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Can Gas loose its Octane rating

2198 Views 6 Replies 7 Participants Last post by  spaceman
I often wonder when I pull up to the gas pump and turn on the 93 octane. Seeing as though most of the cars pulling in buy the 87 or 89 octane - I wonder how old the gas in the 93 tank really is ? So - does anybody know if gas can loose its octane rating and if so what is a snowmobiler to do if he wishes to get his gas at the local gas pumps? Can I tell if the 93 is really 93 other than watching my piston melt!
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no way to tell. If it's a busy station don't worry. But if they don't get much traffic be cautioned. I don't think it realy losses octane rating, just gets yellow and smelly and doesn't burn well. But I could be wrong. If anything put in some performance improver or octane boost.

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I'm thinking that if the station isn't selling much 93 octane gas, that they will probably stop selling it so consumers don't get old gas. Just my thoughts though.

Trees don't make the greatest brakes...
Yes the gas can and does lose its octane rating. But as bigwilly says if they dont sell much then they dont keep it around. Well something to that degree. If they have a 500 gallon underground tank and they dont sell very much of it, then they only put 250 gallons in there, so they dont have to worry about having old gas. I believe it takes about 6 weeks for gas to begin to lose its octane, but that shouldnt affect any gas station much. Be surprised to learn that there are quite a few cars out there that REQUIRE the higher octane. Caddy's are a perfect example. So the High octane gas does get bought, but just not as frequently as the regular. I would say that you dont have anything to worry about.

Polaris is my way out - Other people just use a door.
yes old gas does loose its octane as it sits so dont pour gas into your machine until your ready to run it!, i have a bunch of cars and motorcycles in storage, and i just put a gallon in at a time when im gonna run them so my gas always stays fresh, old gas just plays havoc with a engine, i dont keep any fuel in my sled, who knows when we might get snow again in PA. i find this works best for me.

if its not a CAT, then it must be a dog!
I don't believe that gas will lose it's octane rating but it will change it's reed vapor pressure. As it sit's exposed to air or is in a fuel tank it can lose it vapor pressure. Gasoline is formulated for the region that it will be sold in meaning that winter fuel will have a higher reed vapor rating than summer fuel or fuel that is sold in hotter climates. The higher vapor pressure lets it vaporize in colder temps than fuel with a lower vapor pressure will.
What we call stale gas is fuel that will no longer vaporize and can be very hard to start an engine with. Octane will stay the same but all fuel can become stale. Just another reason to have fresh fuel in your tank.

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Sno-X, Beware, most gasoline improvers are'nt really boosting octane. Their Methanol or some other high volatility chemical that raise the flash point of the fuel. These kinds of things are fine for 4 strokes but are hell on a 2 stroke engine. Also, many more people burn 93 than you think.Most Euro-cars run it, and in the U.P. where I ride I think close to half the sleds are running it.

Mean Green Racing
Elyria, Ohio
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