1. Synthetic Oils

LO 10-04: Describe the composition of synthetic oil and outline the advantages and disadvantages of synthetic oil.

 

Synthetic Oils

Synthetic-base lubricants have been used in jet engines and special-purpose engines since World War II. Tanks used in World War II needed synthetics to allow the oil to properly lubricate the engines in extreme cold while jet engines needed synthetics to handle high operating temperatures that would burn petroleum-based oils. Synthetic lubricants did not begin to make in-roads into automotive applications, however, until the late 1970s.

The term synthetic oils generally refers to oils with a synthetically derived or manufactured base stock. While some brands of synthetic oils are derived from ultra-refined petroleum oil, the most popular base stock for synthetic oil is created from a petroleum-derived molecule called polyalphaolefin (PAO; TABLE 10-3) . PAO molecules are smaller and more consistent in size, and no impurities are found in this oil because it is derived through a chemical process, making it chemically stable and flexible compared to conventional oil Figure 24. Approximately 70% of the base stock of synthetic oils is made from PAO. Chemical additives are then blended with the synthetic oil base stock, similar to the process of making conventional oils. However, synthetic oils usually have more additives than conventional oils. No API or SAE standards exist yet for defining what synthetic oil is; however, they do need to meet minimum API and SAE criteria if they carry the API symbols.

   Fig10_24

FIGURE 10-24: Comparing the size of conventional mineral oil and synthetic oil molecules.

 

  TABLE 10-3: Sources of Base Stock Lubrication Oil  
Oil Base Stock Disadvantages Column 3
Conventional mineral oil Mineral oil derived from crude oil Contains undesirable impurities, such as oxygen, sulfur, nitrogen compounds, trace metals, and carbon residues. Additive package cannot operate effectively because the additive has to compete with the impurities when bonding with base oil molecules. These oils break down under extreme heat and form solids under extreme cold.
Hydro-processed mineral oil Highly refined mineral oil Contains some undesirable chemical impurities but is more refined than conventional mineral oil.
Severe hydro-processed mineral oil (considered synthetic in North America only) Ultra-refined mineral oil (may be also blended with PAO to make semi-synthetic oils) Requires additional processing and removal of more impurities than hydro-processed mineral oil, but some impurities still exist.
Fully synthetic oil (chemically derived) Chemically manufactured (PAO) Expensive

 

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