The methods for determining shear stability include ultrasonic method, diesel nozzle method, gear method, and direct measurement with an engine (L-38), among others. In the ultrasonic method, the viscosity loss caused by ultrasonic shear action on the test oil in the energy concentrator (i.e., ultrasonic oscillator) is measured, and the shear stability is evaluated based on the viscosity drop rate of the oil. At the beginning of the test, standard oil is selected to work under standard shear test conditions for 15 minutes, adjusting the viscosity drop rate to the specified range. Then, the cup containing the test oil is placed in a water bath at a predetermined temperature, and the energy concentrator is immersed in the test oil, maintaining a constant temperature for 10 minutes. The power switch is turned on, and the frequency is adjusted to achieve resonance. After shearing for the specified time, the viscosity drop rate of the test oil is measured. A large viscosity drop rate indicates poor shear stability of the lubricant.

When lubricating oil circulates in the engine, it is subjected to mechanical shear, which breaks the high molecular weight polymers in the oil, leading to a decrease in viscosity and affecting the normal lubrication of various engine components. Additionally, it can impact fuel consumption, energy saving, and environmental protection. Multi-grade internal combustion engine oils are formulated with a certain amount of composite additives and high molecular weight polymers with strong anti-shear properties to ensure low-temperature fluidity and high-temperature viscosity retention. This allows the lubricating oil to maintain its viscosity within the original grade requirements even after shearing under certain conditions in the engine, thus preventing permanent viscosity failure of the engine oil and adverse effects on the engine.

Determining the quality of oil based on the color of the engine oil is a common practice among users. The color of the oil can sometimes reflect quality issues, but it is not the only criterion for assessing oil quality. The initial color of the engine oil depends on the color of the base oil and additives. Therefore, using color to determine the quality of lubricating oil is no longer appropriate. Generally, the color of base oils does not vary significantly, and the initial color of the engine oil is mainly determined by the depth of the additive color. Different manufacturers may use different colors of additives for oils of the same grade, which generally does not indicate the quality of the engine oil.

The various lubricating oil components obtained from vacuum distillation contain undesirable components such as oxides, sulfides, colloidal substances, and asphaltenes, which must be removed through refining. The refining processes include acid-base refining, deep agent refining, propane deasphalting, bleaching clay refining, and hydrogen refining. These refining processes use larger amounts of bleaching clay and solvents, and through more refining cycles, they remove more non-ideal components from the base oil, significantly improving the comprehensive properties of the lubricating oil, such as viscosity-temperature performance and oxidation resistance. This process is called deep refining of lubricating oil.

Mineral lubricating oil base oil is also known as neutral oil. The viscosity grade of neutral oil is expressed in Saybolt viscosity (seconds) at 37.8℃ (100F), marked as 100N, 150N, 500N, etc.; while high viscosity oil derived from residual oil is called bright oil, expressed in Saybolt seconds at 98.9℃ (210F), such as 150BS, 120BS, etc. Since the 1970s, China has established three standards for neutral oils, namely paraffinic neutral oil, intermediate base neutral oil, and low pour point naphthenic neutral oil, marked as SN, ZN, and DN respectively. For example: 75SN, 100SN, 150SN, 200SN, 350SN, 500SN, 650SN, and 150BS. However, the viscosity of SN oil is classified by kinematic viscosity at 40℃, while BS is classified by kinematic viscosity at 100℃.

The color determination method for petroleum products in our country divides the color of petroleum products into 16 color codes. The colors deepen sequentially from 1.0, 1.5, 2.0... with the darkest color being 8.0. The color of lubricating oil ranges from light yellow to dark brown, and the depth of color depends on the amount of colloidal content in the oil; the more colloid is removed, the lighter the color. Therefore, color can be used as an indicator of the refining depth of base oil. However, in finished lubricating oil, various additives are added, many of which have color.

It refers to the determination of the corrosive effects of organic acids and bases in oil products on metals under specified conditions, to assess whether lubricating oil contains substances that can corrode metals. The corrosion tests for hydraulic oil and gear oil use copper sheets as test pieces, and the test level is determined based on the discoloration of the copper sheets. The anti-corrosive ability of internal combustion engine oil is evaluated using engine bench tests—high-temperature oxidation and bearing corrosion assessment method (L-38 method).

This refers to a test where a steel rod is immersed in a mixture of a sample with distilled water or synthetic seawater under specified conditions for a designated period, after which the degree of rust on the steel rod is visually assessed. This method is used to evaluate the rust prevention capability of oils such as turbine oil, hydraulic oil, and gear oil when mixed with water on iron components.

The base oil from the same manufacturer may come from several places, meaning that the production batches of base oil from the same origin are different, and there are also differences in color. Therefore, it is normal for engine oil from the same manufacturer to have different colors on different production dates.

Under external force, the volume of liquid is not easily changed, but when air is mixed into the liquid, it will affect its compressibility. Maintaining the incompressibility of hydraulic oil is crucial for reliably transmitting energy as a working medium and ensuring the sensitive operation of control mechanisms. Currently, most hydraulic oils used are petroleum-based, and air can dissolve in oil, with its solubility mainly depending on air pressure and temperature. When air remains dissolved in the oil, the hydraulic system does not encounter problems. However, when hydraulic oil passes through cylinders, valves, or other hydraulic components, the pressure may suddenly drop, and combined with the effects of temperature changes, air can easily be released from the oil and form many bubbles, which will affect the incompressibility of the hydraulic oil. Additionally, during the operation of hydraulic system components, the hydraulic oil and air can easily generate foam due to mechanical agitation. If the foam does not dissipate quickly, it will also lead to a decline in the working performance of the hydraulic oil. Therefore, to ensure that hydraulic oil has good incompressibility and anti-foaming properties, measures must be taken to prevent air from mixing into the hydraulic system, and anti-foaming agents should be added to enhance the anti-foaming performance of the hydraulic oil. The incompressibility of hydraulic oil is evaluated using the air release value. Poor air release of hydraulic oil can lead to a series of mechanical failures. After hydraulic oil is compressed in the hydraulic system, during the transition from high pressure to low pressure, the air in the oil cannot be released, and the color of the hydraulic oil will change significantly, resembling the color of emulsified oil, appearing milky white, which can create a misconception. The air release value of hydraulic oil is defined as the time (min) required for the air carried in the oil to reduce to a specified amount at 50°C. The air release value is measured according to SH/T 0308-92 "Method for Determining the Air Release Value of Lubricating Oil." The anti-foaming property of hydraulic oil, also known as foaming tendency, refers to the tendency of the oil to generate foam and the stability of the generated foam. It is generally expressed in terms of foam tendency/stability (mL/mL) under certain conditions. The foaming property of hydraulic oil is measured according to GB/T 12579-90 "Method for Determining the Foaming Characteristics of Lubricating Oil."

Different engines have different requirements for oil pressure (specific pressure data can be found in the "Engine Lubrication System Parameters Table"). If the pressure is within the range required by the engine manufacturer, it is considered normal and can meet the lubrication needs for the engine to operate properly.