Many years ago I ran single weight oils that unlike multiweight oils today had to be changed depending on outside temperatures the motor was operated in. In eastern Kentucky in winter I would run a 20 weight oil and in summer a heavier 30 weight oil. The first summer I headed west to the desert I was shocked to see my oil light flicker at idle and went to 40 weight oil. It is amazing with the technology we have to still have manufacturers being allowed to sell low quality products that can harm motors.