Quote Originally Posted by tom p. View Post
The domestic mfrs are just starting to follow the lead of the Euro mfrs. who have had highly-specific, published oil specs for decades.
Huh? GM has had specs for everything, forever, from TPC`s (Tire Performance Criteria), to um, Dexron transmission fluid, to specs for oil. Quoting from a 2004 owner`s manual I just happen to have sitting here:

"Your vehicle`s engine requires a special oil meeting GM Standard GM4718M. Oils meeting this standard may be identified as synthetic. However not all synthetic oils will meet this GM standard. You should look for and use only an oil that meets GM Standard GM4718M."