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Maintenance and Inspection of Diesel Engine Lubricating Oil

Mar 20, 2024 | Technical Literature | 0 comments

As far as engine oil is concerned, it needs to be replaced in a timely manner during the operation of the diesel generator, and the selection of its replacement cycle must be scientific and reasonable. The implementation of this replacement measure is mainly determined by the quality indicators of the engine oil. At this stage, we have basically got rid of the use of timely oil change measures in the past and popularized the more accurate basis of oil change according to quality. Since many users today do not have complete oil testing equipment, this has hindered the rapid and accurate testing of engine oil quality. At this time, we can generally use on-site rapid detection methods to measure the engine oil in use. That is to say, based on the appearance, smell, and regular inspection of impurities by front-line operators and the oil stain test, viscosity change test, and sedimentation test by on-site technicians, we can promptly and accurately grasp the diesel engines of all mining equipment. The degree of contamination of the engine oil in use.

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1.Lubrication system maintenance and management

The function of the diesel lubrication system is to ensure the supply of oil required for the lubrication and cooling of the moving parts of the diesel engine power plant. The oil is stored in the diesel engine oil pan. When the diesel engine is in normal operation, the oil pan oil is pumped by the oil pump and sent to the lubrication parts by the oil cooler. After lubrication, the oil pan flows back to form an independent lubrication system.

(1) Correctly select lubricating oil

Reasonably select lubricating oil according to requirements, and deliver lubricating oil of qualified quality to various parts that need lubrication to ensure their normal operation.

(2) Ensure the working pressure of the lubricating oil

The working pressure of the lubricating oil should be adjusted according to the instructions. Generally it should be kept at 0.15Mpa~0.4Mpa. The pressure of the lubricating oil should be higher than the cooling water pressure to prevent coolant from leaking into the lubricating oil when cooling leaks. The pressure of the lubricating oil can be adjusted by the bypass valve of the lubricating oil pump.

When the pressure of the lubricating oil is too high, the lubricating oil will splash in all directions, and the joint surface will easily leak oil. It will be easily oxidized and deteriorated by heat in the crankcase, which will also increase the consumption of lubricating oil. When the lubricating oil pressure is too low, the wear of the machine parts will increase due to insufficient oil supply to the bearings. In severe cases, major machine damage accidents and safety accidents may occur.

(3) Ensure the working temperature of the lubricating oil

If the temperature of the lubricating oil is too low, the viscosity increases, the friction loss increases, and the power consumption of the lubricating oil pump increases; if the temperature of the lubricating oil is too high, the viscosity decreases, the lubrication performance deteriorates, the wear of parts increases, and the lubricating oil is prone to oxidation and deterioration. Generally, the lubricating oil inlet temperature should be maintained at 40°C ~ 55°C; the maximum temperature is not allowed to exceed 65°C; the temperature difference between the inlet and outlet is generally 10°C ~ 15°C. The temperature of the lubricating oil can generally be adjusted through the bypass valve of the oil cooler.

(4) Ensure normal working oil level

Check the oil pan oil level frequently to ensure normal oil level. If the oil level is too low, the temperature of the lubricating oil will rise, which will easily cause the lubricating oil to volatilize in the crankcase. In addition, if the lubricating oil circulates too many times per unit time, the impurities in the oil cannot be fully precipitated in the circulating oil tank, which will accelerate the oxidation and deterioration of the lubricating oil, and in severe cases, there will be a risk of oil outage. If the oil level is too high, there may be a risk of oil spillage. If the oil level suddenly drops during operation, it may be caused by leakage in the oil pan or piping system; if the oil level suddenly rises, it may be caused by water leaking into the cooling system.

(5) Check the oil filter regularly

During routine inspections, the pressure difference between the inlet and outlet of the oil filter should be checked frequently to prevent it from affecting the normal operation of the diesel engine. When cleaning the filter, you can soak it in detergent or diesel, use a soft brush to remove dirt, blow it with compressed air, etc. Do not damage its parts. The automatic backwash filter should be disassembled and assembled according to the instructions and cleaned with special tools.

2.Lubricating oil inspection

In order to grasp the deterioration patterns of lubricating oil in a timely manner so that effective measures can be taken accordingly, crankcase oil needs to be inspected regularly. There are usually several methods:

(1) empirical method

According to the operator’s experience, through visual inspection of the crankcase oil, such as touching (viscosity), smelling (odor), looking (color), and checking the deposited sludge in the lubricating oil separator, observing the splash on the crankcase wall The color of the lubricating oil on the piston, the carbon deposits in the piston cooling chamber, etc. can roughly qualitatively determine the deterioration of the lubricating oil.

