I switched to Amsoil about 5 months and 4,000 miles ago. My mechanic says that I don't need to change it again until 10k or a year; but after reading a bunch of posts about synthetic oil I was wondering if anyone else waits that long. I've read some posts of people who say that 10k is way to long to wait to change it, even on Amsoil. Has anyone had any problems waiting the recommended time to change their oil, or is everyone just going by the rule that it is good to change it every 3k-5k miles?