Hmm the old what weight oil I should use.
I live in Australia and Just got a new SS Commodore which is a Pontiac in the US or something. It has a L77 6L V8.
Just finished with a nice " Drive It like you stole it Break In" (of course only when the engine is warn). Its done about 1024km when I dropped the oil for 2nd time (fist time I did it at 200km).
New oil that I put in is Penrite 5W-60 Full Synthetic (Grp 4 & 5). Holden here spec this engine for a 5w30 which is the norm but it varies from dealer to dealer. I will tell you one thing, don't believe what the dealer tells you. They are using light weight oils to meet the CAFE requirements and emission levels.
Clearances on engines cant go any tighter than what they are. If they do excessive metal to metal contact will occur no matter what oil you use. Tolerances on the other hand do improve with new machining techniques and development. If mass manufactures decreased their clearances, boy would a lot of engines just go bang. When building a tight engine every part is measured 2-3 times to ensure all clearances as with spec. I cant see GM or Ford doing this on the production line.
Anyways I have clocked up about 250km with the new oil. The engine runs smoother, quieter.
In regards to people saying that you will not have enough flow with thicker oil they seem to forget that flow and pressure are related.
Go the thick stuff
Its a V8 not a 2L milk bottle.