12 Misunderstandings in the Use of Lubricating Oil and Grease

Diesel vehicles use gasoline vehicle engine oil

Engine oil can be classified into gasoline engine oil and diesel engine oil. Although both gasoline engines and diesel engines operate under conditions of high temperature, high pressure and high load, there are still significant differences between them. Firstly, the compression ratio of a diesel engine is more than twice that of a gasoline engine, and the main components of a diesel engine are subjected to much greater compressive impact than those of a gasoline engine. Therefore, the materials used to make some parts of the two engines are the same. For instance, the main bearing shells and connecting rod bearing shells of gasoline engines can be made of Babbitt alloy, which is relatively soft and has good corrosion resistance. However, the bearing shells of diesel engines must be made of high-performance materials such as lead bronze or lead alloy, but these materials have relatively poor corrosion resistance. For this reason, more anti-corrosion agents should be added to the diesel engine oil so that a protective film can be formed on the surface of the bearing bush during use to reduce the corrosion of the bearing bush and improve its wear resistance. Since gasoline engine oil does not have this anti-corrosion agent, if it is added to diesel engines, the bearing shells are prone to develop spots, pits, and even fall off in large pieces during use, and the engine oil will deteriorate quickly. In addition, the sulfur content in diesel is higher than that in gasoline. This harmful substance will form sulfuric acid or sulfurous acid during combustion and, along with high-temperature and high-pressure exhaust gas, enter the oil pan, accelerating the oxidation and deterioration of the engine oil. Therefore, antioxidants need to be added to diesel engine oil to make it alkaline. If acidic gas leaks in, it can play a certain neutralizing role and prevent the engine oil from oxidizing and deteriorating too quickly. Gasoline engine oil, however, does not contain such additives and is thus neutral. If it is used in diesel engines, it will deteriorate and become ineffective quickly due to the corrosion of the aforementioned acidic gases. Therefore, diesel vehicles must use diesel engine oil and cannot be replaced by gasoline engine oil.

Domestic cars use imported engine oil

Nowadays, some people believe that imported engine oil must be better than domestic one, so they use imported engine oil in domestic cars, especially new ones. This practice often leads to many problems. For instance, most imported engine oils have a relatively low viscosity, which cannot meet the viscosity requirements of domestic vehicles. Moreover, the thermal expansion systems and fit clearances of various components and materials of domestic engines are larger than those of imported vehicles. Additionally, most domestic vehicle engines do not have oil coolers. If imported engine oil is used, the oil pressure will be too low due to the oil being too thin, and may even fail to reach the specified working pressure. It fails to meet the normal lubrication requirements, accelerating the wear of the engine.

3. Blindly choosing the grade of lubricating oil

The quality of lubricating oil directly affects the service life of the engine. Especially for new vehicles, the requirements for lubricating oil are very strict. What kind of lubricating oil to choose, when to replace it, and how to replace it should all be carried out in accordance with the regulations of the manufacturer.

When choosing engine oil, both the quality grade and the viscosity grade should be taken into consideration. First, the usability level should be selected based on the compression ratio, displacement, etc. Then select the viscosity grade according to the temperature and load. High-quality engine oil can ensure good lubrication of the engine, reduce wear, extend the engine's service life, and prolong the oil change cycle. When choosing the viscosity of engine oil, except for temperature conditions, low-viscosity engine oil should be selected as much as possible under the condition of ensuring engine lubrication and sealing, so as to save fuel.

4. Mix engine lubricating oil

All kinds of lubricating oils have the same base oil except for different viscosity grades. The only difference lies in the types and quantities of added components. Therefore, lubricating oil varieties and quality grades are generally classified based on the types and quantities of added components. Lubricating oils with different types of additives should not be mixed; otherwise, the additives in the engine oil may undergo chemical reactions, damaging the inherent performance of the lubricating oil. With the continuous improvement of additives and their formulas, some general-purpose oils have been developed and produced, such as QE/CC, QF/CD and other lubricating oils, which can be used universally within the indicated grade range. Therefore, whether lubricating oils can be mixed or not should be determined by comprehensively comparing the name, type and grade of the oil in accordance with the requirements of the instruction manual. Therefore, it is necessary to rationally select the usage level and appropriate grade, and not to mix them at will.

