How to Store a Small Engine for Winter: Off-Season Fuel Checklist

The mower goes in the shed in October. The sled goes in the barn in April. Same problem on opposite calendars: a tank of gasoline sitting still for five or six months with nobody watching it.

Storing a small engine for winter is where the advice turns contradictory. One neighbor drains everything bone dry. Another fills the tank to the cap. The ATV manual says to run the engine for 20 minutes, and the chainsaw manual says nothing at all. This guide sorts out which of those steps earns its place, why fuel is the part that fails, and what each machine in the garage needs before the door closes on it.

What should you do with fuel before storing a small engine for winter?

Start with fresh gasoline, add a stabilizing fuel treatment that controls water, fill the tank, then run the engine for several minutes so the treated fuel reaches the carburetor or fuel rail. Briggs & Stratton recommends topping off the tank to help prevent moisture from condensing inside it and adding an alcohol-free fuel stabilizer and ethanol treatment before storage.

Those steps address different parts of the same storage problem. Filling the tank reduces the amount of humid air above the fuel. The treatment helps slow the oxidation that degrades gasoline while also helping manage the water problems associated with ethanol-blended fuel. Running the engine carries that treated fuel past the tank and into the fuel lines, carburetor, or injectors—the places where a small amount of deteriorated fuel can create starting problems months later.

The easiest order is to add the treatment first and then fill the tank. The incoming gasoline provides the mixing for you and makes it easier to get the treatment evenly distributed from the start. If the tank is already full, the treatment will still mix into the gasoline, especially once the engine runs, but adding it before the fill is the better practice.

Always check the owner's manual before putting a particular machine into long-term storage. Manufacturers differ on some details, especially on whether fuel should remain in a carburetor or the carburetor should be drained.

Why does gasoline go bad in equipment that sits?

Gasoline can start to deteriorate in as little as 30 days, according to Briggs & Stratton. The fuel gradually loses some of its most volatile components while oxidation reactions change the gasoline that remains. Ethanol-blended gasoline adds another storage concern because ethanol has a strong affinity for water, and most small-engine fuel systems are vented to the atmosphere.

Two problems can develop alongside each other inside a stored fuel system. As gasoline ages, oxidation can produce gums and other deposits that eventually interfere with small fuel passages. At the same time, ethanol-blended gasoline can accumulate water. If enough water enters the fuel for the blend to exceed its water tolerance, the ethanol-water mixture can separate from the gasoline and settle to the bottom of the tank. That condition is called phase separation.

That separated layer is especially troublesome because water and the ethanol-rich phase collect at low points in the fuel system, often near the fuel pickup or in a carburetor bowl. Water can promote corrosion, while deteriorated gasoline can leave deposits in carburetor jets and other passages measured in thousandths of an inch. That is why a machine that ran normally when it was parked can be difficult—or impossible—to start several months later.

Should you fill the tank or drain it before storage?

For equipment being stored with gasoline in it, fill the tank with fresh, properly treated fuel unless the manufacturer specifies a different storage procedure. Briggs & Stratton and Polaris both recommend full tanks of stabilized fuel for many of their gasoline-powered machines because reducing the empty space above the fuel helps limit condensation inside the tank.

That is why the advice to "fill it" and "drain it" can sound contradictory. They may be referring to different storage methods—or to different parts of the fuel system.

A full tank has less air space above the gasoline, which means less humid air available to exchange with the tank as temperatures change. A carburetor bowl presents a different problem. It holds a small amount of fuel in a vented part of the system, where evaporation can concentrate the heavier components of the gasoline and eventually leave deposits behind.

What to do with that carburetor depends on the equipment. Some manufacturers recommend circulating stabilized fuel through the carburetor and leaving it there. Others recommend treating the fuel first, running the engine long enough to distribute it, then shutting off the fuel supply and draining the carburetor or running the engine until it stalls. Follow the storage procedure in the owner's manual for that machine rather than applying one rule to every carbureted engine.

Fuel-injected machines do not have a carburetor bowl to drain. For those, the usual fuel-storage procedure is a full tank of fresh, stabilized gasoline followed by enough run time to move the treated fuel through the entire fuel system.

Bell Performance built Ethanol Defense for exactly this kind of storage problem. It combines fuel stabilizers with professional-strength, alcohol-free water-control chemistry designed to help ethanol-blended gasoline tolerate moisture and resist phase separation while it sits.

How long should you run the engine after adding stabilizer?

Run the engine long enough for treated fuel to replace untreated fuel everywhere downstream of the tank. Briggs & Stratton recommends running lawn equipment for a few minutes after adding stabilizer. Polaris specifies longer run times for some powersports equipment—typically 15 to 20 minutes for an ATV and 10 to 15 minutes for a snowmobile.

