Description of Synthetic Motor Oil
Synthetic motor oil is produced from non-petroleum and petroleum chemical compounds. The molecules of hydrocarbon are uniformly
distributed, producing a base that has good properties at extreme low and high temperatures. Synthetic oil does not contain contaminants like paraffinnic waxes, which are present in crude oil. Shelf life of synthetic motor oil basically depends upon the chemical compounds and additives being used and the storage environment.
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Shelf life of synthetic motor oil is dependent upon the additives and the environmental conditions. The motor oil quality may deteriorate, and sludge may be formed, if moisture is introduced into the oil due to condensation or mishandling. Water reacts with the oil additives to produce insoluble substances that reduce the oil shelf life. Moisture may also encourage microbial growth in the lubricants.
It is recommended that the storage temperature should be stable. Generally, temperatures below 0ºF or above 100ºF will cause oil degradation, with reduced lubrication capability. Extreme low temperatures may form sediments, and separation of additives. Manufacturers normally recommend an environmental temperature between 40 degrees and 85 degrees Fahrenheit. The presence of contaminants in the environment like dust may degenerate the motor oil quality.
Therefore, if the oil can is not opened, the oil may be serviceable for long durations. Finally, the shelf life is also influenced by the product design. Elements like copper and iron can act as catalysts to promote the process of oxidation, and consequently reduce the shelf life.
Additives to Prolong Shelf Life
Several additives are added to synthetic motor oils to increase their shelf life, produce stable oil that will maintain proper viscosity and will flow correctly at low temperatures, and meet other test parameters at a wide temperature range. They improve these characteristics:
- A decrease in viscosity makes the oil unable to protect the engines from close metal contact, due to which wear is increased. Additives are used to improve the viscosity that is preserved for longer durations during the shelf life. This unit of viscosity is SUS, and its maximum recommended limit of deviation is plus or minus 15%. Viscosity determines the oil flow ability. It is the property to improve and preserve a particular quantity of sheering stress, and offer flow resistance. Thin oils have low viscosity while thick oils have high viscosity. This is a vital oil characteristic, since oil that has an extremely low viscosity may shear and cause the film strength to be reduced excessively at higher temperatures. Oils with extremely high viscosity may not reach distant components at lower temperatures, or the oil film may be torn at high RPM.
- Pour point depressants are used to decrease the freezing point of oils.
- Dispersants and detergents assist in keeping the oil clean and avoiding the formation of sludge. Contaminants are suspended in oil due to the use of dispersants.
- Oxidation inhibitors preserve the stability of oil.
- Rust and corrosion inhibitors are used for protection against condensation.
- Defoamants prevent foaming of the oil.
- Alkaline additives are used for the neutralization of acids. This characteristic is measured in Total Base Number (TBN). Oils with greater value of TBN will provide better acid neutralization. Most car motor oils are produced with TBN of 4 to 8.
- Calcium additives are added for protection from oxidative failure and also to prevent the development of varnish and sludge.
The storage environment of oil and storage techniques can significantly affect the shelf life of oils. Generally, a dry and clean space with a stable and fair temperature, with suitable racks, will increase the shelf life. A dusty and humid atmosphere with irregular temperatures will seriously affect the estimated shelf life.
The manufacturers recommend the oil shelf life based upon the additives used for each type of their product. For example, oil lubricants that include rust inhibitors can lose their functional capabilities in a short time of storage. The oil stored should be rotated to ascertain that the recommended storage life is not inadvertently exceeded.
Most producers supply a suggested storage practice to increase the oil shelf life. Temperature variation may move air in the environment causing thermal siphoning of the container. Movement of air is increased in a container that is not completely full and has more vacant space. Although the barrel is sealed properly and oil does not seep out, a firm container still draws in air with a drop in temperature, and blows it out with a rise in temperature. Contaminants and moisture come into the oil, along with air that leads to degradation of additives and oil base. Water condensation may occur in the drum, with water layer being formed at the bottom that is pumped to the engine.
Extreme cold or hot temperatures can produce chemical degradation. Rust inhibitors that are added may lose their functional capability soon after a short storage period. A humid environment is detrimental to oil storage since moisture degrades the additives in a short period, and expedites the process of base stock oxidation. Shelf life of synthetic motor oil can be improved significantly if the recommendations of the manufacturers are followed strictly.
- Mobil Oil – Shelf life for engine oils
- AMS Oil – Factors that can influence the shelf life of motor oils