@Dear all
Engine oil has two basic characteristics 1st it's Viscosity which is shown by SAE Viscosity Grade
and second is its performance grade which is shown by API Grading
So SAE Grading only shows their thickness or thinness where as the API Grading shows their performance level so where as the oils of same viscosity grades are concerns like SAE 20W-50 it only shows that their Viscosity is same but second grading of API which shows which oil is best in performance (like performance in high temperature, perfromaance in low temperature , cold starting, evaporation loss, flash point , pour point , sulphated ash ect.. ) so in this regard latest API Graded oil is always the best choice to use in one's car
Thanks