The Role of Oil
Oil enjoys four critical roles in internal combustion engines. Motor oil Lubricates, Protects, Cleans and Cools the engine. Let’s examine these roles more closely.

Lubricates
Motor oil must lubricate engine components so that they will easily pass by one another without a significant loss of power due to friction. At start-up, this is especially true.  As an engine sits, oil tends to run down into the oil sump. Therefore, when the engine is started, the oil must be quickly pumped throughout the engine to provide sufficient cranking speed for the engine to turn over.  Once the engine is running, engine oil must create a film between moving parts to make them “slippery” which increases power, performance and efficiency.  Each different type of engine requires a certain viscosity range in order that the oil will provide an adequate film between moving parts while still flowing quickly and easily enough throughout the engine.

Protects
While engine oil provides a lubricating film between metal surfaces, it does more than just lubricate. It helps to prevent engine parts from coming into contact with each other … motor oils protect against wear.  An engine oil must also protect against the corrosion of engine parts. Oil oxidation can be accelerated by high oil temperatures and copper. The oxidation of motor oil as well as contaminates created by condensation and combustion by-products can also create harmful acids. Oxidation thickens oil, creates acids, and degrades viscosity, all of which reduces engine life.. Oxidized oil can cause deposits on engine pistons and valves, stuck rings, bore polishing, scuffing and sticking.  Engine oils (specifically, their additive packages) are designed to combat these harmful effects.

Cleans
Dirty engines aren’t efficient. Deposits within an engine gum up internal workings and reduce fuel efficiency while decreasing engine of performance and fuel efficiency.  Additionally, oil contaminants left unchecked can result in incalculable wear within an engine.  While filtration is designed to remedy much of this problem, oil continues to play an essential roll by discouraging deposits from forming and by maintaining contaminants in suspension until they can be removed by the oil filter.

Cools
Engine oil is responsible for much off the cooling that takes place within an engine. The radiator only cools the upper portion of the engine.
The balance (crankshaft, camshaft, timing gears, pistons, main and connecting rod bearings and numerous other critical engine components) are cooled primarily by oil circulating within your engine.  Engine heat is generated from both the combustion process as well as the friction created by moving parts. As oil passes through the system it is directed onto these hot surfaces in order to carry the heat away to the oil sump.

Additive Package
Clearly, an engine oil performs a number of critical functions. Again, they include lubrication, cooling, cleaning and suspending, and protecting metal surfaces against wear and corrosion damage. A Lubricant comprises a base fluid (mineral oil, synthetic oil) and an additive package.  While the primary function of the base fluid is to lubricate, it also acts as a vehicle for the additives. Additives serve both to enhance the already existing properties of the base fluid, and to provide additional new properties. Already existing properties include viscosity, viscosity index, pour point, and oxidation resistance. Those new properties introduced by additives include cleaning and suspending ability, anti-wear performance, and corrosion control.
Over the decades, oil additives which solved a variety of engine problems were developed. They helped to protect against corrosion, to keep particles such as soot dispersed, the ability to prohibit acidic combustion products from plating out as varnish on engine surfaces, and the ability to minimize wear by providing a chemical film on heavily loaded surfaces.
In addition, engine oils became further specialized in order to satisfy the requirements of diesel engine oils, which began to diverge from requirements for gasoline combustion engines, since enhanced dispersive capability was needed to keep soot from clumping in the oil of diesel engines.
Simply put, motor oil is the essential element in maintaining fuel efficiency, engine health and longevity and reduced downtime. Protecting, Enhancing and Prolonging its useful life is paramount.