The higher the viscosity of the lubricating oil, the better

To reduce the wear of moving parts, the lubricating oil must have sufficient viscosity to form an oil film between the moving parts at all operating temperatures. However, the viscosity of the lubricating oil must not exceed the level that affects engine starting, and it is required that the friction generated under continuous operation conditions be as small as possible. Using lubricating oil with excessive viscosity will increase the wear of parts. This is because:

(1) The viscosity of the lubricating oil is too high, and its flow is slow. Although the oil pressure is high, the flow rate of the lubricating oil is small, and the lubricating oil cannot be replenished to the friction surface in time.

(2) When the viscosity of the lubricating oil is high, the frictional resistance between the friction surfaces of the moving parts increases, affecting the power performance of the engine and the economy of fuel use.

(3) If the viscosity of the lubricating oil is high, its circulation speed will be slow, the cooling and heat dissipation effect will deteriorate, and it is easy for the engine to overheat.

(4) Due to the slow circulation speed of the lubricating oil, the number of times it passes through the filter is reduced, making it difficult to promptly clean out worn metal shavings, carbon particles, dust and other impurities from the friction surfaces.

Therefore, do not use lubricating oil with excessive viscosity, and it is even more unacceptable to think that the higher the viscosity, the better. Under the condition of ensuring lubrication, according to the temperature range during use, it is advisable to select lubricating oil with a lower viscosity first. However, for engines that are already severely worn and have relatively large clearances, it is appropriate to select lubricating oil with a slightly higher viscosity.

If the engine oil turns black, it means it has deteriorated

Engine oil operates under harsh high-temperature conditions and is prone to oxidation and deterioration, generating acidic synthetic polymer deposits that can disrupt lubrication. In addition, the exhaust gas from combustion entering the crankcase will also cause the engine oil to oxidize and deteriorate. Therefore, engine oil that has been used for a certain period of time usually turns black and deteriorates, losing its due lubricating effect. However, with the continuous improvement of lubricating oil quality, especially the promotion and application of thickened engine oil, the blackening of engine oil does not necessarily mean that it has deteriorated. This is because the cleaning dispersant added to the thickening machine oil causes the deposits on the machine parts to disperse in the oil, making the engine oil turn black. Whether it has deteriorated or not should be tested for various indicators. Oil should be changed based on quality to reduce unnecessary waste. Engine oil with protective agents such as YY 102 added will also turn black after a certain period of use. Therefore, blackening of engine oil does not necessarily mean that the oil has deteriorated.

It is best to use multi-grade lubricating oil

Multi-grade lubricating oil (also known as multi-viscosity lubricating oil) has the properties of light oil at low temperatures and those of heavy oil at high temperatures. In situations where multi-grade lubricating oil is used, one type of multi-grade oil can replace multiple single-grade oils. Although multi-grade oil can meet the fuel requirements of extremely cold and warm seasons as well as heavy-duty engines, for diesel engines that have no difficulty starting in cold weather, it is usually still recommended to use single-viscosity lubricating oil, which is beneficial for extending the service life of the engine. Therefore, do not think that using multi-viscosity lubricating oil is the best.

When adding lubricating oil, it's better to add more than less

The harm of insufficient engine lubricating oil is well known. Therefore, some car owners are afraid of burning the engine tiles due to lack of oil and often add more lubricating oil than the standard. Excessive lubricating oil has many hazards:

The crankshaft agitation causes the engine oil to form a large amount of foam and deteriorate, increasing the rotational resistance of the crankshaft. This not only raises the engine's fuel consumption but also reduces the engine's power.

