Joe, I've used a lot of fuel that was around the same age as yours with no issue. Keeping it stored out of light and cap tight is important. If you develop funny business such as shutting off  considering your plug is good or the engine seems to be missing or running rough, you probably found your culprit. One thing about Sig is that I've found their plastic containers to develop splits and one day you find your bottles are empty or on their way to being empty.

I have used "old" fuel with no problems.  As long as it has not been contaminated (e.g. moisture) from repeated opening and closing it should be good.

I have had plastic fuel jugs split at the seam.  The split is mostly at the bottom but it can happen anywhere on the seam.  The problem might not be confined to Sig fuel jugs so it is a good idea to check all of them.  The split is sometimes very difficult to see.

If you have empty plastic jugs from Klotz or anything similar, keep one or two.  Same with empty gallon cans of lacquer thinner.  You will need them when you find a leaking jug.

You will get all sorts of responses.  It depends on storage container, temperature.

Old fuel sometimes coagulates, and the castor oil begins to form soft clumps.  These do not harm the engine, but will clog up the needle valve.

Before using old fuel, it is a good idea to pour it through a couple layers of paper coffee filters.

I have two unopened quarts of Sig Champion 5% that are around ten years old.  They have been stored in a cabinet in my indoor shop.  I plan to use it initially to break in an Aero Tiger 36 and OS LA 46. I also have a gallon of Sig Champion 15% from the same vintage that is about 3/4 full and stored in the same manner.  Are there any rules on fuel age and storage with regard to usefulness?

   As long as it doesn't get lots of light, should be fine. As far as I can tell, as long it is sealed, or was treated reasonably from an open can, and kept in the dark, you should be OK. Heat-cycling doesn't seem to hurt anything, although it can damage a plastic jug. I use 15% fuel almost exclusively at the NATs, I run about a gallon and a half, and usually have a half-gallon left over. It can sit half-used in a can in the back of my car for 3-4-5 years, from 35 to 150 degrees back and forth,  and pull it out, works just like before.

   I prefer metal cans to plastic bottles - if nothing else, they are opaque. Treating it properly when using it seems to require a "one way" fueling system, don't just open the top and dip a syringe tube into it, get some fittings for the cap like this:

https://store.flitetest.com/dubro-kwik-fill-fuel-can-fitting-dub807/p29357?msclkid=cd7b8152124114057534e13b1ec2675c&utm_source=bing&utm_medium=cpc&utm_campaign=FT%20-%20Shopping%20-%20PLA%20-%20INSTOCK%20-%20Desktop%20-%20Performance%20-%20Branded%20-%20NEW_GP&utm_term=4584757333941134&utm_content=new%20-%20gross_profit_lt_010

   This is plastic and aluminum, and will seal completely and not allow the fuel to "breathe", because it has an O-ring on the fuel outlet fitting. Put a filter in the up-line if you want, however, to date, I have never found *anything* in any quality fuel, and have run many gallons through as small as a 10-micron filter media and never had more than the tiniest fleck of debris from any respectable manufacturer (SIG, Powermaster, etc). Still put a filter in the airplane, of course, because even if the fuel is clean, the tank may not be and stuff can come in through the vent tubes

    Brett

A number of years ago (18 years), PowerMaster published five fact sheets on "Facts About Fuel".  Their Fact Sheet No. 5 was on "Storing Fuel for Maximum Shelf Life".  The following is from their two-page fact sheet:

"...one of the frequently asked questions is, 'What's the shelf life of fuel?'  The answer is both simple and easy:  Properly stored, model engine fuel will last almost indefinitely.  So....what constitutes 'properly stored'? ...  Contrary to many things you might have read or heard, just about the only thing that adversely affects model fuel is the absorption of moisture from the air.  Keep the air away from it, and your fuel will likely be potent longer that you are!  Methonol - the major ingredient in model fuel - is hygroscopic.  This means it's virtually 100% soluble in water, and absorbs moisture from the air like a vacuum cleaner sucking up dirt.

      [then there is a long discussion on keeping containers sealed so that the fuel cannot absorb moisture from the air.  Then, a short paragraph --]

"While it's true that the UV sunlight (or in fluorescent lights, for that matter) will cause pure nitromethane to deteriorate over time, it's our experience the once nitro is in solution and substantially diluted, the deteriorative effect is relatively minor. ...  While it certainly won't hurt anything to store fuel away from direct sunlight, it's our personal opinion that the adverse effect of sunlight on fuel under normal operating conditions is too little to worry about."

On the subject of PowerMaster Fact Sheets, these five fact sheets were two to three page affairs with the following titles:

No. 1  What's the oil content?
No. 2  Which oil is better - Synthetic or Castor?
No. 3  Nitromethane, the Mystery Ingredient?
No. 4  2-Stroke vs. 4-Stroke Fuels   Is There Really a Difference?
No. 5  Storing Fuel for Maximum Shelf Life

Some basic but interesting and useful stuff.  This was available from their website 18 years ago.

Keith

I had a chemist from work call his contact at DuPont Labs about this...maybe 30 yrs ago. He said the life is so long it isn't known yet and to keep it out of UV for the nitro.

I think he figured that it was actually leaner with the added rpm. I ain't buying the argument that fuel absorbs enough moisture in storage that it affects performance to a measurable amount.

   You are probably right on that one. But if you decide to try Joe's 10% water test, do it over high grass with and airplane you can easily repair.

    Brett

   You are probably right on that one. But if you decide to try Joe's 10% water test, do it over high grass with and airplane you can easily repair.

    Brett

Ha! Not an experiment I'm interested in trying.
I don't believe in abusing my Johnson.