This is a really good article by AMSOIL on 5 myths of motor oil that are not true!

1. 1. When motor oil turn black it must be changed
   2. You must change oil every 3000 miles
   3. You can’t mix synthetic and conventional motor oil
   4. Once you switch to synthetic you can’t go back
   5. Synthetic oil causes engines to leak oil

Also there is a good video with Gale Banks on “what’s in synthetic motor oil’!