Lets talk of the validity of instrumentation
 

I've been in multiple vehicles with a mpg gauge stock and appears to only be affected by throttle position. I'm curious how accurate these gauges really are.

mpg causes a lot during driving and it's hard to test, from tank to tank using new techniques that are showing higher mpg is it making higher number at fill ups ie miles driven vs how much it takes to fill up the tank?

I've more or less hit a wall at about 40 high 30's depending on how late I am to work. but with the driving techniques I'm aware of and the car currently this is t he max I am capable of.

I don't use my UG as a way to tell the actual mpgs i am getting. Instead the avg mpg is just a point and then i have instant mpgs. yes it may not be the actual amount i am using at the moment but i know if my instant mpgs are high then the avg mpg goes up which means my gas mileage when i configure it at the pump is higher then normal if my avg according to the guage is higher.

Remember keep driving every1s vehicle is different whether it be altitude, terrain, etc.
your Hypermiling technique will get better to the point where you could be like palemelanesian pulling the highest numbers on the board with little mods

I intentionally have my UG read low to push myself harder and get a happy surprise at the pump.

...the end result is only as accurate as its inputs, ie: MILES from wheel revolutions and GALS from the ECU calculated fuel consumption.

As a general rule of the several cars I have owned (with instrumentation), only the 2002 Insight was close to accurate enough to trust. I once drove 650 plus miles on a little over 9.6 gallons of fuel.
The guage read 70.2 MPG and the fill showed it to be 70.18.

Every other car was optomistic by 2 plus MPG. The wifes Sorento, my 08 Altima Coupe and my current 2011 Ford Fiesta all were-are in the 2.5 MPG optomistic range. If I remember right the wifes 09 Rogue was somewhat closer but still optomistic.

regards
Mech

The most accurate instrumentation, and all you need is your odometer & gas station pump receipt, the average is the magic number.
They have fuel gauges for boats that work well.
Yamaha makes a nice add on to their instrument panel with a fuel flow meter.
It measures the fuel flow to the motors.

FWIW, our 2011 Cruze LTZ has consistently been about 4-6% too optimistic in its MPG readings since day one!

I trust no factory gauge, they are tuned to be more optimistic then true.

I use a SG and I keep the gauge pessimistic that way as it gets cold out I can be sure I get at least what the SG tells me. Today it was 10.8 gal and the SG though I used 10.9. that is close enough for me.

My factory gauge is dead on, within its spread (it moves in 0.3 mpg increments). Once I'm a few gallons into the tank, the dash and the Ultragauge are always in agreement and the pump receipt always ends up right there with them.

One place the car gauge is always off is DTE. For some reason the factory wants to trick you into not running the tank dry.

My only factory gauge is the combination of odometer and the "somewhere between F and 1/2" thingy. A well calibrated Scangauge is vital for knowing anything.