The use of oil in a motorcycle engine is essential for its proper functioning and longevity. When selecting an oil for your Yamaha FZ 25, it's important to refer to the manufacturer's recommendations to ensure compatibility and optimal performance.
According to Yamaha's official recommendations, the recommended engine oil viscosity for the Yamaha FZ 25 is 20W40. This means that the oil should have a viscosity rating of 20 in cold temperatures and 40 in hot temperatures.
The 10W50 Motul oil you mentioned has a different viscosity rating, with a lower number for cold temperatures and a higher number for hot temperatures. While it might be within the acceptable viscosity range for some motorcycles, it is not the recommended specification for the Yamaha FZ 25.
To maintain the best performance and reliability of your motorcycle, it is advisable to use the recommended oil viscosity, which is 20W40 in this case. It is always a good idea to follow the manufacturer's guidelines to ensure proper lubrication and avoid any potential issues that might arise from using an incompatible oil.