FCP has a good oil article up

[matthew1]

Not to start an oil flame war, but this is in-depth. It goes from basics to advanced, and is well-written. I can't comment on the accuracy because I haven't studied oil at length.

What is the best oil for my car?

Basics

Operation from the engine itself is also dirty. Internal combustion creates microscopic coke particles and black soot, which is accumulated by your vehicles motor oil. This is why motor oil always drains black and smells burnt. It is also why it is important to perform routine oil changes. Motor oil helps clean the inside of the engine with its additive package, as well. These additives can help fight deposits, rust, and corrosion.

Surprise (to me)

Motor oil performs another necessary aspect for your engine; it keeps it cool.

[jblackburn]

Re: that last one. Remember "oil cooling jets" for the bottom of pistons? Major example of that there. Many high-powered transmissions have oil jets at the gears too.

Oil helps cool the bearings and lower end; water and oil helps cool the top.

A heavier weight oil handles heat better by maintaining its viscosity properties, but should still be selected according to manufacturer recommendations.