How long will a 5 gallon plastic containers of fuel stay fresh?
The API (American Petroleum Institute http://www.api.org/) recommends that gas is not stored for more than two years in an approved container without fuel stabilizer. There are stories on the internet (so they must be true!) of people using gas up to three years old without problems.
I can't verify that, but I have used gas over a year old in my 4-stroke lawnmower. Mix the old gas with some fresh gas (the more the better) and voila: now you have double the amount of crappy gas, and it works just fine.
About 3- 5 months in a sealed container, or 6 - 8 months with fuel stabilizer added. Recommended maximum storage is 1 year.
Here's yet another set of numbers. According to Exxon (emphasis mine):
In general, gasoline should be used within a month of purchase. When the engine will not be used for an extended period of time, it’s best to drain the fuel tank and then run the engine until it stalls. If you choose to store gasoline and follow proper storage guidelines, the gasoline can be expected to remain of good quality for at least six months.
Where "proper storage guidelines", according to that page, are, paraphrasing:
- In an approved container.
- Tightly sealed.
- At room temperature.
If you add a stabilizer, usually in the product description it says how long they're good for. Most seem to claim about a year.
After a modest research effort this is the only source I was able to find that verifiably came directly from a party involved in the gasoline industry.
Anecdotally, in my experience I don't generally have problems running generators off of gasoline stored for 3-4 months (I do this often), but I have had to flush / replace fuel lines on generators that have sat for a year or longer with fuel in them without being run.
I just used high octane premium gas to run a two stroke snow blower and a 4 stroke machine. The gas was in the red plastic gas cans and approximately 3 years old. I wasn't going to use it, but it snowed 18 inches and it was all I had on hand. It worked just fine. I don't recommend, but didn't have any troubles and iI will use the rest up rather than dispose of it.
At least one year. Gasoline over a year old is working ok in a BMW i3 REX. It's a hybrid that has a small engine range extender for when the electric charge is low. I hadn't used the gas since last October and wondered when it would be too old to be usable. (It's why I found this question.) I'm intentionally running off gas until the tank is empty so it can be refilled with new. It's not having any problem with it.