Well, I asked this question because I had an appt for the 7,500 mile service today (free),which has to be done before 9,000 for it to be free, and I was getting close to the limit. I thought I had 2 gallons of S2k, but one of the gallons was the 15W40, so I was in a bind. I had them put in 4 qts of S2K 0W30, and 2 qts of 15W40, and they filled the Blackstone bottle with the used. Anyone have any idea what vis. oil I now have in my crank? Have I made a huge mistake? Depending on the UOA results, I will go with either a less expensive Amsoil (5W30?), or RedLine (5W30 or 5W40). Redline gets the nod if the S2K was beaten up, and Amsoil gets the nod if the Amsoil was in good shape.