Kaiser, I have been using the generic STP from wal-mart for the other two vehicles but since I bought the XF, they have not carried it anymore. When I changed the oil last august in my XF, I used STP engine oil treatment. Before I used it, I asked STP if it was certified for use in an engine that required synthetic oil. STP replied it is certified safe and compatable with all oils including blends and full synthetic. Since the XF uses almost twice the oil of new vehicles today, I use two 15oz bottles. By far the cheapest enging protection. In my opinion, all the rest are just more expensive versions of Ole reliable. In this case, cheaper IS both better, and cost effective. Again, until engine manufacturers provide for oil flow before cranking, use STP. Don't forget to follow their mixing instructions for the volume of oil used! IMHO, the concerns with the FSS and 'feelie good' concerns with 'othe'r brands of products, do not justify paying those prices.