15w40 oils such as Rotella, Chevron delo and mobil delvac I thought were for diesel engines, not gas. I was told that the additives in oils designed for diesel engines can form deposits around the pistons in a gas engine so they shouldn't be used in a gas motor. Is that true? I read so much about people using rotella and delo and delvac in gas engines, isn't that bad or am I missing something? What about using 15w40 (diesel) oils in 4-cyl and V-8 marine gas engines?