Using 5W-30 instead of 10W-30 in your Honda CRF 300L street and trail dirt bike might not be ideal. The oil viscosity rating, such as 5W-30 or 10W-30, indicates the oil's flow characteristics at different temperatures.
The "W" stands for winter, and the number preceding it represents the oil's viscosity at low temperatures, while the number after the "W" represents the oil's viscosity at higher temperatures. In this case, 5W-30 is thinner at low temperatures than 10W-30.
The manufacturer typically recommends a specific oil viscosity to ensure optimal performance and protection for the engine. It's best to refer to your bike's owner's manual or contact a Honda dealer to determine the recommended oil viscosity for your specific model.
Using a different viscosity oil than recommended may affect the engine's lubrication and performance, especially if the oil is too thin or thick for the operating conditions. It's always best to follow the manufacturer's guidelines to ensure the longevity and reliability of your motorcycle's engine.