It is generally recommended to use the oil viscosity specified by the manufacturer for your Honda lawn mower. While 5W-30 and 10W-30 are both multi-grade oils, they have different viscosity characteristics that can affect engine performance and lubrication.
Using 5W-30 oil instead of 10W-30 in your Honda lawn mower may not provide the optimal lubrication and protection for the engine, especially in certain temperature conditions. The numbers in the oil viscosity rating represent its flow characteristics at different temperatures. The "W" stands for winter, and the lower the number, the better the oil flows at colder temperatures.
If your Honda lawn mower manufacturer recommends 10W-30 oil, it means they have determined that it provides the ideal viscosity range for the mower's engine across a broad range of operating temperatures. 10W-30 oil provides adequate lubrication at higher temperatures while maintaining sufficient flow at lower temperatures during startup.
Using 5W-30 oil in a lawn mower designed for 10W-30 may result in reduced lubrication at higher temperatures, potentially leading to increased engine wear and decreased performance.
To ensure the best performance and longevity of your Honda lawn mower, it is recommended to follow the manufacturer's guidelines and use the specified oil viscosity, which in this case would be 10W-30. Refer to the owner's manual or consult with a Honda authorized dealer or service center for specific recommendations based on your lawn mower model.