I don't know about Valvoline, but I wouldn't use Castrol.
Their oil is dyno based, but they remove up to like %70 percent of some component from the oil and then add a synthetic additive. Mobil one and others tried to sue them because they (Castrol) was claiming a fully synthetic oil when it wasn't. Eventually they lost because they found that even though their oil is dyno based, removing that part of the conventional oil (for the love of god I can't remember what it was) and adding in that additive defines it as not a "natural" oil and thereby by default making it a "synthetic" oil. That other %30 percent of the formula is what contains the high amounts of ash which isn't good.
Originally posted by 99REDSE:
i use valvoline syntec, is that bad? 
