Approximately how long does it take for unleaded gasoline in the tank and fuel lines to become unusable in a car that is not being used? What causes this, and what can be done to prevent or remedy the issue?

UPDATE: The car that prompted this question ('96 Lincoln Mark VIII, parked for about 6-9 months without preparation) has started successfully. The engine really seems like it doesn't like the gas, but it runs.

  • 3
    I'm not sure if it is related, but I've had gas in a gerry can for ~6 months that will still start a fire just fine :)
    – alex
    Mar 8, 2011 at 4:49
  • Just a thought, when you store something with a motor ( rv, boat, car ect.), if your able to drain the tank and use it for your car or truck. Leave the tank dry for long storage. Don.t forget to empty the carburetor, if it has one.
    – user11026
    Jun 27, 2015 at 3:13

6 Answers 6


I left my Mazda Protege unused in my garage for over a year, and the fuel filter was clogged when I went to start it again. It started fine, but would not rev and was basically undriveable. I'm sure it wasn't great for the fuel injectors, too. Also, I once bought a motorcycle with 10 year old gas in the tank, and the bike wouldn't run at all. I could hear a cylinder occasionally fire, but the gas was totally unusable. I poured it into a metal bucket and lit it on fire. The carbs were very badly gummed up and clogged, too, and had to be torn apart and soaked in carb cleaner.

If you use STA-BIL you can store gas for over a year without issue. Just make sure you run the engine for a few minutes to circulate the STA-BIL through the car. Once gas goes slightly bad, you can still use it if you put a little (1 gallon) in an (almost) full tank of fresh gas. The stuff I pulled out of the motorcycle was much darker than normal, and smelled so bad that I didn't even consider using it in an engine.

If you're planning to store a vehicle for a very long time, it makes sense to spend the time to totally drain the fuel system. It's cheaper than replacing the fuel system, later on, due to dried up, gummy gas deposits.

Here is some info I found on the STA-BIL website:

Q: How long will STA-BIL Fuel Stabilizer keep fuel fresh?

A: For 12 months when mixed into fresh gasoline. Doubling the dosage will keep fuel fresh for up to 2 years.

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    So, what about a quadruple dose - will that get me four years? If I just fill my tank with straight STA-BIL, will it be good forever? ;-)
    – Iszi
    Oct 24, 2013 at 13:28
  • Marine stabil plugged up our carbs and fuel tanks.. bad stuff.
    – user9771
    Mar 15, 2015 at 18:15
  • I don't know that Marine STA-BIL is bad, but I followed a small engine mechanic's advice and stored my snowblower with the tank full of Marine STA-BIL treated fuel, and ended up having to have the carburetor replaced because it too difficult to clean. I won't be storing it that way anymore, and will drain and run empty. Dec 7, 2017 at 22:03
  • Why does the gasoline go bad? Dec 19, 2017 at 14:04

It really depends on the storage conditions, but The Straight Dope suggests a storage life of 6 months to a couple of years.

The biggest issue to worry about is that the gas degrades and leaves deposits or gums, particularly in sensitive areas like injectors or jets. Another issue is that if accumulation of water in the tank. If the tank is kept full, there is less space inside it to collect condensation, which can help decrease this effect, but it also depends on the humidity where the gas is stored.


For lawnmowers and power equipment, gasoline can go bad in as few as 30 days. Always drain your tank before winter or add a fuel stabilizer which will prolong your gasoline life up to 12 months.

  • 2
    Why are lawnmowers and power equipment so special that fuel deteriorates so quickly?
    – theUg
    Mar 15, 2013 at 13:04
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    @theUg My first guess would be due to the smaller tank the chemical reactions happen faster, proportionally speaking, than they would in a larger tank. Also, smaller engines probably have less tolerance for bad gas in general. Would be nice to see more detail added here to explain.
    – Iszi
    Oct 24, 2013 at 13:21
  • 1
    I cannot generalize, but what you say is not true with our lawnmower. It has sat in the shack September-May for each of the last 12 years, and it starts with no issues every May. Jun 22, 2016 at 5:45

Stabil is not recommended in ethanol blended fuels as it causes a chemical reaction corroding brass in carburetors and speeds up the process at which ethanol mix gas breaks down fuel lines in vehicles made 2006 or older. All auto gasoline in the US contains a 10% ethanol mix as of 2007.

A version of Stabil was released that was supposedly ethanol friendly but it in turn sped up the process of corrosion and breakdown in older vehicles. So, the best solution is to just drain your gas before you leave the vehicle parked for an extended period. Just about every car has a drain plug in the gas tank. Simply take the plug out and drain it. Of course, make sure to capture it in a container appropriate for gasoline storage so you can either use it in something else or have it disposed of properly.

Once the tank is drained turn your key to the key on/engine off position for 5 seconds then turn it off and repeat about 3 times. This will clear the fuel pump and most of the fuel line of any fuel.

  • 3
    I am curious how this applies to electric cars. My average commute can generally run purely off battery making it so I would rarely ever have to use gas unless I do a road trip (which is basically never). Do the same issues as a car not in use apply to the gas sitting in an electric car? Do I need to purposely drive the car to drain to keep the gas cycled? if so... How often?
    – ggiaquin16
    Aug 25, 2017 at 21:47
  • I would down vote this answer as it is completely false, but the author of it never registered. Do not believe what is in this answer as it is complete conjecture and hearsay about the product mentioned. It is designed to work with ethanol blended fuels up to E85. Jul 1, 2020 at 12:56

Here in the UK regular gas has 5-10% ethanol but I use Shell V-power which is 99 octane and ethanol free (and more expensive) with Briggs and Stratton preservative in full tanks in my old motorcycles over the winter. In my lawn mowers the same stuff works fine in regular gas. Full tanks stop them getting rusty.


You can use Mix - n - Go after you get the car out of storage or begin to drive it again. When you put it into storage, the ethanol starts separating within weeks. Lucas sells a new blend for storing cars. Make sure for any storage blend that you not only put the stuff in but that you run the car so that it gets into every single line and injector / carburetor.

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