How to Use Fuel Stabilizer? | Prep Engines For Storage

The trick to keeping a lawnmower, generator, or classic car starting after months of sitting is treating the fuel before the problem starts. Gasoline degrades after about 30 days, leaving gum and varnish that clog carburetors. A fuel stabilizer like STA-BIL Storage extends that window dramatically, but only when you add it the right way.

When Should You Add Stabilizer?

Any time gasoline-powered equipment will sit unused for 30 days or longer, treat the fuel before storage. That covers the off-season for mowers and snowblowers, or a classic car parked for winter. STA-BIL Storage is marketed for exactly this situation, with the maker claiming fuel stays fresh for up to 24 months during storage.

One rule matters more than timing: always start with fresh fuel. Gold Eagle, the company behind STA-BIL, is explicit that the product works with fresh gasoline, not the stale half-tank already sitting in your equipment. Treat the fuel as you prepare for storage, not after the fuel has already turned.

The Correct Ratio For Gasoline

Measure the dose. Guessing the amount is the most common failure point, and AutoZone’s own guide stresses following the exact dosing instructions rather than eyeballing it. For STA-BIL Storage, the ratio is 1 oz (30 mL) per 2.5 gallons (9.5 L) of gasoline.

That same dose covers gas/oil mixtures and ethanol blends, so it works for chainsaws and two-stroke equipment. The other STA-BIL products use different ratios, so check the label: STA-BIL 360° Protection takes 1 oz per 5 gallons (19 L), while STA-BIL 360° Marine is more concentrated at 1 oz per 10 gallons (38 L).

Step-By-Step Treatment Process

Adding the stabilizer takes about five minutes and follows the same order every time:

• Measure the dose based on your tank size using the ratios above.
• Pour the stabilizer into the tank or a gas can before filling.
• Fill with fresh fuel. Adding stabilizer to an empty can first ensures it mixes thoroughly with the new gasoline.
• Run the engine for about 5 minutes so treated fuel reaches the carburetor and fuel lines, not just the tank.
• Top off the tank to about 95% full to reduce condensation that forms in the air space during storage, per Gold Eagle’s guidance.

After the engine runs and you’ve shut it off, storage can begin. The stabilized fuel sitting in the carburetor and lines is what protects the equipment, which is why the five-minute run matters so much.

What It Protects And What To Avoid

Gold Eagle lists gas cans, outdoor power equipment, classic automobiles, everyday vehicles, and boats as suitable applications. The product contains no alcohol, so it won’t attract moisture the way ethanol blends can. It’s safe for gasoline, gas/oil mixtures, and ethanol blends alike.

Don’t use STA-BIL Storage in diesel fuel. The safety documentation is blunt: “Do NOT use in diesel fuel.” There’s a separate stabilizer made for diesel, so check the label before pouring anything into a diesel tank.

Work outdoors or in a well-ventilated area, keep ignition sources away while pouring, and follow the precautions on the label. Then steer clear of the classic mistakes: treating old fuel, skipping the measurement, leaving the tank partially empty, or shutting the engine off before the treated fuel circulates.

For a look at our picks for treating two-stroke equipment, see our top two-stroke fuel stabilizer recommendations. That roundup tests the formulas best suited for chainsaws, trimmers, and other mixed-fuel engines.