(2) Oil stain test method

In this method, the lubricating oil to be tested is dropped on a special test paper. After the oil droplets are dried, the lubricating oil can be roughly judged based on its diffusion and color changes compared with the provided standard image (or the diffusion and color of new oil). of deterioration. If the black spot in the center of the oil stain is smaller and lighter in color, and the surrounding yellow oil stains are larger, it means that the lubricant can still be used; if the black spot is larger and the dark brown is uniform and without particles, it means that the lubricant has deteriorated.

(3) Assay method

Assay methods allow quantitative analysis of lubricating oils. According to the usage requirements, it can be divided into two types: simple testing on board and laboratory testing. Simple testing can be performed on-site at the generator set site, and the testing equipment (Onboard test kit) used is provided by the oil supplier. Testing should be carried out according to its prescribed methods, and the values of performance indicators such as viscosity, moisture, salt, total alkali value, strong acid value, insoluble matter, etc. can be obtained. In this way, the deterioration of lubricating oil can be judged more accurately and in a timely manner. For laboratory testing, the operator should take out the oil sample from the generator set and send it to a land laboratory (usually an oil supplier) for quantitative laboratory analysis. The operator can conduct a comprehensive analysis and decide on treatment measures based on the laboratory analysis sheet. Usually, the analysis conclusion of the lubricating oil and the corresponding treatment measures are already on the laboratory analysis sheet.

3.Lubricating oil index

At present, there is no unified standard for the allowable limits of various indicators of lubricants, which are generally set by manufacturers. The allowed change limits of each indicator are roughly:

(1) Viscosity

The viscosity of the lubricating oil in use may decrease (mixed with diesel) or increase (mixed with heavy oil or oxidize itself). It is generally believed that the viscosity of lubricating oil should not change by more than 25% or 20% of the initial value.

(2) Total acid value

The oxidation of the lubricating oil itself and the leakage of acidic products in the combustion products both increase the total acid value. The rate of change of the total acid number is more important than its absolute value because it can indicate whether the oil has a tendency to deteriorate rapidly and develop deposits and blacken. The total acid value has a slow change period, and the total acid value may increase rapidly in the later stage of the slow change. Generally, if the total acid value changes rapidly, the value is not allowed to exceed 25 mg KOH/g. If the total acid number changes slowly, up to 4 mg KOH/g is allowed. However, if a strong acid value occurs, the total acid value is only allowed to reach 25 mg KOH/g.

(3) Strong acid value

The leakage of acidic substances in combustion products will cause an increase in the strong acid value. Lubricants in normal use are not allowed to have a strong acid value. If a strong acid value occurs, sufficient attention should be paid, the cause should be identified immediately, and effective measures should be taken (such as washing with water, etc.).

(4) Total alkali value

The total alkali value of the lubricant decreases in use as the alkaline additives are consumed. A total alkali value of zero or a strong acid value is not allowed.

(5) Moisture

Moisture in the lubricating oil is caused by leaks in the cooling system. When the moisture exceeds 0.5%, the cause should be identified and treated with a lubricating oil separator.

(6) Salinity

Cooling water leakage into the lubricating oil will appear salt, salt has a corrosive effect. The cause should be identified and treatment measures taken. Water washing method can eliminate salt, but should consider whether the additives in the lubricant are soluble in water.

(7) Deposition of insoluble matter

Insoluble deposits in lubricating oil include combustion products, wear debris, rust and oxides. These contaminants can increase lubricant viscosity and create sludge. For crosshead diesel engines that use pure mineral lubricating oil and have continuous separation and purification equipment, the deposited insoluble matter generally does not exceed 0.5%. If it exceeds 1%, it means that the lubricating oil is seriously polluted. For cylindrical piston diesel engines using additive lubricants, the deposited insoluble matter in the lubricating oil is allowed to be up to 3%, because this kind of lubricating oil has the ability to suspend and carry solid particles.

The oxides in the sedimentation insoluble matter are soluble in benzene but not in n-heptane, so n-heptane and benzene are used to measure the amount of sedimentation insoluble matter respectively, and the difference is the weight of the oxide. Generally speaking, sediments mostly refer to n-heptane insoluble matter.

(8) Flash point

Fuel leakage will lower the flash point of the lubricant. Generally, when the flash point is lowered by 40°C or more, the cause should be identified.


When analyzing the above laboratory indicators, changes in each indicator should be comprehensively analyzed, and changes in a certain indicator should not be emphasized. And from the above introduction, we can know that the detection of diesel engine oil can, to a large extent, prevent the phenomenon of continued use due to the deterioration of the performance of the oil in use and the oil change deadline, and further prevent the occurrence of engine wear. In other words, strengthening the detection of in-use engine oil and improving the detection methods of diesel engine oil can comprehensively and timely grasp the qualitative change process and pollution degree of in-use engine oil. This will greatly help ensure good lubrication of diesel engines and effectively extend Diesel engine service life.

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