Oils and Lubes

Detergents

The purpose is to keep the surfaces of your engine parts clean by inhibiting the formation of high-temperature deposits, rust and corrosion.

Dispersants

These additives disperse solid particles, keeping them in solution, so they don't come together to form sludge, varnish and acids. Some additives work both as detergents and dispersants.

Antiwear Agents

There are times when the lubricating film breaks down, so the antiwear agents have to protect the metal surfaces. A zinc and phosphorus compound called ZDDP along with other phosphorus (and sulphur) compounds are commonly used.

Friction Modifiers

These reduce engine friction and therefore can improve fuel economy. Graphite, molybdenum and other compounds are used.

Pour-Point Depressants

Oil contains wax particles that can congeal and reduce flow, so these additives are used to prevent that occurring.

Antioxidants

This prevents oxidation (thickening) of oil. Some of the additives that perform other functions also serve this purpose, such as the antiwear agents.

Foam Inhibitors

The crankshaft whipping through the oil in the pan causes foaming. Oil foam is not as effective a lubricant as a full-liquid stream, so the inhibitors are used to cause the foam bubbles to collapse.

Rust/Corrosion Inhibitors

Used to protect metal parts from acids and moisture.

Viscosity

Viscosity is a measure of the oil's thickness/resistance to flow. There are 2 numbers in the viscosity rating - eg. 30W-50. The first number relates to viscosity at cold temperatures, and the higher the 2nd number, the more resistant it is to thinning. Within reason, thicker oil generally seals better and maintains a better film of lubrication between moving parts.

Generally, if viscosity is too low, oil can sheer and loose film strength at high temps. If too high, oil may not pump to the proper parts of the engine when temps are low and the film may tear at high rpm. So 10W-30 oil has less viscosity when cold and hot than does 20W-50. What's really important is that you use the oil viscosity your car's owner's manual recommends.

Multiviscousity

Multiviscous oils are one of the great improvements in oils but choose wisely - these oils are more prone to viscosity and thermal breakdown due to the high polymer content. For an engine used fairly little, when oil changes are infrequent, multi-viscosity oils are important so that lubrication is adequate in either winter or summer. The rule of thumb when selecting a multiviscous oil to select one with the narrowest span of viscosity for the temperature you will use it in.

Viscosity Index

Resistance to thinning with increasing temperature is called viscosity index. This is a number that indicates the rate of change of viscosity for a given temperate range. Again, generally the higher the number the better.

This property of oil is a major contributor to the life of your bearings. And although a higher second number is good, the oil also has to be robust. For example, oil tends to lose viscosity from shear, the sliding motion between close-fitted metal surfaces of moving parts such as bearings. So resistance to viscosity loss (shear stability) is necessary to enable the oil to maintain the lubricating film between those parts.

Flash Point

This is the temperature at which an oil gives off vapours that can be ignited. Flash point can be an indicator of the quality of base stock used. The higher the flash point the better (this property affects volume of oil consumed by the engine).

Base Oil

The base oil is that which is used in the formula before additives are introduced to make up the entire oil formula. Both synthetic oils and petroleum oils can be made from paraffin base oils.

Paraffin

Paraffin is recognized as the best lubricating oils and offer a number of advantages over napthenic oils. High quality 100% paraffinic oils are the best type of base oils. Both paraffin and napthenic are types of petroleum oils.

Pour Point

More of a winter issue for climates where freezing is likely. Basically, this is a number indicating a temperature level when the oil is too thick to move. The lower the pour point the better.

% Sulfated Ash

This is a measure of how much solid material is left when the oil burns. Low ash seems to promote longer valve life.