While the recommended engine oil grade for the Royal Enfield Classic 350 is 15W50, using Castrol Magnatec 10W40 oil as an alternative can be considered, but it may not provide the optimal performance and protection specifically designed for the Classic 350's engine.
Here are a few important points to consider:
Viscosity: The numbers "10W40" represent the oil's viscosity rating. The first number, 10W, indicates the oil's viscosity at cold temperatures, while the second number, 40, indicates the viscosity at operating temperatures. The recommended 15W50 oil has a higher viscosity rating, indicating that it provides better protection and lubrication at higher operating temperatures, which is beneficial for Royal Enfield engines known for their air-cooled design and higher heat generation. Using a lower viscosity oil like 10W40 may result in reduced protection under extreme heat conditions.
Manufacturer Recommendations: It is generally advisable to follow the manufacturer's recommendations regarding oil grade and viscosity to ensure optimal performance and engine longevity. Royal Enfield recommends 15W50 oil for the Classic 350 for a reason, as it is specifically chosen to match the engine's requirements.
Riding Conditions: Consider the prevailing riding conditions and climate in your area. If you frequently ride in hot or extreme temperature conditions, using a higher viscosity oil like 15W50 can provide better protection against heat-related engine wear.
While using Castrol Magnatec 10W40 oil might not cause immediate harm, it's essential to understand that the recommended oil grade is selected to provide the best performance and protection for your Royal Enfield Classic 350. It is recommended to consult with a Royal Enfield authorized service center or refer to the owner's manual for the most accurate and specific guidance regarding the appropriate engine oil for your motorcycle model.