Why Are There So Many Different Engine Oils?

Because there are countless engines, different in purpose, and countless manufacturers making them. And each manufacturer has its own production technologies.

For example, if one engine is designed to be powerful, for sports cars, another is conceived by its designers from the start for economical city runabouts. A third group of engines is intended more for towing trailers and driving over hilly terrain.

There are actually a great many ways engines get positioned in the market. And the carmaker, right from the start, builds specific expected operating conditions for each engine into the design brief given to its engineers. The engineers' job is then to optimise the engine's design as much as possible for exactly those given conditions.

Hence the huge variety of engines, differing in displacement, design, and, importantly, in the materials used to make their internal parts. All these factors, in turn, call for stricter requirements on the engine oil that will be used with them. And some engine-oil parameters are actually mutually exclusive across different engines.

For instance, everyone knows that as engine speed rises, oil temperature rises too. And accordingly, as oil temperature rises, its viscosity drops. But did you know that the working rev range differs from one engine to another? That is, if, say, at the same gear and an engine speed of, say, 3,000 rpm, one car is doing 110 km/h, another car under the same conditions might be doing 140, and a third one 160.

It's obvious that these three cars need oils with completely different parameters for their engines to run properly.