Srt8 charger. We got rotella 5w-40 for it, the rotella bottle says it meets sm automotive so I think this is a good choice. However, the RT use 5w-20 and the v6 5w-30. Why? Is the 5w-40 just for show? LIke so that mobil can endorse it? There aren't too many 5w-40 oils and there is only 1 OW-40, mobil's, that I am aware of. When the warranty is up, can we go to a 10w-30 synthetic or 5w-30 synthetic or will this hurt our motor ? Thanx. Just seems wierd that the srt8 needs the 40 weight but the rt needs a 20.