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For a low use vehicle, it was historically recommended to keep the gas tank full. The reasons were twofold:

  1. Prevent rust from forming in the metal gas tank
  2. Prevent water from forming in the gas tank due to evaporation and condensation

Nowadays, I wonder if either of those two rationales apply.

Are there any mainstream production vehicles that still use metal gas tanks? If not #1 is moot.

Given the advanced seals on current gas systems, is #2 still a factor? If so, why?

Overall, for a low use vehicle, I wonder if it is now advisable to keep the gas tank at 1/4 a tank or less. When I say "low use", I'm thinking of a vehicle that is driven 2-4 times per month for a total of about 100 miles per month. That way, when it is driven, and a little fuel is added, more of the older gasoline is replaced.

If a vehicle is driven 2-4 times per month for a total of about 100 miles per month, I don't think fuel additives are necessary.

For a low use vehicle (as defined above), in order to keep it healthy, how much gasoline should be kept in the tank?

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    Not sure about cars (but imagine it's similar), but you generally want to leave the tank as full as you can, with a stabilizer added in motorcycles. Leaving a full tank of gas eliminates the possibility of getting a lot of water in the tank, and stabilized fuel will last for plenty of time (1-2 years). The water, like you said, is bad for the rust potential. I was under the impression that gas tanks are always metal. I've never seen a non-metal tank, anyhow. – Shamtam Aug 19 '15 at 23:22
  • @Shamtam - Most vehicle tanks today are made out of some composite. It's lighter than metal so appeals to better gas mileage. – Pᴀᴜʟsᴛᴇʀ2 Aug 19 '15 at 23:47
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Another concern of leaving gasoline in a fuel tank is that it degrades. If left long enough, it will not burn as efficiently (if at all) and will cause many internal issues.

Gasoline in a fuel tank should be good for a minimum of six months before you need to start worrying about anything. Given you are driving the car 2-4 times a month for about 100 miles, you don't need to do anything special to keep anything in the car in good condition besides the typical maintenance (oil change, etc.).

You should be able to fill the gas tank to the top and just fill it up when needed without any treatments.

Check out this link for more information about low-use vehicles.

  • Thanks. That's what I was thinking, but I question if I was correct. At 100 miles/month that's roughly 3-5 gallons being used (depending on the vehicle). For a large 16-20 gallon tank, there is quite a bit of fuel that will be months old before long. But if gasoline fuel typically lasts a minimum of 6 months (after pumping it into the vehicle) without treatment, then maybe it's not a problem. – RockPaperLizard Aug 19 '15 at 23:54

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