Filling Up Full Tank Adds Unnecessary Weight Thus Reduces Mpg.

[getnpsi]

i fill my tank because I'm actively modifying the newly aquired car and looking to get a baseline to pull results from. Once I hit a plateau, get bored, or broke and need that last 1/2 tank ill quit and just throw $20 in at a time. MPG's are a pretty direct indication of the health of your vehicle (if you arent extreme hypermiling at the time). Once in a while I'll fill tanks 2-3 times in a row in other cars to see if they are getting the same output from a year ago etc.

[PaleMelanesian]

I use the scangauge, calibrated over 10,000+ miles, to calculate the trip-level usage. It may not be 100% accurate, but it's pretty close!

[IndyIan]

Well, I have some anecdotal evidence at best that weight isn't a huge factor in mileage.
I borrowed my Dad's 03 F150 4x4 5.4L auto, to haul fence posts and rails weighing about 1500-2000lbs. I drove 30km to pick up the posts and 70km with them and for both trips averaged about 14.2L/100km using my uncalibrated scangauge. The truck weighs around 6000lbs so I increased this by 25% to 33%. I did notice that it glided better in neutral when loaded up. I did do more gliding though when I had the load on as the roads were better for it and it seemed more worthwhile.

I guess this doesn't prove anything but it's somehting to think about.
Ian

[Big Dave]

My tank is rated for 29 gallons. Diesel fuel weighs 7 lb.gallon. The difference between full and half-full is roughly a hundred pounds.

A hundred pound difference on a 8,000 lb truck ain't worth worrying about.

[nascarnation]

Originally Posted by MetroMPG

You could fill up, then siphon most of it out and keep it in jerry cans, adding it back to the tank as needed.

Or fill your gas cans, store them at home, and add enough gas to the vehicle each day for the expected mileage.
Sort of like race car "qualifying trim".

(if you were really going to do this on a consistent basis, you'd want some type of dry break fittings to avoid dumping hydrocarbons into the air every fillup.

[88CRX]

I fill up all the time from empty, because:

1) Gas gets more expensive every week. Except after summer. The way gas prices are better to just get as much as you can now.

2) I think it is a waste of time and gas going to the gas station 3x (1/4 tank) more often than needed. Even if you get paid minimum wage, 5 mintes each fill up waste 15 minutes. That's what? $2.

I have to add, Don't store large amounts of gas at home. Some one burned down there house last week.

Sorry, Both are not related highest mpg possible. But you gotta be practical.

[ttoyoda]

Or fill your gas cans, store them at home, and add enough gas to the vehicle each day for the expected mileage.

I did that for a while. While I was filling my 4 five-gallon gas cans, some nitwit at the gas station asked me if I was building a bomb.

[Warhawk626]

I'm sure you guys will argue with me..and I must be calculating something wrong BUT every time I go below 1/4 tank I get worse mileage. That is with every vehicle I have ever owned and ranges from carb'ed V8's to FI 6's and 4's . High miles to low miles, they all began to feel anemic and sometimes even hesitated and kinda chugged on takeoff. The most drastic difference was about 3 mpg.

[johnpr]

^^ we saw the same thing in the graphs earlier in this thread, maybe it is a common thing and better to fill at 1/4 tank?

as for building a bomb, gas (as a liquid) isnt explosive, its flammable, many people dont know the diference though, maybe you were making napalm though.... i have my cyber eye on you... j/k

i always fill completely that way i get an ~accurate calculation on my mpg

-john

[hal9999]

[EDIT: merged the following posts into this thread to keep the info together - Darin]

I don’t know if this tip was already suggested but I recommend filling up your gasoline tank only half full. This decreases the weight of your car.

Off course this makes only sense if you live near to a fuel station.