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.
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.
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.
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.
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-i-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.
