How long is gas in a tank ok to use?

[SouthernGypsy]

Gas doesn't loose octane that fast though, I was a tactical driving and security specialist for years for the government and this is one of those facts they made us learn in class way back when and teach to new students today. The minimum standards in the US for what the industry refers to as storage stability rating says that in a sealed container with less than 5% vulume of air space present vs. volume of fuel and either air tight or with a proper sized vent for the container require that common pump gas must be able to last a minimum of 9 to 12 months with less than 1 point of octane loss and less than 1.2% degridation in overall formuation stability. That's at 9-12 months and even then you wouldn't get detonation with only 1 point of octane loss, not if your ski is tuned properly to begin with. If your getting detonation over that little of a drop then somethings wrong with the ski anyways. Most gas at the pumps can show almost 1 point of octane loss just brand to brand sometimes. Aside from the standards and what they thought us, a life of experiance restoring classic and collectable cars has only taught me from experiance that gas is actually more stable in storage than some people think. Most degredation from my experiance has more to do with the container (rust, scale, allows excess moisture in, etc) than it has to do with the gas itself degrading on it's own. The good news is that PWC's have plastic tanks and they don't rust, they don't scale, they don't let in too much moisture if you have the proper cap on and your vent lines are in good shape, and as long as you use good gas that's not contaminated in the first place (such as pouring out of another container that may have contaminents in it) then they generally store very well, especially if you keep them near-full.

[dorny119]

Old thread. But wow, SouthernGypsy seems like he knows his stuff. I have honestly never had any problems with fuel sitting in my tank for 5 months or so.