What is multigrade lubricating oil?

December 17, 2023

What is multigrade lubricating oil?

Multilevel lubricating oil is a kind of lubricating oil with good viscosity and temperature performance, wide working temperature and obvious energy-saving effect. In IS01989/1 "Petroleum Industry terminology -1", multigrade oil is defined as: the difference between the W viscosity level and the 100oC kinemical viscosity level of a multigrade lubricating oil is at least 15. Specifically, the multigrade oil contains both a W viscosity grade and a 100oC kinematic viscosity grade, and the difference between the two viscosity grades is at least 15.

An oil marked with only one viscosity grade or with two viscosity grades, but with a difference of less than 15, is called a single grade oil. For example; 30 oil, 40 oil, etc.; Another example is 20/20W oil, the oil meets the requirements of 20 and 20W viscosity grade oil at the same time, but the difference between the two viscosity grades is 0, so it is not a multistage oil, a single grade oil.

The difference between multigrade lubricating oil and single-grade lubricating oil mainly lies in the different viscosity-temperature characteristics. Viscosity temperature characteristic is the performance of lubricating oil viscosity changes with temperature, viscosity characteristics are usually expressed by the viscosity index in the world, viscosity index is a relative value obtained by comparing with the degree of standard oil viscosity changes with temperature. Its value is calculated by the formula of 100℃ and 40℃ viscosity of the oil. The higher the viscosity index value, the better the viscosity-temperature property of the oil. Multigrade lubricating oil viscosity index is usually more than 130, while single-grade lubricating oil is generally 75 to 100.

The operating temperature range of automotive engine oil is very wide, the minimum oil temperature when the engine starts, the difference between winter and summer is tens of degrees, and the starting oil temperature is more different from the maximum oil temperature when the load is running. If the viscosity of the lubricating oil is too large, the fluidity and pump transmission is poor, it will cause the engine to start difficult or the lubricating oil is sent to the lubricating part for too long after starting, which is easy to cause dry friction and accelerate the wear of the parts. The test shows that the wear of the engine when starting the car in city operation accounts for about 2/3. On the other hand, when the temperature is high, the viscosity of the lubricating oil is too small, which is not conducive to the formation of fluid lubricating oil film and increase friction and wear, and even cause adverse effects such as scratches and cylinder pulling.

Multigrade lubricating oil is made by adding viscosity index agent (or viscosifier) to low viscosity Base Oil, which is a major technical breakthrough to solve the problem of low temperature starting and improve the lubrication performance. Because the viscosity index agent is composed of some linear polymer organic compounds with anti-shear properties, they are dissolved in the lubricating oil, expand and expand at high temperature, increase the resistance between the lubricating oil molecules, so that the viscosity of the lubricating oil does not decrease too much, maintain a certain viscosity, form a certain thickness of the oil film, and play a due lubrication role. At low temperatures, these organic compounds curl and shrink and are suspended in the lubricating oil, and the resistance between the lubricating oil molecules is reduced, so that the viscosity of the lubricating oil will not increase too much, so as not to cause difficulty in starting the engine and increase wear.

Therefore, the multi-stage lubricating oil has good viscosivity and temperature characteristics, which is conducive to lubrication under high and low temperature conditions, and is conducive to low temperature starting, and has good anti-friction and energy saving effects. It has been proved by foreign tests that the viscous resistance can be reduced by 20% ~ 45% when using multistage oil compared with single stage oil. Domestic tests have proved that the multi-stage oil of the engine with various viscosity grades is 1% ~ 3% more fuel efficient than the single stage oil. The combined use of multigrade engine oil and multigrade Gear Oil is 2% to 4% more fuel efficient than single grade oil. It also has a good anti-friction effect.

Multigrade lubricants are easier to start than single-grade lubricants when the ambient temperature is low in winter. At ambient temperature, the engine should reach a minimum speed to start, which is called the critical starting speed. In the cold winter, the temperature is very low, the critical speed of the engine should be increased, because the kinematic viscosity of the engine oil increases greatly at low temperatures, and the resistance that needs to be overcome also increases. Therefore, when the engine is cold starting, the smaller the kinematic viscosity of the lubricating oil, the greater the engine speed, the better the cold starting performance of the engine. The dynamic viscosity of multistage oil at low temperature is much smaller than that of single-stage oil, and it is easy to start.

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