So the fuel knows what size engine it is going into? It only stays fresh when used in large engines?
Small fuel lines, small fuel pumps, small injectors or carburetors, mean smaller amounts of fuel, which means less time for fuel to begin to evaporate.
The primary way ethanol causes problems is that on dry rubber surfaces it actually begins to dry rot the rubber. So when the gas evaporates, the dry rubber with ethanol on it starts to break down. Seals, O-rings, diaphragms (fuel pump diaphragms are often paper thin rubber), and the interior of fuel lines. These tiny particles of deteriorated rubber are then floating around throughout the fuel system the next time the engine is run, which can cause blockages. And with enough time, the smallest parts can deteriorate to the point they no longer seal properly, or the blockage causes a lean condition, which is typically when we notice engine damage.
Additionally, the longer fuel sits, the more it takes on water, primarily through condensation, so it happens more frequently in fluctuating cold temperatures. When an internal combustion engine burns fuel with water in it, the fuel mixture is leaned out by the water (the water is displacing some fuel), causing a lean burn condition.
These issues were reduced with the introduction of ethanol resistant parts beginning with the automotive industry (engineers were working on this issue prior to ethanol-blended fuel being approved), and more recently in small engines, once ethanol resistant parts were adopted. This is why you now see labels that say things like “up to 15% ethanol fuel” on small engines in recent years. More recent outboards tend to use an injection system instead of a carburetor. The injection system is far more sealed from outside air than a carbureted system. Combined with the eventual use of ethanol-resistant parts in that industry, 4 stroke outboards have developed a reputation for reliability.
However, if you run ethanol-blended fuel in a small engine that is not made with ethanol resistant parts, or engines that use carburetors, those parts begin to deteriorate as soon as the ethanol is exposed to air. Snowmobiles operate in some of the worst conditions for fuel – often sit for long periods, fluctuating cold air, and they were some of the last engines to adopt ethanol resistant fuel systems. That is why the recommendation is to run only non-ethanol fuel in engines that might sit for more than 5 days. Fuel evaporation, especially in a carbureted system, can begin in 5 days. If you run the engine in less than 5 days, the fuel system is refilled with fuel, thereby keeping air out and preventing the ethanol from deteriorating rubber parts. This is why frequently run engines do better when ethanol is present.
Huntindave, I don’t know you, and I try to not make posts that offend folks here at IDO. I typically post only to offer help or contribute to a post (hence my low post count). Your posts in this thread directed at me appear to be nothing more than criticism, and certainly do not offer any assistance to the OP. I would welcome you to offer your own insight if you disagree with my recommendation.