How Ethanol in Gasoline Damages Small Engines

If there's one thing we wish every lawn mower owner understood, it's the damage that ethanol-blended gasoline does to small engines. Most gas sold in the US contains 10% ethanol (E10), and it's responsible for a huge percentage of the repair work we see.

Ethanol attracts water. This process, called phase separation, happens when ethanol absorbs moisture from the air. Over time, the ethanol and water separate from the gasoline and settle to the bottom of the tank. This water-ethanol mixture gets sucked into the carburetor and engine, where it causes corrosion, hard starting, and poor performance.

Ethanol dissolves rubber and plastic. Many older small engines have fuel lines, gaskets, and carburetor components made from materials that weren't designed to handle ethanol. The ethanol breaks these parts down, creating leaks and introducing debris into the fuel system.

Ethanol goes bad faster. Regular gasoline has a shelf life of about 3-6 months. Ethanol-blended fuel can start degrading in as little as 30 days, especially in the small, vented fuel tanks common on outdoor power equipment.

Ethanol leaves deposits. As ethanol-blended fuel deteriorates, it leaves behind a sticky, varnish-like residue that clogs carburetor jets, fuel filters, and fuel lines. This is the number one cause of the 'my mower won't start in spring' calls we get every year.

What can you do about it? First, use ethanol-free gas whenever possible. Many gas stations sell ethanol-free premium — look for signs that say 'No Ethanol' or 'Rec-90.' You can find ethanol-free stations at pure-gas.org. Second, always use fuel stabilizer when storing equipment. Products like Sta-Bil or Sea Foam help prevent the worst effects of ethanol. Third, never let fuel sit in your equipment for more than 30 days without stabilizer.

If your mower has been sitting with old ethanol fuel and won't start, bring it to us. A carburetor cleaning and fresh fuel usually gets it running again.