No, it is not recommended to use 15W-40 oil in a Harley Davidson motorcycle. Harley Davidson typically recommends using specific types of oil that meet their specifications, which are often 20W-50 weight oils.
Harley Davidson engines are air-cooled V-twin engines that operate at higher temperatures compared to liquid-cooled engines. The recommended viscosity, such as 20W-50, is carefully chosen to ensure proper lubrication and cooling of the engine components under these conditions.
Using a lower viscosity oil like 15W-40, which is commonly used in some automotive applications, may not provide sufficient lubrication and cooling properties for a Harley Davidson engine. It could potentially lead to increased friction, accelerated wear, and reduced engine performance.
To ensure the best performance and longevity of your Harley Davidson motorcycle, it's always advisable to use the oil recommended by the manufacturer and follow their guidelines for oil changes and maintenance.