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2010 Forester
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Discussion Starter #1
I have been reading advice on how to get the best gas mileage from your Subaru.
I just got my first Subaru last week and was wondering if you just filled up to 1/2 tank how much difference the 8 gal. would make in gas miles per gal. rather than running around with a full tank.
I do realize that you will be running double miles to get to a gas station.
 

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2015 Highlander AWD XLE 6AT
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4,255 Posts
Eight U.S. gallons of gasoline weighs ~50 lbs. By itself, it won't significantly affect your 3,200 lb+ car's fuel economy.

HTH,
Jim / crewzer
 

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2019 Crosstrek 2018 XT
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14,388 Posts
Waste of time. Just use less throttle. Thats where gas mileage goes south.
 

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2000 Forester
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75 Posts
I read that filling up when your tank is at halfway will give you a better value. Gasoline is volatile, the emptier your tank gets, the more space there is for it to turn into a gas, since gas is compressible. Gasoline in liquid form is not compressible (as with all liquids) so keeping it full may keep most of the gasoline you paid for in your tank. Not sure if gas tanks are equipped with a system to prevent this though.
 

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... Not sure if gas tanks are equipped with a system to prevent this though.
Not positive, but I think you'll get a Check Engine light if you had a loss of vapors. It's an EPA thing, and required on every car. That's why you get the CEL if the gas cap is not screwed on all the way, AFAIK.
 

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01 forester sport
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66 Posts
first of all congrats on your first subaru. i love my forester. i have a 01 sf sport 5m/t. if i fill up all the way i usually get about 340 to a tank. but if i fill up half way i usually get about 210 for about 8 gallons. i know that my tank is 15.9 gallons. im not too sure about other models and their tank size.
 

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2015 Highlander AWD XLE 6AT
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if i fill up all the way i usually get about 340 to a tank. but if i fill up half way i usually get about 210 for about 8 gallons.
Depending on the volume of a "fill up", and everything else being equal, these variations may yield similar results. For example, if ~2.9 gallons is left in the tank, a fill up would be 13 gallons. Over 340 miles, that's 26.15 mpg.

And, 210 miles / ~8 gallons = ~26.25 mpg.

Regards,
Jim / crewzer
 

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2010 FXT Limited 4EAT Sport Shift
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1,461 Posts
As the Car Talk guys say, "BO-0-0-GUS! not significant when compared to foot feed...fill it up!

I read that filling up when your tank is at halfway will give you a better value. Gasoline is volatile, the emptier your tank gets, the more space there is for it to turn into a gas, since gas is compressible. Gasoline in liquid form is not compressible (as with all liquids) so keeping it full may keep most of the gasoline you paid for in your tank. Not sure if gas tanks are equipped with a system to prevent this though.
 

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2008 Forester X Premium 5MT
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8,070 Posts
first of all congrats on your first subaru. i love my forester. i have a 01 sf sport 5m/t. if i fill up all the way i usually get about 340 to a tank. but if i fill up half way i usually get about 210 for about 8 gallons. i know that my tank is 15.9 gallons. im not too sure about other models and their tank size.
This probably has to do with the subaru gas gauge not being linear and the tunnel in the gas tank for the rear drive shaft to pass through, IE there is more room for fuel in the 1st half(top half) of the tank then the bottom 1/2.
 

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2010 FXT Limited 4EAT Sport Shift
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1,461 Posts
Another thought...running half full or less in a region where there is fairly significant temperature/humidity change, day to day, week to week, you're guaranteed to increase the likelyhood of water condensing in your tank...without additives, you'll soon see that there's NO advantage (short of forty pounds less weight, which WON"T make a difference in your fuel consumption either).
Much smarter for many reasons to 'run on the top half of your tank'....
-Quick
 
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