Synthetic oil is a lubricant consisting of chemical compounds which are artificially made (synthesized) from compounds other than crude oil(petroleum). Synthetic oil is used as a substitute for lubricant refined from petroleum, because it generally provides superior mechanical and chemical properties than those found in traditional mineral oils.
Dr. Hermann Zorn of I.G. Farben Industrie in Germany actually began to search for lubricants with the properties of natural oils but without the tendencies to gel or gum when used in an engine environment. His work led to the preparation of over 3500 esters in the late 1930s and early 1940s including diesters and polyol esters and banana oil. During the same time period in the United States, Dr. W.A. Zisman working at the Naval Research Laboratory (NRL) was also synthesizing esters, especially diesters.
Comparison of the viscosimetric properties of ester- and polyglycol-based engine oils in WWII and in 1973 at Renault/ELF. SS stands for “Synthetischer Schmierstoff,” synthetic oil.
The first real synthetic engine oils appeared for aircraft engines in WW II in Germany and in the United States of America (USA). The motivation in Germany may be primarily related to resource issues, but also to functional performance requirements. The base oils for aircraft engines in Germany were based on a blend of an adipic acid ester with a poly(ethylene) oil e.g. polymerized olefins/ethylene. Easing engine starts in winter and avoiding soot deposits in the oil radiator were two of the drivers of the US Air Force., to apply from March 1944 polyglycols (polypropylene glycol monobutylether).
Synthetic engine oil
In the mid 1960s Chevron U.S.A was the first to market and produce a complete range of 100% syntheticPolyalphaolefins based lubricants, which began to be marketed as a substitute for mineral oils for enginelubrication. Although in use in the aerospace industry for some years prior, synthetic oil first became commercially available in an American Petroleum Institute (API)-approved formula for automobile engines when standards were formalized for synthetic-based lubricants.
Other early synthetic motor oils marketed included “The Original Syn!” by SynLube in 1969, NEO Oil Company (formally EON) in 1970, which were dibasic acide esters, or diesters, and polyol esters-based synthetic lubricants. In 1971 All-Proof, now called Red Line, introduced a synthetic oil, followed fourth by Amsoil who packaged and resold a diester-based 10W40 grade from Hatco in 1972, and then Mobil 1, introduced in North America in 1974 (with a PAO-based 5W20 grade).
Synthetic base stocks
Synthetic motor oils have been made from the following classes of lubricants:
- Polyalphaolefin (PAO) = American Petroleum Institute (API) Group IV base oil
- Synthetic esters, etc = API Group V base oils (non-PAO synthetics, including diesters, polyolesters, alklylated napthlenes, alkyklated benzenes, polyglycols etc.)
Other base stocks help semi-synthetic lubricants
Group II and Group III type base stocks help to formulate more economic type semi-synthetic lubricants. Group I, II, II+ and III type mineral base oil stocks are widely used in combination with additive packages, performance packages, ester and/or Group IV polyalphaolefins in order to formulate semi-synthetic based lubricants. Group III base oils are sometimes considered as synthetic but they are still classified as highest top level mineral base stocks. A Synthetic or Synthesized material is one that is produced by combining or building individual units into a unified entry. Synthetic base stocks as described above are man-made and tailored to have a controlled molecular structure with predictable properties, unlike mineral base oils which are complex mixtures of naturally occurring hydrocarbons.
- Hydrocracked/Hydroisomerized = API Group III base oils. Chevron, Shell, and other petrochemical companies developed processes involving catalytic conversion of feed stocks under pressure in the presence of hydrogen into high quality mineral lubricating oil. In 2005 production of GTL (Gas-to-liquid) Group III base stocks began. Even though they are considered a synthetic product they are still mineral base stocks and counted as the mineral part of all semi-synthetic lubricants. Group III base stocks [with certain amount of mixture of PAOs and esters and Group V] are considered synthetic motor oil ONLY in the United States. Group III based lubricants are not allowed to be marketed as “synthetic” in any market outside of the USA.
The technical advantages of synthetic motor oils include:
- Measurably better low and high temperature viscosity performance
- Better chemical & shear stability
- Decreased evaporative loss
- Resistance to oxidation, thermal breakdown and oil sludge problems
- Extended drain intervals with the environmental benefit of less oil waste.
- Improved fuel economy in certain engine configurations.
- Better lubrication on cold starts
The disadvantages of synthetic motor oils include
- The lower friction may make them unsuitable for break-in (i.e. the initial run-in period of the vehicle) where friction is desirable to cause wear. Improved engine part machining has made break-in less critical than it once was though. Many modern cars now come with synthetic oil as a factory fill.
- Potential decomposition problems in certain chemical environments (industrial use dominantly)
- Potential stress cracking of plastic components like POM (polyoxymethylene) in the presence of PAOs (polyalphaolefins).
- Potential on some older pushrod race engines with roller lifters for the roller itself not to spin with camshaft movement, but rather slide while the roller itself remains either stationary or at a lower circumferential speed than that of the camshaft lobe.
- Synthetics do not hold lead in suspension as well as mineral oil, thus caution is advised when the engine is run on leaded fuel. As an example, leaded fuel is still commonly used in aviation (avgas).
- In July 1996, Consumer Reports published the results of a two year motor oil test involving a fleet of 75 New York taxi cabs and found no noticeable advantage of synthetic oil over regular oil. In their article, they noted that “Big-city cabs don’t see many cold start-ups or long periods of high speed driving in extreme heat. But our test results relate to the most common type of severe service — stop-and-go city driving.” According to their study, synthetic oil is “worth considering for extreme driving conditions: high ambient temperatures and high engine load, or very cold temperatures.”  This research was criticized by some because most engine damage appears to be caused by cold starts, and their research method may not have included enough cold starts to be representative of personal vehicle use.
- Synthetic oils are not recommended in automotive rotary engines.
Semi-synthetic oils (also called ‘synthetic blends’) are blends of mineral oil with no more than 30% synthetic oil. Designed to have many of the benefits of synthetic oil without matching the cost of pure synthetic oil. Motul (company) introduced the first semi-synthetic motor oil in 1966.
Lubricants which have synthetic base stocks even lower 30%, high performance additive packs consisting of esters can also be considered as synthetic lubricants. Ratio of the synthetic base stock is generally used to define commodity codes among the customs declarations of tax purposes.