It is the degree of viscosity that is used to classify oil for 4-stroke engine lubricants for working in cold weather and hot, according to the SAE (Society of Automotive Engineers). 5W (W = winter) is the degree of viscosity in cold or winter. While this number smaller, more fluid is oil in frio.40 is the degree of viscosity in hot or summer. While the bigger this number, more viscous oil is hot.
