Engine Design and Engine Oil

This whole philosophy directly affects manufacturing, including how engines are built. Manufacturers use different technologies, and to no small degree those are dictated by how the car brand positions itself. Accordingly, the materials used to make the internal engine parts differ too. And that's exactly where the chemistry begins — the question of how the additives in an engine oil interact with those very materials used in building the engine.

Since every oil manufacturer uses different additives, it turns out that one and the same oil can be perfectly suited to one engine, and literally within a couple of years destroy (say, by eating away at the piston rings) another, similar engine from a different manufacturer. There's no such thing as "this engine oil is better, and that one is worse," engine oils are simply all DIFFERENT, designed for different engines and operating conditions.

There's also the critical matter of the film thickness the oil forms on a car's internal parts (some additives regulate exactly that). If this thickness exceeds the clearances allowed by the engine manufacturer, the piston assembly will keep overheating, with all the consequences that follow; if it's too thin, the oil will simply burn off faster than it should. And the allowable clearances happen to differ across every car maker — in fact, they even differ between different engines from the same maker.