Gasoline at the pump often contains up to 10% ethanol (E10). That works fine for daily driving, but small engines and seasonal equipment can sit for months, and stored fuel ages. The steps below are general good practice. Follow your equipment manual for the fuels it allows, and your local fire code for how much fuel you may store and where.
How ethanol affects stored fuel
Ethanol attracts moisture. If enough water gets into the fuel, the ethanol and water can separate from the gasoline and settle to the bottom of the tank or can. This is called phase separation. An engine that draws from that bottom layer may run poorly or not at all. Gasoline also oxidizes as it ages, which can leave varnish and gum in the small passages of a carburetor.
Fuel storage checklist
- Use approved containers made for gasoline, with tight caps. Keep vents closed in storage.
- Fill containers on the ground, not in a truck bed or trunk.
- Buy only what you’ll use in a reasonable time, and use the oldest fuel first.
- Label every can with the date, and with the ratio if it’s 2-stroke mix.
- Leave room for expansion. Don’t fill containers to the brim.
- Store it cool, dry and ventilated, out of direct sun, away from living spaces and ignition sources like furnaces, water heaters and pilot lights, and out of children’s reach.
- Keep containers sealed to limit moisture and evaporation.
- Use the fuel your manual allows. Many small engines specify no more than E10. Check the manual and the pump label.
- Add stabilizer while the fuel is fresh, if you use one, at the dose on the label.
What to do with old fuel
Fuel that looks cloudy or dark, shows separate layers or water, or smells sour shouldn’t go into a small engine. Never pour it on the ground or down a drain. Many local household hazardous waste programs accept old gasoline. For storage steps for specific equipment, see the generator, lawn mower and chainsaw guides.
Frequently asked questions
How long can I store gasoline?
It depends on the fuel, the container and the storage conditions. Untreated gasoline doesn’t keep indefinitely. Follow your equipment manual, and if you use a fuel stabilizer, the storage time on its label.
What is phase separation?
When ethanol-blended gasoline absorbs enough water, the ethanol and water can separate from the gasoline and sink to the bottom of the tank. Fuel that has phase-separated generally shouldn’t be used and should be disposed of properly.
Can I use E15 in my mower or chainsaw?
Check the owner’s manual and the label on the fuel pump. Many small engines specify E10 or less.
AMSOIL fuel treatments for stored gasoline
- AMSOIL Gasoline Stabilizer. AMSOIL says it “helps keep fuel fresh up to 12 months,” “protects against varnish and gum buildup” and is “effective in ethanol-blended fuel.”
- AMSOIL Quickshot Gasoline Treatment and Stabilizer. AMSOIL says it “helps prevent water-induced ethanol separation and breakdown” and is “designed to keep water due to ethanol dispersed in tiny molecules throughout the fuel tank, moving it out as a normal part of operation.”
Product wording above is quoted or summarized from amsoil.com. Read each product’s label and data sheet for directions.
To see which AMSOIL products are listed for your equipment, use AMSOIL’s official lookup guide.