there is such a thing as too thick. What happened with 20/50? Amsoil makes a 20/50 fyi.So I found out my mechanic put in 5w30. I started toying with viscosity. Went to Rotella 10w40, light still came on at hot idle. Went to Mobile 1 15w50, better yet but light still came on after a while. During oil changes noticed oil cooler lines leaking. Not sure if it contributed to problem, but replaced lines and put Liqui Moly 10w60, and haven't had a problem since, even at 100 degree temps outside. I finally have an everyday driver.