Is it true that the higher the viscosity of a lubricant, the better?

发布时间：2022年03月14日 14:53

First, it’s a misconception among car owners that the higher the viscosity of lubricating oil, the better. Lubricating oil viscosity is not only a basis for classifying lubricants but is also closely related to factors such as engine power, the degree of wear on moving parts, the sealing performance of piston rings, the amount of oil consumed during combustion, the ease of cold starts, and the temperature of engine components. If the viscosity of the lubricating oil is too high, several problems may arise: 1. The engine will have difficulty starting at low temperatures. When the oil viscosity is too high, the oil takes too long to circulate during cold starts. Although the oil pressure may be high, the actual flow rate of the oil is relatively low—mainly because the high viscosity impairs the oil’s pumping performance. Under these conditions, it becomes particularly easy for...

　　First, car owners are mistaken in thinking that the higher the viscosity of lubricating oil, the better.

　　The viscosity of lubricating oil is not only the basis for classifying lubricants, but also closely related to engine power output, the degree of wear on moving parts, the sealing performance of piston rings, the amount of lubricant and combustion residues, the ease of cold starts, and the temperature of engine components.

　　If the viscosity of the lubricant is too high, the following problems may arise:

　　1. The engine has difficulty starting at low temperatures. The oil viscosity is too high, causing it to lubricate the engine too slowly during cold starts. Although the oil pressure is relatively high, the actual oil flow rate is not substantial—mainly because of the high viscosity, which results in poor pumpability of the oil. Under these conditions, temporary dry friction or semi-fluid friction is most likely to occur, and this is the primary cause of engine wear. Experiments have shown that from the moment the engine starts, the torque required for rotation is already considerable; consequently, the engine speed remains low, making it difficult to start.

　　2. Significant power loss occurs. When the engine oil has high viscosity, the frictional resistance between the rubbing surfaces of the parts also increases. This not only accelerates wear on the parts but also leads to greater power loss due to friction. On the other hand, the resistance caused by the crankshaft churning the oil also rises, further increasing power losses within the engine and thereby reducing the engine’s effective power output.

　　3. Poor cooling performance. If the engine oil has high viscosity, poor fluidity, and a slow circulation rate, it will also take longer to remove heat from the friction surfaces, resulting in inferior cooling effectiveness and making the engine prone to overheating.

　　4. Poor cleaning effect. The oil is difficult to circulate, and its circulation speed is slow, resulting in fewer passes through the filter. Consequently, it cannot promptly remove impurities such as metal particles, carbon deposits, and dust that have come loose from friction surfaces.

　　Moreover, compared to low-viscosity lubricants, high-viscosity lubricants have larger residual carbon particles and a higher acid value, both of which can affect their performance.

　　So, what are the drawbacks if the lubricant’s viscosity is too low? First, the oil film is easily destroyed. With low-viscosity lubricants, it’s difficult to form an adequately thick oil film on high-friction surfaces. Such oil films have poor load-carrying capacity and tend to break down under load, failing to provide proper lubrication for the machine parts and thus increasing wear.

　　2. Poor sealing performance.

　　If the lubricating oil has low viscosity, its sealing performance will be poor, making the cylinder prone to air leaks. This not only reduces power output but also easily allows exhaust gases to enter the crankcase, diluting and contaminating the lubricating oil.

　　3. Increased lubricant consumption. If the lubricating oil has low viscosity, poor sealing performance, and high volatility, it can easily allow lubricant from the cylinder walls—especially in the high-temperature upper region of the cylinder walls—to leak into the combustion chamber, resulting in oil burning. This not only increases lubricant consumption but also leads to incomplete combustion, excessive carbon buildup in the combustion chamber, black or blue smoke coming from the exhaust, and a reduction in engine power.

　　As can be seen from this, it is undesirable for engine lubricating oil to have either too high or too low a viscosity. It is essential to select an appropriate viscosity—the “appropriate viscosity” refers to one that can form an oil film of sufficient thickness on the friction surfaces of the components, thereby ensuring the smooth operation of the machine parts.

Drinking substandard antifreeze indiscriminately is simply ruining your car!

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