Generally speaking, different grades of internal combustion engine oils are formulated by combining agents to achieve the corresponding specification grades,  suitable base oils, viscosity index improver and other auxiliary additives. The basic combination of general multigrade engine oil is shown in the following table:

Base oil is the main raw material in the formulation of multi-grade engine oils, usually accounting for more than 80%. The viscosity and viscosity index, oxidation resistance, volatility and low temperature of the base oil itself largely determine the main properties that can be achieved by the lubricating oil. Early mineral oils, i.e. group I base oils, were prepared by atmospheric distillation, vacuum distillation, refining, dewaxing, supplementary dewaxing and other processes of crude oil, and the viscosity index was usually between 80-120. The group II base oil and the group III base oil have undergone hydrotreatment and hydroisomerization treatment respectively, and have better viscosity index, oxidation resistance, thermal stability and low temperature performance than the group I base oil. In the engine oil formulation, viscosity is an extremely critical indicator, for multi-grade engine oils, due to the need to meet a certain viscosity requirements at high temperatures and start-up performance at low temperatures, one base oil is usually difficult to meet the requirements, usually several base oils with different viscosities are used in conjunction with each other, and a certain amount of viscosity index improver needs to be added.

Viscosity index improvers are usually one of the indispensable and important raw materials in engine oil formulations, except for single-grade oils, viscosity index improvers are generally not added. As the name suggests, this kind of agent is used to improve the "viscosity index" of the oil, and the usual dosage is 5%-10%. In short, it enhances the viscosity and temperature performance of the oil, which is mainly used for the modulation of multi-stage engine oil, and the main thing to investigate the performance of the viscosity index is viscosity, shear stability and low temperature.

According to the article "Trends in Shear Stability of Automotive Engine Oils" from the Institute of Materials, the shear stability of the viscosity index is particularly important due to the destruction of the structure of the viscosity index improver in a high-shear environment, FISST and Kurt Orbahn of 90 cycles Diesel nozzle high shear bench tests to simulate and test permanent viscosity loss are well correlated with the actual situation.

At present, the mainstream viscosity index agent in the market mainly has the following structural types: ethylene propylene copolymer (OCP), polymethacrylate (PMA), isoprene styrene copolymer (HSD), the three configurations of viscosity index agent are different in terms of viscosity, shear stability and low temperature performance, etc., and have their own characteristics, among which in the shear stability of the lubricating oil in a very important position, the HSD Type of the viscosity index agent is more excellent, and it is more suitable for the preparation of high-grade passenger car oil.

Generally, the formula composition of multi-grade engine oil is not complicated, but if you want to modulate high-grade long-span multi-grade oil products, in addition to choosing the base oil and additive packages of regular channels, the selection of viscosity index improver is equally important, in addition to meeting the specification level and quality requirements, but also to consider the economic problem of the formula, only in this way, we can modulate a product with excellent performance and can be widely accepted by the market.

(Due to the limited level of the author, it is inevitable that there will be omissions or errors, and readers are expected to correct them.)