Generally potassium indicates anti-freeze in the oil, since the water boils off, and the glycol may not show much either. It can be from other things though. Rotella ain't all that great, try Mobil or Amsoil synthetics if you can afford it, if not then use Delvac-1300 or Delo-400, which are a much better product than the Shell. Do a search on this forum, oils have been discussed ad nauseum here!
