You winterized your mower or your pressure washer. You ran it dry, or maybe you added some fuel stabilizer and called it a day. Spring arrives, you pull the starter cord, and nothing. Or it sputters, coughs, and dies. We all know the feeling. The problem isn’t usually the machine itself. It’s the chemistry happening in the fuel tank while it sits, forgotten, in your shed.

Gasoline is not a stable substance. It begins to degrade almost immediately, a process called oxidation. This is especially true for the ethanol-blended fuel that dominates pumps today. Ethanol attracts water from the air, a phenomenon known as phase separation. The water and ethanol can drop to the bottom of your tank, forming a corrosive layer that directly attacks metal and plastic components. Meanwhile, the remaining gasoline forms gums and varnishes as its lighter components evaporate. These sticky residues clog the tiny passages in your carburetor’s jets and float bowl. This isn’t neglect; it’s simple chemistry working against you. For a clear breakdown of this process and its effects on equipment, the information at https://www.sta-bil.org/ lays it out in plain terms.

The damage is often cumulative and expensive. A simple carburetor clean might fix it one season. But repeated exposure to phase-separated fuel and varnish can corrode fuel lines, degrade rubber seals, and permanently ruin a carburetor. Replacing a carburetor on a lawn mower can cost half as much as a new, budget model. For a vintage tractor or a prized chainsaw, the parts and labor can be substantial.

The false security of a dry tank

Many of us were taught the best practice is to run the engine until it stalls, ensuring the carburetor is empty. This is good, but incomplete. It leaves the fuel tank empty, true. But it does nothing for the fuel that was in the lines or the microscopic residue coating the inside of the carburetor’s brass and aluminum. That thin film is still there, exposed to humid air, and it will oxidize and turn to varnish. An empty, dry tank is also a perfect environment for condensation to form on its inner walls, introducing water directly into the system. So while running dry is better than leaving stale fuel sloshing around, it’s not a complete shield. Your engine’s internals are still breathing in damp, oxygen-rich air for months.

Some hobbyists swear by using non-ethanol fuel for their seasonal equipment. This is a solid move, as pure gasoline is far more stable and doesn’t attract water. But it’s not a magic bullet. Even premium, ethanol-free gas will oxidize and degrade over time. It just takes longer. If your equipment sits for more than a few months, you’re still in a race against time and chemical breakdown. Finding pure gas can also be a chore and a premium expense, making it impractical for many.

A practical storage protocol

Stop thinking of storage as a single step. It’s a short procedure. The goal is to create a sealed, stabilized environment inside the entire fuel system. Here’s how I do it for my own equipment, from string trimmers to my old garden tractor.

  • First, add a fuel stabilizer to a nearly full gas can, not directly into the equipment. This ensures it mixes thoroughly. Shake the can well.
  • Fill the machine’s fuel tank to about 95% capacity with this treated, fresh fuel. A full tank leaves less air space, which means less room for moisture-laden air to condense and less oxygen to fuel the oxidation process.
  • Now, run the engine for five to ten minutes. This is the critical step everyone misses. You need to get that treated fuel out of the tank, through all the fuel lines, and into the carburetor’s float bowl and jets. You are purging the system of old fuel and coating every internal passage with stabilized, protective fuel.
  • Finally, shut it off. You can now safely store it. The entire fuel system—tank, lines, carburetor—is now filled with stabilized fuel, not air and corrosive residues.
  • Label everything. Put a piece of tape on the equipment with the date you stored it. On your gas can, mark when you bought the fuel and when you added stabilizer. Fuel has a useful life, even when treated.

This method takes an extra ten minutes compared to just dumping in an additive. But it addresses the entire system, not just the tank. The next time you go to start it, you should be pulling over fresh, viable fuel from the tank all the way to the cylinder. No sputtering. No cleaning. Just a clean start to the season, which is really all any of us want when the grass starts growing again.