Oil Classification (Automobile)

11.8.

Oil Classification

IC Engines.

The American Petroleum Institute (API) has been largely responsible for the classification of engine oils in relation to engine service requirements. Several tests have been conducted to arrive at the various oil classification and some of them are as follows,
(i) Low-temperature rust test.
(«) Low-temperature engine deposits test.
(Hi) High-temperature oxidation resistance test.
(iv) High-temperature deposits and sludge test.
(v) Engine scuffing and wear test.
(vi) Engine cleanliness test.
(vii) Bearing corrosion test.
The classification for engine oil that are primarily intended for gasoline engines are listed in Table 11.1 and that for diesel engines in Table 11.2.

Synthetic Oil.

Most synthetic oils are made from a petroleum or crude oil base stock. The differences between most conventional oils and synthetic oils are in the refining process and the additives used. When conventional oils are refined, the molecular structure of the crude oil is not changed. However, for manufacturing the synthetic oil smaller molecules from the crude oil are combined with molecules from other sources to make the larger molecules of the synthetic oil. Additives in the synthetic oils, which are usually more than that in conventional oils, are then blended with the synthetic stock. Additional energy is used in the preparation of synthetic oils and hence these oils are more expensive than conventional oils. Some of the advantages claimed by synthetic oil manufacturers are the following.
(i) Increased oil change intervals up to 80,000 km.
(ii) Reduced wear in engine parts.
(Hi) Increased fuel economy because synthetic oil provides less friction.
(iv) Improved high-temperature protection of engine parts.
(v) Easier cold-weather starting because of reduced friction.

Re-refined Oil.

Re-refined oil is used engine oil that has been recycled. Engine oils made from recycled based stock can be equivalent in performance to those made from virgin petroleum base stock, if proper quality control is given to the used oil base stock and the processing procedure. The use of re-refined oil reduces pollution from the improper disposal of used oil.

Oils for Alternative Fuels.

Some oil refiners produce oil that is specially formulated for propane or natural-gas-fueled engines. These oils have a reduced detergent and dispersant additive content because propane and natural gas have less carbon content than gasoline. When these fuels are used, the carbon deposits on pistons and piston rings are reduced, and oil with less detergent and dispersant additives may be used. If other alternative fuels such as methanol or hydrogen are used in large numbers of cars, then oils with more compatible characteristics with these fuels are to be developed.

Oil Requirements of the Future.

As new engines and engine materials are developed, and alterantive fuels are used, engine oil requirements will continue to modify. Some of the oil requirements and developments in the future are summarised as follows.
(i) Energy conservation properties for both gasoline and diesel engine oils through friction
modifiers and other additives. (H) Lower phosphorus content to protect the exhaust emission catalyst. (Hi) The use of new 5 W oils for improved cold starting and energy conservation.
(iv) Extended oil drains performance.
(v) Light-duty diesel performance.
(vi) New high-temperature viscosity evaluation methods.
(vii) The use of re-refined and synthetic oils.
(viii) Compatibility with engine seal materials and other new materials used in engine parts.
(ix) Compatibility with alternative fuels.