SummaryGasoline starts going bad in as little as two months, then ruin your engine.
Damage can result
Gasoline starts going bad in as little as two months when open to the air, but can take 15 months.
Damage can result from using "bad" gasoline. As gasoline ages it begins to turn into varnish and forms a tar like gummy residue that can stick valves in the valve guides.
Very often the engine will develop a miss, if it runs at all. Black slime, most of the time, sticks the valve stem into the valve guide causing no damage to either of them, but the engine is unable to run properly.
Other times it is possible for the stuck valve to be hit by the piston which would result in catastrophic damage. This happens in " interference engines".
The refineries say
that gasoline really only has a shelf life of about 4 to 6 weeks from refiner to your gas tank.
This information is just as important for your lawn mower and snow blower, as it is for the gasoline you use in your vehicle.
Todays fuel goes bad quick:
Quite quickly, gasoline will lose some of the "light ends"(hydrocarbons that boil at ambient temperatures) when open to air, especially in a big tank which is half full of gas and half full of air.
These "light ends" evaporate in the intake manifold during starting thereby providing proper vapor to the combustion chamber. (the vapors are what burn)
Even more important is that when you lose these "light ends" it can contribute to lost octane quality and reduced power, which can be detrimental to performance.
Usually once this varnish starts to cause stuck valves, the engine will need disassembly and cleaning.
Sometimes using fuel stabilizer remedies this problem but you have to remember to add the stabilizer when the fuel is first purchased. Adding the stabilizer to "bad gas" will just stabilize the "bad gas" as "bad gas".
In the past many of us have filled our fuel tank up before storage, thinking that was the best thing to do to prevent condensation.
Now, as research proves, it would be best to use up as much fuel as possible before storage knowing that the fuel isn't going to be any good in the near future.