i read on one of these threads that if you keep you tank at least half full you can see more milage from your gas. well i began testing this a few tanks back and its true. DUH. i dont have a evic so i use trip selection on my cpu. i was getting around 14 miles to the gallon average. what i did was fill up and clear my trip to zero. on a quarter tank i was getting around 100 miles. after that i would only get 135 more miles out of 3 quarters tank. i didnt get it either. but less room for gas to vaporize = better gas milage. so now when i hit 100 miles on the trip i fill it back up. this is equal to 4.5 gallons in my tank. 20.00 dollars. give or take. if i add it up thats 400 miles off a tank. compared to the 235 i had been getting from running it to empty. i also have been watching how i hit the pedal. i use bp gas only. just thought id share the info

The EVIC calculates gallons used by the amount of fuel the injectors put out, not by how much is used from the tank. So fuel vaporization in the tank would have nothing to do with it.

Your fuel gauge isn't an accurate scientific instrument. It's just there to giver the driver a heads up before he runs out of gas on the open road.

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2012 Jeep Wrangler Rubicon

I've been on www.GasSavers.org for a while now and I've haven't read anything about filling at half tank to reduce gas vapors. You would have to have a major vapor leak to make a MPG difference as large as yours and that would definitely set off your check engine light.

My vans have 25+ gallon tanks and I use a ScanGaugeII to constantly monitor my MPG. My finding show no truly measurable difference in MPG throughout the tank.

1999 Chevrolet Astro
1997 Chevrolet Astro

I'd like for you to add your Jeep to the Garage at GasSavers.org and log your tanks for us all to see. Who knows you maybe on to something.

Here's my wife's Jeep.

2002 Jeep Liberty

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Aaron

A vehicle isn't yours till you learn to wrench on it yourself.

2002 Jeep Liberty Sport (Eugene, I am the Passenger, And I ride and I ride.)
1999 Chev Astro 2WD (Green, Daily Driver)
1997 Chev Astro AWD (Grumpy "The Heep", $250 Rally Van, 335k miles, 2" lift, 31" tires)

ohh yeah, since your the one driving my jeep you would know. look dude. im useing my trip to alert me on my gas useage from a full tank. so when i refill it clearly says at the pump how much ive refilled from a full tank. i.e 4.5 gallons. this has nothing to do with an evic. and i do get 90-100 miles out of the first 4.5 gallons with a full tank. once more as i stated. i dont have an EVIC and im not talking about EVICs

Just to state that our fuel system is a sealed system.So with that being said even if your gas is vaporizing it's still trapped in your evap canister and is re-released into the engine to be burned.Keeping your vehicle's tank full as much as possible only nets better fuel range on older vehicles that do not have sealed fuel systems.

I'm merely asking for more testing and documentation. What happens if you go 1/2 tank, 3/4 tank? What were the driving conditions for the fuel usage? Inquiring minds want to know. I'd love for my wife's Jeep to consistently get 20-22mpg as you've stated your doing.

I know that kind of mileage in a Liberty is possible, we've done it on interstate runs (20.94 mpg over 317.4 miles @ 70 mph). You can review my wife's Gas Log and see where the mileage increased due to light hypermiling techniques and interstate usage.

_________________
Aaron

A vehicle isn't yours till you learn to wrench on it yourself.

2002 Jeep Liberty Sport (Eugene, I am the Passenger, And I ride and I ride.)
1999 Chev Astro 2WD (Green, Daily Driver)
1997 Chev Astro AWD (Grumpy "The Heep", $250 Rally Van, 335k miles, 2" lift, 31" tires)

No need to get hostile.

Unless your Jeep somehow violoates the laws of nature, this would apply to any vehicle. You gas tank is a sealed, pressurized system, so any volatilzed gas is limited because of the pressure. I'm not saying there isn't any.

Hell, for all I know you could be getting better mpg's, but your explaination isn't the reason why. The only thing that changes when you have less gas in the tank is the weight. Carrying less weight will increase you mpg's. So in a sealed, pressurized system, that uses a fuel pump to suck gas out of the tank, your explaination is invalid. Maybe it was windier one day, maybe the roads were wet, maybe the extra weight lowered you back end and decreased you wind resistance.

When's the last time you calibrated your odometer? Are you running stock size tires with no wear whatsoever? Are you using the same gas pump to fill up every time? Maybe one time you filled up, every single pump was busy at the same time causing the gas to flow out slower and you got you tank REALLY full. Maybe the next time you filled up you were the only one at the station and the gas flowed more quickly and cut off sooner, so you didn't get it as full. Maybe a fairy on a unicorn waved her magic wand and made the pump cut off quicker.

I run my Jeep down until it is sucking fumes. I'm averaging 17.1 mpg's in town (calculated both by the EVIC and by hand using trip miles and actual gallons put in) and 22.1 on the interstate.

The point is there are too many variables, and your equipment is too imprecise to conclude that it is an accurate measurement.

My argument wasn't with your conclusions, just your reasoning behind them.

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2012 Jeep Wrangler Rubicon

alright ill try this again. i use the same gas station all the time. BP. i fill it up. 18 gallons right.
i hit 3 quarters of a tank on my gas guage. my trip reads 90-100 miles.
i refill, same gas, same station. ammount of gas recieved, 4.25-4.75 gallons
this equals 20 mpg.
works for me.

and i also never said that the only reason was vaporizing. its just something i read about and included it in my writing. sorry for that. i was mearly letting people know what was working for me. thats all. have a nice day!

What were the driving conditions during the 100 miles?

_________________
Aaron

A vehicle isn't yours till you learn to wrench on it yourself.

2002 Jeep Liberty Sport (Eugene, I am the Passenger, And I ride and I ride.)
1999 Chev Astro 2WD (Green, Daily Driver)
1997 Chev Astro AWD (Grumpy "The Heep", $250 Rally Van, 335k miles, 2" lift, 31" tires)

well i live right by you. so we have the same weather.

Doh! I meant driving conditions. Was it an interstate run, cruising around town?

_________________
Aaron

A vehicle isn't yours till you learn to wrench on it yourself.

2002 Jeep Liberty Sport (Eugene, I am the Passenger, And I ride and I ride.)
1999 Chev Astro 2WD (Green, Daily Driver)
1997 Chev Astro AWD (Grumpy "The Heep", $250 Rally Van, 335k miles, 2" lift, 31" tires)

I did read about this in an email that was going around the theory being that the emptier the tank the more air for the fuel to vaporise in.

i have noticed bp gets better gas milege but i will have to try filling up at half a tank i do try to do that but so i dont feel like im spending so much every time i fill up iill have to chek the milege