how long for fuel to go "bad"?

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May 25, 2009
fremont nebraska
The owners manuals to all of my outdoor power equipment bascailly say not to use fuel older then 30 days old. Just wondering if you guys think thats good advice, or are they playing it waaaay safe by using such a short time limit?
Originally Posted By: Silverado12
Mine sets 4 months (E-10) and never a problem. I'll start everything up and let idle for a while on a warm day during the winter, though.

Bad idea. You are creating fuel diluted oil and creating condensation in the engine which at idle will never boil off.
Never start a vehicle unless you plan on driving it. Starting an engine just to idle it means excessive wear.
Depends on the OPE. 2 cycle engines seem more sensitive. I have a flathead briggs on my riding mower that could run on anything. It's not uncommon for me to dump the 2cycle mix into that (which is then considerably dilluted in the tank, 200:1 or less of oil) after 60~90 days.
Old OPE doesn't like E 10. However,I have had less carb/dis-use troubles since I began dosing the engines with a little MMO.
Another discovery is Berryman's Chem-Tool. It is cheap and effective at cleaning out varnish and crud. It is a solvent, not a detergent, so I don't use it on a regular basis.

I started my snow blower, ran it until it ran steadily with the choke off. Then I shut the fuel off. I'm more concerned with the engine starting than I am with the engine's running.
The fuel for my outdoor power equipment is sometimes 6 months old and I don't have problems but I almost always add fuel stabilizer. My 2 cycle mix for the chainsaw and weedwacker sits the most, and definitely always gets a dose of fuel stabilizer when I mix it up. If it's warm weather and we're having plentiful rain I sometimes skip adding stabilizer for the riding mower & push mower.

The owner's manuals for my outdoor power equipment do state using fuel stabilizer is an effective and acceptable alternative, especially at end of season.

The 'time limit' really depends on a number of factors. The composition of the gasoline, the temperature, the degree of exposure to UV light, oxygen, iron, etc. way too complex to simply declare a 31 day limit.

I've been using the G-Oil stabilizer for a number of years even when we lived in SE Louisiana (plenty of heat in the detached garage) and it's been very effective for me and has been inexpensive at Walmart and Meijer.

It has a very distinctive bouquet. I use cheap disposable food handlers' gloves when I mess with it.
Looks like you have several stations that have non ethanol gas. Use it and don't worry. I keep 2 stroke gas for a year and do not have any sort of problem. I go through regular gas a lot more often but it could stay in a certain machine for up to a year. Again no problems.
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Nyogtha notes other factors then just time..... years ago I saw a temperature chart for gasoline oxidizing, jelling, varnishing, etc and it was VERY temperature dependent. Little aging happens during cold temperatures.

Likely the reason I have NEVER winterized a lawnmower in the last 50 years and they always start just perfect in the spring. Attempting the same thing with snowblowers....stored during summer of course....and the carburetor is always gummed up, splashing gas in it, running it at full choke for half an hour until it cleans up and can run without it still sometimes rebuilding it is necessary. Now, I carefully run snowblowers dry each spring to prevent the inevitable.
Here in hot and humid South Florida, "Rec-90" fuel with Sta-Bil lasts a year without trouble. I just found a 5 gallon plastic gas can that I filled with Rec-90 + Sta-Bil this time last year. Smelled perfect and ran perfectly.

However, pump gas with 10% ethanol goes bad rather rapidly, even with Sta-Bil. It's junk after 4 months.
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I let mine age to 6 months and always use stabilizer. Since I started using stabilizer I have had zero problems year-round with fuel. I always keep 20 gallons out back for OPE and genset standby.
Originally Posted By: Cujet

However, pump gas with 10% ethanol goes bad rather rapidly, even with Sta-Bil. It's junk after 4 months.
That's been my observations. My friend's boat(06 Yamaha 4 stroke 225) never ran right on Stabil treated E10 that was even a few months old. Once he started using E0 the issues stopped.
funny thing happened to me. Bought a used jetski 2 weeks ago. Had sat in this guys shady backyard in Minnesota for the last 5 years. 5 YEARS!!. I siphoned out the gas, was going to find a way to dispose of it. However, as I was siphoning I looked at it, was very clear and clean looking and it smelled pretty much like regular gas, maybe just gas that lost a bit of it's most volatile compounds. Got about 3 gallons and threw it in my RAV4 with about a 1/4 tank. Drove it to the gas station and filled up the rest of the way. Been running fine since. I have to believe that the state of old gas depends upon how tight the storage tank is. If it is tight, I truly believe a year is no big deal. If it leaks, it could go bad in a week.
Originally Posted By: Merkava_4
Fuel will go bad in 30 days if you don't use a preservative.

1 ounce of Sta-Bil for every 2-1/2 gallons does wonders.

Their marketing department should give out hefty bonuses this year for a job well done.
I don't buy it. If a tank is totally sealed, no air or water in, or out then how does it go bad? It doesn't and my 5 year old fuel proves it. There is not some chemical reaction happening unless there is something going in or out, like air. Fuel going bad in 30 days is an urban legend, IMO.
It doesn't. If your gas is going bad in 30 days you should invest in a decent gas can and stop using a five gal paint bucket with an old piece of tin as a lid.
I've found fuel to be fine after a year in a sealed can.
This was E10 as well.
Haven't been here for almost a year. Seems that the same questions are asked over and over. Can't recall how many times this discussion has been had and the same polarization of opinions.

Magic elixir advocates vs. no additives advocates. I'm of course with the latter. I've been leaving fuel in sealed plastic fuel cans for six or seven months at a time over winter. Each spring, I use that fuel to get my equipment running. Everything from two stroke outboards to four stroke riding mowers. Never a problem. However, as, one participant mentioned, temperature may play a role in how long fuel can be stored before deteriorating.

I know bush plane pilots who've cached 45 gallon drums of aviation fuel for well over a year up in the arctic. Keep the containers sealed and there shouldn't any issues.

It's not hard to determine if the fuel is bad. The smell of bad gas is hard not to notice. If it still smells like normal gasoline, it's fine.
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