Originally Posted by AmericanSensei
I find it a waste of money personally, But it really depends on who you ask. The difference is so little it's not worth it. Oil is not what it was years and years ago. Well known, name brand oil typically already comes with additives in it. I have never nor will I ever use Additives in my fuel or oil, I just buy good oil.
Synthetic oil is good. A lot of dragsters actually run diesel oil. 15w 50 or 15w40 diesel oil. It used to have zinc in it, which actually puts a protective coating over everything. But the new, "lower emissions" stuff doesnt have any of the zinc in it anymore.
But synthetic oil is good for engines, but if you put synthetic oil in an engine that already has 100k miles on it, and has been running normal oil, it can be bad. An older engine might have gunk and stuff that keeps the gaskets plugged up so that when you run synthetic, and everything gets cleared out, leaks develop.
If you want to clean your engine out though, put sea foam in your oil, run it for about 500 miles before changing it, and make sure you get a few redline shifts in there.