# Keeping 1/2+ tank saves fuel?

**URL:** <https://boards.straightdope.com/t/keeping-1-2-tank-saves-fuel/221483>\
**Category:** Factual Questions\
**Created:** [December 29, 2003, 12:12am UTC](https://boards.straightdope.com/t/keeping-1-2-tank-saves-fuel/221483 "2003-12-29T00:12:17Z")\
**Posts on this page:** 4\
**Page:** 2

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**Author:** ![CookingWithGas](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cookingwithgas/32/485_2.png) [@CookingWithGas](https://boards.straightdope.com/u/CookingWithGas)\
**Post date:** [December 31, 2003, 1:16am UTC](https://boards.straightdope.com/t/keeping-1-2-tank-saves-fuel/221483/21 "2003-12-31T01:16:44Z")

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A point I haven’t seen made is that if you are at 1/4 tank, and the space above the fuel is filled with fumes, filling the tank will push out the fumes (tank not air-tight while cap open for fueling) and you will lose whatever volume that amounted to in liquid fuel (see **KP** ’s estimate above).

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**Author:** ![KP](https://avatars.discourse-cdn.com/v4/letter/k/a9adbd/32.png) [@KP](https://boards.straightdope.com/u/KP)\
**Post date:** [December 31, 2003, 2:41am UTC](https://boards.straightdope.com/t/keeping-1-2-tank-saves-fuel/221483/22 "2003-12-31T02:41:47Z")

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> [@](#):
>
> Condensation from a low tank shouldn’t be a problem.

The problem with condensation isn’t potential corrosion. The problem with condensation is moisture in the gas, which can decrease the efficiency of combustion and proper metering of carburation or injection. It’s especially dreaded in cold climates, because it can freeze and keep your car from starting at all.

It’s particularly important to keep your tank topped up in the fall and spring when warmer, more humid days alternate with colder nights.

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**Author:** ![squeegee](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/squeegee/32/14537_2.png) [@squeegee](https://boards.straightdope.com/u/squeegee)\
**Post date:** [December 31, 2003, 5:26am UTC](https://boards.straightdope.com/t/keeping-1-2-tank-saves-fuel/221483/23 "2003-12-31T05:26:01Z")

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I’ve got a '92 BMW 325i, 109k miles, that’s been \<1/2 full 95% of it’s entire life. The performance seems fine, and the gas tank has not exploded nor (to my knowledge) corroded. Dunno if this has affected gas milage – I’ll let you know on my next '92 BMW. 🙂

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**Author:** ![Clothahump](https://avatars.discourse-cdn.com/v4/letter/c/51bf81/32.png) [@Clothahump](https://boards.straightdope.com/u/Clothahump)\
**Post date:** [December 31, 2003, 5:46am UTC](https://boards.straightdope.com/t/keeping-1-2-tank-saves-fuel/221483/24 "2003-12-31T05:46:58Z")

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I don’t buy the vaporization theory, but I will say that not letting the tank get below half full is a very good personal safety tip. You won’t be likely to run out of gas out in the boonies, or worse.

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