When it comes to fueling your lawn mower for optimal performance and longevity, several factors come into play, including the type of mower, the recommended fuel by the manufacturer, and the quality and grade of gasoline used. Most push lawn mowers with four-stroke engines are designed to run on regular unleaded gasoline with an octane rating of 87. Using a higher octane fuel, like premium, typically doesn’t improve performance or fuel efficiency in these engines; it mainly benefits high-compression or turbocharged engines, which are uncommon in lawn mowers. Therefore, unless your mower’s manual explicitly states otherwise, regular 87 octane gas is both sufficient and cost-effective.

For two-stroke engines, which are common in string trimmers and some smaller mowers, a mix of gasoline and two-cycle oil is necessary. Always follow the manufacturer’s specified ratio to prevent engine damage or loss of power.

The choice of fuel blends is another consideration. Many modern gasoline options include ethanol (commonly E10, which is 10% ethanol). While small amounts of ethanol generally don’t harm most lawn mower engines, ethanol is a solvent that can attract moisture and lead to phase separation, causing engine issues, especially if gas sits unused for long periods. Therefore, if your mower will be unused for a season or more, it’s advisable to use an ethanol-free gasoline or add a fuel stabilizer to prevent degradation.

Speaking of fuel stability, gas older than 30 days can start to degrade, leading to varnish buildup, clogged carburetors, and poor engine performance. To maintain your mower’s health, you should replenish the fuel supply before storage and consider emptying the tank if the mower won’t be used for several months. Adding a fuel stabilizer helps prolong the gas’s life up to six months or more.

Avoid using gasoline with more than 10% ethanol, as higher blends like E15 or E85 are not recommended for small engines and can cause damage. Similarly, avoid mixing diesel or other fuels not intended for your mower.

In summary, the best practice is:

• Use regular unleaded 87 octane gas unless your mower manual specifies otherwise.
• For two-stroke engines, mix fuel and oil at the recommended ratio.
• Prefer ethanol-free gasoline if available, or use fuel stabilizers to protect fuel quality.
• Avoid gasoline older than 30 days without stabilization.
• Never use fuels with ethanol content higher than recommended.
• Replace fuel regularly and empty tanks before long-term storage.

By following these guidelines, you ensure your lawn mower runs smoothly, efficiently, and enjoys a longer lifespan. Consistently using the proper fuel maintains engine health, avoids costly repairs, and keeps your mower ready whenever you need it.