I have run Spectral synthetic blend 10/40 for many years. Last winter I won a gallon of 10/40 Bellray Dino oil. Mid summer I was due for an oil change so I used the Bellray. Before I logged 5,000 miles I was noticing a different sound to the motor. At just shy of the 5,000 mile mark I changed oil and went back to the Spectral blend. At the first start up the motor ran quieter and clutch engagement was smoother.