I've not come in in awhile, and looks like people have already forgotten - Castrol buys its oil from ShellBoth are not true synthetic, but are highly processed mineral oil that just meets the spec that allows them to call it synthetic oil in some countries, although there are countries e.g. in the EU that prohibit them from calling it synthetic.
Synthetic oil is just base stock. What is really important is the additive package that is inside the oil.
Its not the oil that cleans or protect the engine, its the additives. I know calcium is an important detergent.
W/o good additives, having a fantastic base stock does nothing. Even POE also useless.
Both are not true synthetic, but are highly processed mineral oil that just meets the spec that allows them to call it synthetic oil in some countries, although there are countries e.g. in the EU that prohibit them from calling it synthetic.
