I bought the mobil 1 oil on sale and a good filter and brought the car to valvoline instant oil change to let them do the work. They charged me like a regular oil change even though I brought the oil and filter. That was no problem for me, I felt it was worth it, however when I asked the technician if I could use the valvoline snythetic oil in the future , He told me no, it would be a bad idea. He says that once you start with the mobil 1 you have to continue using it or the seals or valves will get screwed up in the car. I don't know a whole lot about engines, Is this true.