BASE OIL
There are two main components that any motor oil is made of. There is a base fluid (sometimes called a basestock) and the additive package. The base fluid typically makes up the bulk of the oil. Additive chemicals are then added to enhance the positive qualities of the basestock and to overcome whatever negative qualities there may be.

WHAT ARE THE REQUIREMENTS OF ENGINE OIL?
Motor oil must create a film between moving parts to make them "slippery" which increases power, performance and efficiency. The film that a motor oil provides between metal surfaces does more than just lubricate though. By keeping engine components from coming in contact with each other, a motor oil also provides protection against wear.
Motor oil must also protect against corrosion of engine components. Oxidation of the oil and contamination from condensation and combustion by-products which cause acids within an engine oil. Additives in engine oils are designed to combat these acids.

Motor oil is responsible for a large percentage of the cooling that takes place within the lower part of your engine. Your radiator (cooling system) is only responsible for cooling the upper portion of your engine. The rest (crankshaft, camshaft, timing gears, main and connecting rod bearings and many other critical engine components are cooled mainly by the motor oil within your engine. Heat is generated within an engine from both the combustion process and the friction caused by the motion of engine components. As oil passes through the system it is directed onto these hot surfaces in order to carry much of the heat away.
That is why running even a litre low on oil can elevate lower engine temperatures. As this is not part of the liquid cooling system, your temperature gauge won't show lower engine temperatures until it is too late.