets from step 2.

As far as running out of fuel goes, you can drive down to the last drop if you drive like an old lady and avoid hills, but due to the tank design you in reality need a buffer of at least 3 gallons for average driving and 10 gallons for aggressive driving. The car seems to be calibrated so that it will read empty (no lights, 0 mile range) when you have approximately 2-3 gallons left in the tank.

then we'd be talkin a 20gal tank prob. i've had 2 or maybe even 3 fill ups over 18gal

Same thing with mine, completely normal. If you drive with some DRIVE, the computer freaks out. I generally have found (haven't really gotten that close), that there is approx. a 2 gallon safety margin built into the whole thing!

Yep, when I get down to two dots, the warning comes on. From there, the mileage till empty will jump all over the place depending on your "lead foot". The only time I have seen this warning to be of any value on Nissan vehicles is when you are cruising on the interstate and have the cruise control set, so the "consumption" isn't subject to "lead foot" and shifting gears. That said, the DTE (distance to empty) still showed " -----" , and I drove another twenty miles until I found a gas station. When the warning in the Z comes on at two dots on the gauge, if I fill up soon thereafter, it takes close to 17 gallons. Nissan is giving us a two gallon cushion.

John