Follow the manufacturer's storage procedure when one is available. The goal is not simply to treat the gasoline sitting in the tank. The treated fuel needs time to travel through the fuel lines and into the carburetor or fuel-injection system. Otherwise, the tank may be protected while untreated gasoline remains elsewhere in the system for the next several months.

Do this outside or in a properly ventilated area. Once the machine is prepared for storage, leave it stored. Periodically starting an engine for a few minutes over the winter generally does more harm than good if the engine never reaches full operating temperature. Short runs can allow moisture to accumulate rather than giving the engine enough time to evaporate it. For battery maintenance, use an appropriate battery tender or maintainer rather than periodically starting the engine just to charge the battery.

What does each machine need before storage?

A mower, ATV, motorcycle, and snowmobile all face the same basic fuel problem during storage: gasoline that sits for months can oxidize, accumulate moisture, and leave deposits behind. The basic strategy is therefore similar—start with fresh fuel, treat it, and run the engine long enough to move the treated gasoline through the fuel system. What changes from one machine to the next is the manufacturer's recommended run time, the oil and battery maintenance, and what should be done with a carburetor if the machine has one.

Lawn mower, generator, and 4-cycle yard equipment

Add the treatment to fresh gasoline, top off the tank, and run the engine for a few minutes so treated fuel circulates through the system. If an oil change is due, changing the oil before storage removes the used oil and its accumulated contaminants rather than leaving them in the engine all winter. Clean grass and debris from mower decks, cooling fins, and other areas where it can trap moisture. Check the owner's manual for any additional storage steps specific to that engine.

ATV and UTV

Fill the tank with fresh fuel, add the treatment, and run the engine long enough to circulate the treated gasoline through the complete fuel system. Polaris specifies 15 to 20 minutes for some of its ATV storage procedures. Inflate the tires to the manufacturer's recommended pressure and maintain the battery with an appropriate battery tender or disconnect it according to the manufacturer's instructions.

Motorcycle

Add the treatment before the last ride of the season and fill the tank with fresh gasoline. That gives the treated fuel plenty of time to circulate through the entire fuel system before the motorcycle is parked. Change the engine oil and filter if called for by the manufacturer's storage or maintenance schedule, check the tires, and maintain the battery with an appropriate battery tender rather than periodically starting the motorcycle during storage.

Snowmobile (the off-season that lands in summer)

A snowmobile spends its off-season during some of the warmest and most humid months of the year, making fuel stability and moisture control especially important. Polaris recommends adding fuel treatment during the last rides of the season, completely filling the tank, and running the engine 10 to 15 minutes before storage.

Carbureted snowmobiles may require an additional step. Depending on the manufacturer's procedure, that can include shutting off the fuel supply and draining the carburetor or running the engine until the remaining fuel is consumed. Follow the owner's manual for the particular machine. If the manufacturer recommends fogging the engine for long-term storage, follow its procedure and use the specified fogging oil.

Do you still need a stabilizer if you use ethanol-free gas?

Yes. Ethanol-free gasoline removes one major storage concern—the water-related problems associated with ethanol—but it does not stop gasoline from aging. The fuel can still oxidize and lose volatile components while it sits, eventually contributing to gum, deposits, and poor starting. Ethanol-free gasoline is an excellent starting point for equipment that will sit for months, but treating it for long-term storage still makes sense.

Pay attention to the ethanol content at the pump as well. E15, gasoline containing up to 15% ethanol, is federally approved for use in model-year 2001 and newer cars and light-duty trucks. It is not approved for motorcycles, boats, snowmobiles, lawn mowers, and other off-road equipment. For the types of equipment covered in this guide, use ethanol-free gasoline or fuel containing no more ethanol than the equipment manufacturer allows.

If ethanol-free gasoline is available and approved for your equipment, fresh ethanol-free fuel plus a good stabilizing treatment gives you an excellent combination for off-season storage. If ethanol-free gasoline is not available, properly treated E10 can also be stored successfully. In either case, start with fresh fuel rather than trying to preserve gasoline that has already been sitting for months.

What are the treat rates for off-season storage?

Treat the tank on the way into storage

If a mower, ATV, motorcycle, snowmobile, or other gasoline-powered machine is about to sit for a season, take care of the fuel before you put it away. Starting with fresh gasoline, treating it before storage, and circulating that treated fuel through the system can prevent many of the fuel-related problems that show up when the machine comes back out months later.

Ethanol Defense stabilizes gasoline while adding professional-strength, alcohol-free water-control chemistry to help ethanol-blended fuel tolerate moisture and resist phase separation during storage. It treats up to 10 gallons per ounce, making it practical for everything from small lawn equipment to motorcycles, ATVs, UTVs, and snowmobiles.

See treat rates and find the right Bell Performance treatment for your equipment.