Based on all the reading I did on the subject before I made the switch to Mobil 1 synthetic about 7 years ago you should break a new or rebuilt engine in using conventional motor oil and then switch to synthetic after break in.
I am running synthetic in my 350 cu in. Gen 1 non roller cam Chevy V-8's, I have 3, and in my 1985 5.0 HO roller cam Ford.
No problems to report.
Last edited by Hot Rod John; 12/05/2010 2:51 PM.
