Is 87 Octane Gas Suitable for Lawn Mowers?

Lawn mowers are designed to handle various fuel types, but the question often arises whether 87 octane gas with 10% ethanol (E10) is suitable. This article explores the suitability of 87 octane gas for lawn mowers, addressing common concerns and providing expert guidance.

Understanding Octane Ratings and Ethanol Content

The octane rating of fuel, which measures the resistance of a fuel to igniting prematurely, is a critical factor in determining its suitability for lawn mowers. Many lawn mowers specify a maximum ethanol content and a minimum octane rating. Generally, 87 octane is the recommended minimum octane rating for lawn mowers, with some models capable of using higher octane fuels, like E15, if available and appropriate.

Common Fuel Recommendations for Lawn Mowers

Lawn mowers today typically require a fuel with a maximum ethanol content of 10% (E10). Some newer models allow up to 15% ethanol (E15), often referred to as UNL88, which has an effective octane rating of 88. Using higher octane fuels beyond this range, such as 89 or 91 octane, can be done but is largely unnecessary and may only result in waste.

The general consensus is that using fuel with an octane rating at or below the maximum allowable ethanol content (E10 or E15) is advised, but not strictly required for most lawn mowers under normal operating conditions. This advice is particularly applicable for outdoor temperatures above 95°F (35°C). However, octane ratings higher than 89 may be considered overkill, as the benefits are negligible.

Effects of Octane and Ethanol on Engine Performance

Fuel with higher octane ratings may contain additives that slightly decrease the energy density of the fuel, potentially making the engine run slightly lean (with more air for the amount of fuel). This change is usually minimal and may be offset by the solvent properties of ethanol. Ethanol is more effective at cleaning engine components, but it also deteriorates more quickly, especially if left in the fuel system for extended periods.

For optimal performance, many modern engines are tuned to run efficiently on E10 fuel with an 87 octane rating. They may run fine on 86 or even 85 octane, but only if the ambient temperatures are not too high. It is generally not recommended to attempt using lower octane ratings, as this could result in the engine running slightly on the rich side, with too much fuel for the amount of air. This richer mixture may cause the engine to run cooler and produce more power in an air-cooled engine, potentially leading to less wear.

Considering Ethanol for Long-Term Storage and Use

Ethanol is a very effective solvent that helps prevent gum and varnish buildup in engine components, especially in small carbureted engines like those found in lawn mowers. However, the quality of ethanol and its freshness are crucial. E10 fuel should be used within 30 days of purchase, and during winter storage, non-ethanol or stabilized E10 is preferred.

For storage over winter, or if the fuel is expected to sit for more than 30 days, it is recommended to use either non-ethanol fuel or add fuel stabilizer to E10 fuel. Fuel stabilizers can extend the stability of the fuel but should not be left in the carburetor for more than a month. Non-ethanol fuel, on the other hand, can last about a year in the carburetor without significant issues.

Practical Recommendations for Lawn Mower Fuel Selection

Based on experience and practical considerations, the following methods are recommended for maintaining lawn mower engines:

Non-Ethanol All the Time: Use exclusively non-ethanol fuel and store any leftover stabilized E10 in a separate container. Stabilized Ethanol E10 All the Time: Use stabilized E10 for all fuel needs, which can be the most convenient and cost-effective option. Rotational System: Refill the mower tank and storage can with stabilized E10 throughout the season, ensuring the carburetor is completely dry or run to full temperature at least once a month. Wintertime Preparation: Drain the carburetor of fuel and run the engine to full temperature at least once a month during winter. Ensure the storage can is filled with non-ethanol fuel or stabilized E10, and run the carburetor dry before storage.

Regardless of the method chosen, it is important to follow a consistent maintenance routine to ensure optimal performance and longevity of the lawn mower engine.

Conclusion

In conclusion, using 87 octane gas with 10% ethanol (E10) is generally suitable for lawn mowers, and higher octane ratings may only be necessary in extreme situations. Regular use of stabilized E10 or non-ethanol fuel can help maintain engine cleanliness and efficiency. Proper storage and regular maintenance are crucial for extending the life of lawn mower engines, and a balanced approach to fuel selection can help achieve the best results.