Most riders stay on top of oil changes and chain maintenance. The fuel sitting in the tank gets less attention, which is understandable since it looks fine, smells fine, and doesn’t announce its problems until the engine does. The gas available at most pumps today contains ethanol, though. Ethanol behaves differently in a powersports engine than in a car, particularly when the vehicle is left standing for any stretch of time.
The overwhelming majority of gas sold in the US is E10, meaning it contains 10% ethanol blended into the gasoline. E15 is growing more common at the pump. Both blends work fine in cars that run regularly, but they create problems for engines that sit for long stretches.
The core issue is that ethanol is hygroscopic, meaning it actively pulls moisture from the surrounding air. In a car that gets used daily, this doesn’t have time to cause damage. In a motorcycle, ATV, or jet ski that spends weeks or months in a garage, it does. As ethanol absorbs water, the mixture can reach a point where it separates from the gasoline and sinks to the bottom. That layer of ethanol and water is what the fuel pickup draws from first. What follows is a predictable sequence of corrosion, poor performance, and eventually a vehicle that won’t start. By the time phase separation has progressed, the fuel in the tank often has a noticeably darker color and a sour, almost vinegary smell compared to fresh gas. Most owners encounter it for the first time when pulling a cover off something that sat through a full winter.
It comes down to usage. Cars run often enough that fuel cycles through before problems develop. A motorcycle or jet ski can sit with the same fuel for months, giving ethanol all the time it needs to do its work. On top of that, ethanol degrades rubber over time: fuel lines, gaskets, and diaphragms can soften or crack with prolonged exposure, particularly on anything built before ethanol blends were standard.
Carbureted engines take the brunt of it, since their small jets and passages clog easily when gasoline oxidizes and leaves behind residue. Even a relatively short storage period can leave enough buildup to disrupt the mixture and cause a rough idle or a no-start condition in spring. Riders who store a bike in October and pull it out in April are often surprised that a vehicle running perfectly at the end of the season won’t start at all six months later. The gasoline looked fine going in, which is part of why the connection between storage and failure isn’t always obvious the first time it happens. Fuel-injected systems handle it better, but they’re not immune either, especially when phase separation is involved.
Fuel stabilizer works by slowing oxidation, which is the process that turns good gas into the gum and varnish that coat your fuel system components. Gasoline starts degrading not long after it leaves the refinery, and without treatment it becomes stale within 30 to 60 days, sooner in warmer conditions. Adding it before the season ends prevents that process from progressing unchecked while the vehicle sits.
It’s worth being clear about what the stabilizer doesn’t do, though: it won’t reverse damage that has already occurred or make old gas fresh again. It’s a preventative measure, which means the time to add it is before the vehicle goes away for the season, not after pulling it out in the spring and wondering why it won’t run. If fuel has already degraded and left deposits behind, a carburetor cleaning is often the most direct way to get things working properly again.
Most stabilizers are rated for 12 to 24 months depending on the product and how it’s stored. Brands like Sta-Bil, PRI-G, and Seafoam each approach it a little differently. Some focus purely on oxidation prevention, while others include cleaning agents that help keep the system clear throughout the off-season. Using the correct dose matters too, since adding more than the recommended amount doesn’t extend protection and can introduce issues of its own.
The process itself is simple, but sequence matters. Follow these steps each time a vehicle goes into storage:
If ethanol-free gasoline is available in your area, often at marinas or select stations, it eliminates the moisture absorption problem entirely and stays stable longer than blended gas. It still benefits from a stabilizer over a long stretch, but without the ethanol in the mix, the phase separation risk is gone. The catch is that it isn’t always easy to find and typically costs more than regular gas, so most owners use it selectively rather than exclusively.
When pulling the vehicle out in spring, it’s worth checking the condition of the fuel before assuming it’s fine. Discolored gas, a sour smell, or a visible separation in the fuel are all signs the fuel has gone bad, and at that point draining and refilling is the better call. Putting degraded gasoline through a clean engine rarely ends without a repair bill attached.
Fuel doesn’t announce itself as a problem until the engine does. A little attention at the start and end of each year is enough to keep it from ever becoming one.
