The speed of bubble separation is referred to as air release property (abbreviated as degassing property). If the oil product has poor degassing property, air separates from the oil slowly and remains in the oil for a long time. The retention of air in the oil significantly increases the compressibility of the oil, causing delayed transmission response, reducing the accuracy of the hydraulic system, and leading to control system failure. Under high pressure, it gets compressed, and under low pressure, it suddenly expands, causing strong vibrations and increased noise in the machinery. It reduces the density of the oil, increases the viscosity of the oil, resulting in poor driving of the hydraulic system, and at temperatures below 0°C, it worsens the starting performance of hydraulic devices. It accelerates the oxidation rate of the oil, leading to the formation of precipitates, accelerating the corrosion and wear of mechanical system parts, while also shortening the service life of the oil itself. It reduces the efficiency of the equipment. To avoid the above adverse phenomena, hydraulic oil is required not only to have good anti-foaming properties but also to have good air release properties.

Emulsification resistance refers to the ability of lubricating oil to resist the emulsification of water with oil. Lubricating oil should not contain water. If water enters the oil, it will cause the emulsification phenomenon of the engine oil. This disrupts the continuity of the lubricating oil film, preventing the friction pair from receiving adequate lubrication. At the same time, it causes the lubricating oil to become acidic, affecting its performance, leading to deterioration, and shortening its service life. The emulsification resistance test of lubricating oil is to detect the emulsification resistance performance of the lubricating oil. In the test, 40 milliliters of oil and 40 milliliters of distilled water are mixed in a test tube, heated to 54°C, and shaken on an instrument to completely blend the oil and water into an emulsion. Then, the state is observed, and timing begins. At this point, the oil and water gradually separate, and when the separated water reaches 37 milliliters, timing stops. The duration of this time is the emulsification resistance. The time for the separated water should not exceed 30 minutes; otherwise, it is considered unqualified. The emulsified layer should also not exceed 3 milliliters.

Anti-foaming property indicates the size of the foam volume generated when the oil is exposed to air or stirred, as well as the speed of defoaming, among other characteristics. In the technical standards for petroleum products, anti-foaming property is represented by the milliliters of foam tendency/stability at three temperature conditions: 24°C, 93°C, and then 24°C again. The smaller the value, the better the anti-foaming property of the lubricant. Under specified conditions, the lubricant is first mixed with water to form an emulsion, and then the time (in minutes) required for the lubricant and water to completely separate is recorded at a certain temperature. The shorter the time, the better the demulsification performance. The lubricating effect of lubricating oil on machinery is indisputable. However, if the foam content in the lubricating oil exceeds the specified physicochemical indicators, the surface tension of the foam will disrupt the continuity of the oil film, preventing proper lubrication of the machine surfaces and causing mechanical wear. Especially when the engine is running, the oil is subjected to intense agitation, and air is mixed into the oil, forming foam. On one hand, foam reduces the sealing effect of the oil and can create an insulating layer that decreases heat dissipation. In severe cases, it can cause the oil pump to run dry, leading to gas blockage in the oil circuit, interrupting oil supply, and preventing lubrication of the engine friction pairs, resulting in mechanical accidents. The anti-foaming test is used to verify whether this physicochemical indicator meets the standards. 150/10 indicates that the foam tendency (foam volume) in the test results does not exceed 150 milliliters; stability (foam volume) does not exceed 10 milliliters. The smaller the numbers, the better the anti-foaming property of the lubricant.

The ability of oil products to resist the action of air or oxygen, leading to permanent changes in their properties, is called the oxidation stability of the oil products. During storage and use, it is inevitable that oil products will come into contact with air and oxidize. The longer the contact time and the higher the temperature, the deeper the degree of oxidation, causing some properties of the oil products to undergo irreversible changes, such as increased acid value, increased viscosity, increased sediment, and darker color, etc. These changes significantly shorten the service life of the oil products. The oxidation stability of oil products is closely related to the properties of the base oil used, the depth of refining, the characteristics and quality of additives, compatibility, and formulation processes.

The black residue formed after the oil product is heated, evaporated, and burned under specified test conditions is called carbon residue. Carbon residue is an important quality indicator of base oil for lubricants and is a specified item for assessing the properties and refining depth of lubricating oil. The amount of carbon residue in the base oil for lubricants is related not only to its chemical composition but also to the refining depth of the oil product. The main substances that form carbon residue in lubricating oil are: colloids, asphaltenes, and polycyclic aromatic hydrocarbons in the oil. These substances decompose and condense under conditions of insufficient air, forming carbon residue. The deeper the refining depth of the oil product, the smaller its carbon residue value. Generally speaking, the smaller the carbon residue value of the blank base oil, the better.

The acid value is an indicator of the presence of acidic substances in lubricating oil, measured in mg KOH/g. Acid values are divided into strong acid value and weak acid value, and their combination is referred to as total acid value (abbreviated as TAN). What we commonly refer to as "acid value" actually means "total acid value (TAN)". The base value indicates the presence of basic substances in lubricating oil, also measured in mg KOH/g. Base values are similarly divided into strong base value and weak base value, and their combination is referred to as total base value (abbreviated as TBN). What we commonly refer to as "base value" actually means "total base value (TBN)". The neutral value actually includes both total acid value and total base value. However, unless otherwise specified, the term "neutral value" generally refers only to "total acid value", which is also measured in mg KOH/g.

Mechanical impurities refer to the precipitates or gel-like suspensions present in lubricating oil that are insoluble in solvents such as gasoline, ethanol, and benzene. Most of these impurities are sand, gravel, and iron filings, as well as some organic metal salts that are difficult to dissolve in solvents due to additives. Generally, the mechanical impurities in the base oil of lubricating oil are controlled to below 0.005% (a level below 0.005% is considered negligible). However, for some oils with a large amount of additives, the mechanical impurity index may be slightly higher. This is because after adding various additives, there may be some insoluble substances, and these gel-like metal organics do not affect their performance. Therefore, one should not simply judge the quality of oil based on the size of mechanical impurities; the nature and category of the impurities should be analyzed.

The freezing point indicates the temperature at which a liquid freezes, and it is primarily an important indicator for measuring the low-temperature flow of antifreeze.

The equilibrium reflux boiling point refers to the temperature at which boiling occurs under atmospheric pressure conditions within a condensing reflux system. The equilibrium reflux boiling point is one of the important indicators of brake fluid; if it is too low, the brake fluid is prone to evaporation and can cause gas blockage. Many vehicles experience deteriorating braking performance while driving, leading to safety accidents, often related to the brake fluid's failure to meet the standard equilibrium reflux boiling point. When selecting brake fluid, it is essential to purchase products from reputable manufacturers, especially ensuring that the equilibrium reflux boiling point is above 200°C.

The dropping point refers to the temperature at which grease softens and drops from the grease cup when heated under specified conditions. The dropping point of grease can roughly be used to measure its maximum operating temperature range.