A PRIMER ON SYNTHETIC OIL
A number of synthetically made oils are available that give better performance than those made from crude oil. They are better at reducing friction and engine wear, have good detergency properties which keep the engine cleaner, offer less resistance for moving parts, and require less pumping power for distribution. With good thermal properties, they provide better engine cooling and less variation in viscosity. Because of this, they contribute to better cold-weather starting and can reduce fuel consumption by as much as 15%.
These oils cost more than those made from crude oil. However, they can be used longer in an engine, with (3,000-5,000 miles) being the oil change interval suggested by most manufacturers. Synthetic motor oils are produced from feedstocks other than naturally occurring petroleum. Many types of synthetic oils have been developed, but those used in motor oils are derived from petrochemicals or lipochemicals (animal and vegetable oils).
Extensive work on synthetic lubricants began in the 1930s. Germany was forced to develop synthetic lubricants because of a shortage of crude petroleum. The synthetic lubricants helped solve operational problems with gas turbines and were adopted for jet engine use in the 1950s.
After further development, synthetic motor oils were introduced for automotive use in the 1970s. The most common base for synthetic motor oils for automotive use is polymerized alpha olefins (PAO). The PAO base is synthesized from olefinic hydrocarbons by controlled polymerization. Thus, the resulting fluid is composed entirely of hydrocarbons of similar molecular structure. The properties of the PAO can be controlled by careful selection of the correct olefins and careful control of the polymerization process.
The resulting PAO is almost entirely paraffinic and contains no sulphur, nitrogen, or metallic impurities. Esters are the second most common base for synthetic motor oils. An ester can be formed by the chemical reaction of an alcohol with a fatty acid. Fatty acids are obtained from animal fats or vegetable oils. Diesters, containing two fatty acids for each alcohol, appear to be more suitable than monoesters for use in synthetic motor oils.
Typically, a synthetic motor oil contains a mixture of base stocks, such as PAO and an ester fluid. Such an oil has a very high viscosity index. For example, a multigrade range of SAE 5W-20 can be obtained without adding a viscosity index improver. Usually, the synthetic motor oils cost two or three times more than conventional motor oils. With conventional motor oils in abundant supply, the synthetic motor oils must show clear advantages to gain acceptance.
The following are among the advantages of synthetic motor oils:
· extended drain intervals [for example, up to (35,000 miles) between oil changes in automobiles],
· cold weather starting because of low oil viscosity,
· cleaner running engines, and
· maintenance of higher oil pressure at hot idle because of high viscosity index.
By definition, synthetic oil contains essentially no mineral oil. Blends of synthetic-base stocks and mineral oil are, by definition, semi-synthetic oils. The semi-synthetic oils are less expensive than synthetic oils and are available commercially, but do not have the same benefits as "full" synthetics.
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