(2) Due to the engine oil flowing along the cylinder wall into the combustion chamber, "oil burning" occurs, increasing the consumption of engine oil and deteriorating emissions.

(3) It accelerates the formation of carbon deposits in the combustion chamber, making the engine prone to deflagration.

Therefore, it is a misunderstanding that more engine oil is better than less. Generally, the oil level should be kept slightly below the mark on the dipstick.

Grease is applied to the cross shaft of the 90,000 universal joint

In general vehicle maintenance manuals, it is clearly stipulated that calcium-based grease should be used for the key teeth and intermediate bearings of the drive shaft telescopic sleeve, while gear oil should be used for the needle roller bearings of the cross shaft and the intermediate bearings of the rear axle transmission in three-axle drive vehicles. However, in actual work, due to the lack of filling equipment, some mechanics, for the sake of convenience, mistakenly lubricate the cross shaft needle roller bearings with calcium-based grease, resulting in the premature damage of a large number of cross shaft bearings. Because the nozzle for adding gear oil to the universal joint cross shaft is a very ordinary grease nozzle, it often gives people a misunderstanding. In fact, grease cannot be added to needle roller bearings. Because the viscosity of the grease is high, when the grease gun is used to add grease to the inner cavity of the cross shaft through the oil nozzle, the resistance of the grease entering the narrow inner oil passage is very large. At this time, the grease will push open the pressure reducing valve on the opposite side of the oil nozzle and overflow. At this point, the repairman mistakenly believes that the bearing has been filled with oil. Therefore, gear oil should be added with a gear oil pressure gun.

Apply grease when installing the cylinder gasket

Some mechanics like to apply a layer of butter on the cylinder gasket when installing it, believing that doing so can enhance the engine's sealing performance. But doing so is not only unhelpful but also harmful. The cylinder gasket is an important sealing component between the engine block and the cylinder head. It not only strictly seals the high-temperature and high-pressure gas inside the cylinder, but also seals the cooling water and engine oil that pass through the cylinder head and the cylinder block. If grease is applied to the cylinder head, some of the grease will be squeezed into the cylinder water or oil passage when the cylinder head bolts are tightened. The grease remaining on the cylinder gasket, due to the influence of high temperature, will partly flow into the cylinder and burn up, while the other part will burn into carbon deposits and accumulate on the mating surface between the cylinder block and the cylinder head, causing air leakage in the engine. Therefore, do not apply grease when installing the cylinder gasket.

Apply lubricating grease to the tire bolts or nuts

To make it easier to tighten the nuts and prevent rust, many mechanics apply lubricating grease to the tire bolts and nuts. In fact, this is a wrong approach. According to mechanical principles, after a nut is tightened, the threads have a self-locking feature, which is due to the fact that the helix Angle of the threads is less than the equivalent friction Angle between the threads. In the set bolt connection, the helix Angle is a constant value, while the equivalent friction Angle varies with the friction state between the threads. Obviously, after oiling, the equivalent friction Angle between the threads decreases, and the self-locking performance of the bolt connection deteriorates. Therefore, do not apply lubricating grease to the bolts and nuts of the tire to prevent the connection from loosening and the tire from falling off.

12. Thin the grease by adding lubricating oil

Some mechanics like to dilute grease by adding lubricating oil when using it in winter. This approach is wrong. Because the structure of lubricating grease is a colloidal structure system composed of thickener and base oil, the thickener forms a structural network, adsorbing the base oil (generally ordinary lubricating oil) in the network to form a stable structural system, ensuring that the thickener and base oil do not separate. If lubricating oil is added after the grease is formed, although it has been stirred, it cannot be evenly dispersed and contained in the network. When in use, it is very easy to separate and be lost, which is not conducive to lubrication. If low-consistency grease is needed in winter, calcium-based grease of grade 1 or 2 with a smaller number can be selected.