A gasoline engine oil is formulated differently to a HDD (heavy duty diesel) oil, the main reason for this is the need to handle the combustion by products that are created (diesel is dirtier than gasoline). If you were to use a gasoline oil in a heavy duty truck you could expect to see high levels of sludge, wear and eventual engine problems; however using the other way around can have advantages. Sludge protection and deposit control on HD lubricants are strong as well as wear protection. On most high performance engine lubricants you will see that they have both diesel (API C) and gasoline (API S) performance.