# Methods for Identifying the Quality of Tractor Engine Oil

If the engine is the heart of a tractor, then engine oil is the blood of the engine. When the engine is working, many parts are in relative motion, and the friction surfaces in contact with each other undergo high-speed relative sliding, with working temperatures reaching 400–600°C. Under such harsh operating conditions, engine oil forms an oil film between two relatively sliding friction surfaces, separating the surfaces of the two relatively moving parts and thereby reducing wear. Engine oil flows between the parts, carrying away the heat generated during operation and playing a cooling role; it can also carry away wear products from the parts and dirt on the surfaces, playing a cleaning role; and it can carry away water, air, acidic substances, and harmful gases adsorbed on the surfaces of the parts, playing an anti-rust and anti-corrosion role. If deteriorated engine oil continues to be used, it will cause great damage to the components. Gum-like deposits from deteriorated engine oil settle in the combustion chamber and on the top of the piston, forming carbon deposits and causing abnormal combustion in the engine; deteriorated engine oil adhering to the piston rings and valve stems will cause these parts to seize and stick, aggravating wear of all engine components; organic acids generated by the oxidation of deteriorated engine oil increase the acid value of the oil, causing corrosion and rusting of components (most seriously in lead bronze bearings); the sludge generated by deteriorated engine oil is the result of water mixing with engine oil, condensing in the oil pipes, which not only increases the resistance to oil flow but may even block the oil passages, causing the diesel engine to lose lubrication. Therefore, the quality of engine oil must be monitored, and timely oil changes and quality-based oil changes must be carried out to avoid mechanical accidents. The methods for checking engine oil quality are as follows: 1. Use two glass tubes with a diameter of about 10 mm and a length of about 30 mm. Fill one with lubricating oil that has been tested and meets the quality standard, and fill the other with the test oil, leaving a 5 mm gap at one end, then seal the openings tightly with a cork and wax. Invert both tubes at the same time and measure the time for the bubbles in the tubes to rise to the top. A faster rise of the bubbles indicates that the viscosity of the engine oil has decreased. If the difference between the two exceeds 1/4, it indicates that the engine oil quality is already unqualified. 2. Grind a bearing shell into a long strip, fix it at the oil level mark on the lower end of the oil dipstick, and observe it frequently. If there are spots or peeling pits on the bearing shell, it indicates that the engine oil has become acidic and its quality is already unqualified. 3. On clean filter paper, drop one drop of new oil and one drop of test oil, and observe and compare their oil stains. If the boundary between the black center of the test oil and the surrounding yellow oil stain is not obvious and spreads gradually, it indicates that it can still continue to be used; if the boundary between the black center and the surrounding yellow oil stain is clear, with an obvious dividing line, and the diameter of the black center is very small, less than 1/3 of the diameter of the stain, the engine oil is semi-aged; if the engine oil is completely black, it indicates that the engine oil has completely aged, the detergent-dispersant additives in it have been consumed, and the engine oil quality is already unqualified. 4. If a large amount of grayish-white oil emulsion is found in the engine oil from its appearance, accompanied by foam, it indicates that a large amount of water has already mixed into the engine oil, causing the additives to be destroyed and the viscosity to decrease, so that it cannot perform a lubricating function. After a small amount of water enters the engine oil, it is relatively difficult to identify. You can observe the oil film on the dipstick. If the oil film is yellow or brown and the dipstick marks are clearly visible, it indicates that the oil quality is good. When the engine is hot, pull out the dipstick. If water bubbles are found in the oil, or water droplets are found on the oil filler cap, use the dipstick to drop the oil from the oil pan onto clean cotton thread, and after moving away from the fuel tank, ignite the cotton thread. Pure high-quality engine oil ignites easily, while engine oil with water makes sizzling and popping sounds after ignition, indicating that the engine oil contains water. You can also drop the oil from the oil pan onto white paper for identification. Lubricating oil with water spreads quickly on the paper, while pure lubricating oil does not spread. 5. When the fuel supply system is not working well and fuel atomization is poor, fuel or a large amount of overly rich fuel-air mixture will blow by into the crankcase and mix with the engine oil, diluting the engine oil. After the engine oil is diluted by fuel, its viscosity will decrease significantly, affecting the formation of the lubricating oil film; in addition, diesel fuel has a high freezing point, which causes the pour point of the lubricating oil to rise, causing it to solidify at low temperatures, and the engine cannot pump the engine oil. When a large amount of fuel mixes into the engine oil, an increase in the lubricating oil level can be observed from the dipstick scale, accompanied by a diesel smell, and it can be judged that diesel fuel has mixed into the engine oil. The engine oil pressure of a diesel engine will also become lower and lower as the amount of diesel fuel increases. 6. Take two glass cups (other containers are also acceptable). Fill one with the lubricating oil to be checked, and place the other empty one on the table. Raise the measuring cup or container filled with engine oil to 300–400 mm above the tabletop, tilt the mouth of the cup, and let the engine oil flow slowly into the empty glass cup or container on the table, observing the flow process of the engine oil. Good-quality engine oil has a thin, long, uniform, and continuous oil stream; if the oil stream is sometimes fast and sometimes slow, with large blobs of liquid flowing down at times, it indicates that the engine oil has already deteriorated. 7. Take clean toilet paper, filter paper, or napkins, and drop several drops of the engine oil to be checked onto them. After the engine oil penetrates, if there is black powder on the surface of the paper and it feels obstructive when touched by hand, it indicates that there are many impurities in the engine oil, showing that the filtering effect of the engine oil filter is poor, but it does not mean that the engine oil has already deteriorated; if the black center in the middle of the engine oil is relatively small and light in color, the surrounding yellow oil stain is relatively large, the boundary of the oil stain is not obvious and spreads gradually, it indicates that the detergent-dispersant additives in the engine oil have not been exhausted and it can still continue to be used; if the black center is relatively large, and the oil is dark brown, uniform, and without particles, and the boundary between the black center and the surrounding yellow oil stain is clear with an obvious dividing line, it indicates that the detergent-dispersant additives have already failed, showing that the engine oil has deteriorated and should be replaced in time. Good engine oil has no powder, feels dry and smooth to the touch, and has only yellow oil stains. 8. Rub the engine oil between the thumb and index finger repeatedly. Good engine oil feels smooth and non-abrasive; if a rough feeling like sand particles is felt between the fingers, it indicates that there are already many impurities in the engine oil and new engine oil should be replaced in time. On a clear day, you can also use a screwdriver to lift up the engine oil at a 45° angle to the horizontal plane and observe the oil droplets against the sunlight. Under illumination, wear debris in the engine oil can be clearly seen. If there is too much wear debris, new engine oil should be replaced. 9. If it is found that the oil level in the crankcase has risen and the engine oil has become thinner, smell it with your nose. If a diesel or gasoline smell is detected, it indicates that diesel or gasoline has seeped in. In addition to replacing the engine oil, the source of the diesel or gasoline should also be eliminated.