Why is oil precipitation more likely to occur in lubricating oil with better base oil

February 21, 2024

Why is oil precipitation more likely to occur in lubricating oil with better Base Oil

Sometimes, our lubricating oil in storage, found that there is some sediment at the bottom of the barrel, some people say that this is because the quality of lubricating oil is not good, in fact, the precipitation is a normal phenomenon, the bottom of the precipitation is an additive. Lubricants generally have additives, and in some cases, additives will precipitate, which is a normal phenomenon, such as at low temperatures, some oils will have this problem, and a small amount of precipitation is the precipitated additive.

Why do additives precipitate?

The base oil of engine oil accounts for about 90%, and the rest is additives. The quality of base oil is crucial to the performance of lubricating oil, which provides the most basic lubrication, cooling, oxidation resistance, corrosion resistance and other properties of lubricating oil. According to custom, the base oil extracted from petroleum by physical distillation method is called mineral oil, and the base oil obtained by chemical synthesis is synthetic oil.

Base oil determines the quality of lubricating oil. In the production of high-grade lubricating oil, hydrogenated base oil has good viscosive-temperature properties and sensitivity to antioxidant additives. The use of hydrogenation base oil promotes the improvement of lubricating oil quality, but with it, its solubility to additives will be relatively small.

Usually high-quality lubricating oil, with extremely high cleanliness, very small density, with excellent low temperature performance, it is necessary to ensure that the oil has a good low temperature cold start performance under extremely cold and low temperature conditions, therefore, its additives will inevitably exist a certain precipitation phenomenon, this precipitation is a normal phenomenon of high-quality oil.

According to custom, the base oil extracted from petroleum by physical distillation method is called mineral oil (some non-deep hydrogenation base oil should also be called mineral oil), and synthetic oil, as the name suggests, is the base oil obtained through chemical synthesis (most of its components are not directly present in oil).

There is no accurate definition of synthetic oil and mineral oil, which is commonly known as the statement, API(American Petroleum Institute) on the base oil is divided into five categories, usually the fourth type of base oil called synthetic oil.

Synthetic oils are usually PAO(Poly Alpha Olefin), XHVI(eXtra High ViscosityIndex), esters.

In addition, VHVI(Very High ViscosityIndex) base oils have the highest viscosity index between synthetic and mineral oils, while UHVI(Ultra High ViscosityIndex) base oils have the highest viscosity index.

In the production of high-grade lubricating oil, hydrogenated base oil has good viscosity and temperature properties, the sensitivity of antioxidant additives, and the amount is increasing. The use of hydrogenated base oil promotes the improvement of lubricating oil quality, but it also has the characteristics of low solubility to additives.

The cleanliness of the ultra-high viscosity index base oil used in the three times deep hydrogenation isomerization is not comparable to that of the general base oil, with extremely high cleanliness, very small density, and excellent low temperature performance. It is necessary to ensure that the oil has good low temperature cold start performance under extremely cold and low temperature conditions.

Therefore, the additive is bound to have a certain precipitation phenomenon, this precipitation is a normal phenomenon of high-quality oil products, in short, the oil selected base oil grade is inversely proportional to the solubility of the additive, the deeper the degree of refining of the base oil, the worse the degree of dissolution of the additive.

Therefore, if high-grade lubricating oil products precipitation phenomenon, is also a normal phenomenon, will not affect the use of lubricating oil performance.

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