You won't believe this one. My dealer said that Syn oil is bad for the seals. He also said if I wanted to do my own oil changes, I had to get receipts to prove it, in order not to void warranty. I laughed. You shouldn't use it before roughly 5000 miles, due to proper break-in time, but after that, it's the best thing you can do. Oh yeah, if anyone was wondering about oil filters, Mobil 1 filters are the best, and yes, they are better than K&N.