Summary of Common Issues in Lubricant Use - Tips from XiaoYiChong

author: Yibuzz_XiaoYiChong

2026-01-16

Is it normal for lubricants to turn black during use?

Answer: There are three main reasons for lubricants turning black: (1) lubricant deterioration, (2) component wear, and (3) impurities entering the oil tank. If impurities have not entered the tank during use, it could indicate a quality issue with the lubricant itself, and the brand should be replaced. Slight darkening of color over time is normal, but it should not turn completely black (except for engine oil).

Can older equipment use lower-quality oil?

Answer: Generally, the wear parts of equipment are surface-treated, giving them higher surface hardness and resistance to wear, though the internal material may be softer. In older equipment, some parts may already have surface wear, so using lower-quality lubricants will accelerate wear. It is recommended not to use lower-grade or poor-quality lubricants.

Why can't other oils replace gear oil?

Answer: Some users substitute gear oil with anti-wear hydraulic oil, slideway oil, turbine oil, or general machinery oil, which is incorrect. The entire machine's power is transmitted through gear mechanisms, where the meshing surfaces endure enormous loads, requiring lubricants with extreme pressure properties. Other oils lack extreme-pressure additives and cannot protect gear surfaces, leading to pitting, fractures, and other damage.

Can gear oils of the same viscosity be interchanged?

Answer: No. Although they may have the same viscosity, gear oils differ in grade. Heavy-duty gear oil can replace light-duty gear oil, but not vice versa. Most domestic gear oils are medium or lower load grades and are unsuitable for high-speed and high-load equipment.

What causes lubricants to turn white?

Answer: Lubricants generally turn white due to water entering the oil tank, causing emulsification. To prevent this, ensure water does not enter the tank or open oil drums. Check equipment seals for damage, inspect for water in the tank during oil changes, and store oil drums in dry areas.

Is it okay to use any oil as long as the equipment has oil?

Answer: Proper lubricant use is crucial. Lubricants are like the lifeblood of machinery, and poor-quality oil can damage expensive equipment. Different lubricants contain specific additives to meet the needs of various parts of the equipment (e.g., antioxidants to prevent oxidation, rust inhibitors to prevent rust, and anti-wear agents to prevent wear).

Can used lubricants be reused after sedimentation?

Answer: Some users reuse oil after sedimentation, which is inadvisable. After use, the performance of the oil deteriorates, making it equivalent to using substandard products.

When changing oil, can part of the old lubricant be replaced with new oil?

Answer: It is best to drain the old oil completely. Mixing used oil with new oil reduces the overall quality and shortens its service life.

How can lubricant quality be judged by appearance?

Answer: High-quality lubricants are generally light yellow, uniform, and transparent. Lubricants with higher viscosity may appear slightly darker (e.g., viscosity above 460#). If the oil is black, contains impurities, or has water, it is considered substandard.

What is lubricant viscosity?

Answer: Viscosity refers to the speed at which a lubricant flows under specific conditions. It changes with temperature. International standards often use viscosity at 40°C or 100°C as a reference.

Does higher viscosity indicate better lubricant quality?

Answer: No. Generally, parts with higher operating speeds and lower loads require lower-viscosity lubricants (e.g., spindle oil), while parts with lower speeds and higher loads require higher-viscosity lubricants (e.g., gear oil). Always follow equipment supplier recommendations, as lubricant quality involves multiple factors beyond viscosity.

What causes foaming in lubricants during operation?

Answer: Foaming is usually due to poor lubricant quality. Qualified lubricants should not produce excessive foam. Mixing different types of lubricants can also cause foaming, so avoid mixing oils with different properties.

What does the lubricant grade number mean?

Answer: According to ISO standards, industrial lubricants are categorized into viscosity grades based on their viscosity at 40°C. Higher numbers indicate higher viscosity.

Why do lubricants with the same grade number have different viscosities?

Answer: Each viscosity grade has a range (similar to manufacturing tolerances). For example, the viscosity range for 100# gear oil is 90–110, and for 150# gear oil, it is 135–165. Oils within these ranges are considered compliant.

What is viscosity index?

Answer: The viscosity index measures the rate of viscosity change with temperature. A higher index indicates less change in viscosity with temperature. Industrial lubricants typically have a viscosity index above 90.

After the running-in period of new equipment, is it necessary to replace the lubricant?

Answer: Yes, the lubricant must be replaced! During the initial operation of new equipment, a significant amount of metal particles is generated in the lubricant, and these particles will accelerate the wear of components.

Why do new machines have a running-in period, and can inferior oil be used during this period?

Answer: Generally, during the initial usage phase of new machines, due to the impossibility of 100% precision in component machining, there will be uneven force distribution during the surface interaction of components, causing some wear—this is known as running-in wear. According to experience, most equipment suppliers specify the running-in period as one month. After this period, the interaction between components becomes smoother, and the machine operates more stably. However, due to the presence of wear particles in the lubricant, it is necessary to replace the lubricant; otherwise, these particles will continue to cause component wear, shortening the equipment's lifespan. Although the lubricant is only used for one month during the running-in period, some users mistakenly believe that any lubricant will suffice since it’s only temporary. Here, we specifically remind users: never use inferior lubricant during the running-in period.

Reasons are as follows:

1. Different parts of the machine have varying requirements for lubricant, and the running-in period does not lower the performance demands on the lubricant. On the contrary, the performance requirements are higher. During the running-in phase, due to mechanical machining errors, the impact on the surface of components is greater, necessitating a high-quality lubricant to protect the working surface from damage.

2. The running-in period only smooths out the unharmonious interactions between components, but if an inferior lubricant causes significant surface wear, the equipment's lifespan will be greatly reduced:

Generally, components undergo surface heat treatment, resulting in high surface hardness and lower internal hardness. If an inferior lubricant damages the hardened surface layer, the components will wear out rapidly.
Wear damage is irreversible; once it occurs, the only solution is to replace the component.

In summary, high-quality lubricant should be used during the running-in period, and the lubricant should be promptly replaced afterward!

Is component wear mainly due to machining or material issues, with lubricant being secondary?

Answer: Incorrect! Component wear is related to material, machining precision, and heat treatment, but proper use of lubricant is equally important! For the same equipment, some users experience longer service life, while others face shorter lifespans; some users replace components frequently, while others rarely do—all of which are directly related to the quality of the lubricant used. In practice, we have encountered a customer who did not replace any components for three years, whereas the same component was replaced multiple times at another facility. This highlights the importance of lubricant quality.

Does the lifespan of oil seals relate to the lubricant used?

Answer: The lifespan of oil seals is directly related to the lubricant used! Some users find that oil seals fail within six months of operation, and the use of inferior lubricant is one of the main reasons. Inferior lubricant has poor anti-wear properties, leading to wear between shafts, bushings, and holes, which increases the gap between components. This results in lateral vibration of the shaft, causing the oil seal to quickly fail during the unstable operation of the shaft. Such damage is irreversible; new oil seals used on worn components will also fail rapidly. Therefore, it is crucial to use a high-quality lubricant.

How to identify the quality of lubricant?

Answer: Lubricant is akin to the lifeblood of machinery. High-performance lubricant ensures the healthy operation of machines, whereas an inferior lubricant is akin to machinery developing blood cancer, causing irreversible component wear and shortening the machine's lifespan. Therefore, using high-quality lubricant is of utmost importance.

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