I used to have a Ford Diesel that I used T-6 5w-40 full synthetic oil in it. This oil was designed to be used in Diesel engines. I know that it can be used in some gas engines I was wondering since I have that oil would it be OK to use just one time in my truck with a 4.6 engine in it? I dont think that it would hurt, but I want somebody with more knowledge about this then I have to give me their opinion.