# 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 slide relative to each other at high speed, and the working temperature can reach 400–600°C. Under such harsh working conditions, engine oil forms an oil film between two relatively sliding friction surfaces, separating the surfaces of the two relatively moving parts, thereby reducing wear. Engine oil flows between the parts, carries away the heat generated during the operation of the parts, and plays a cooling role; at the same time, it can also carry away the wear products of the parts and the dirt on the surfaces of the parts, playing a cleaning role; and it can also 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 machine parts. 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; the organic acids generated by the oxidation of deteriorated engine oil increase the acid value of the oil, causing corrosion and rusting of machine parts (most seriously in lead bronze bearings); the sludge generated by deteriorated engine oil is the result of water and engine oil mixing, condensing in the oil pipes, which not only increases the flow resistance of the engine oil, but may even block the oil passages, making diesel engine lubrication ineffective. Therefore, the quality of engine oil must be monitored, so as to change oil in a timely manner and change oil according to quality, avoiding the occurrence of 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; if the bubbles rise quickly, it indicates that the viscosity of the engine oil has decreased. If the difference between the two exceeds 1/4, it indicates that the quality of the engine oil is no longer acceptable. 2. Grind a bearing shell into a long strip, fix it at the oil level mark at the lower end of the engine 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 no longer acceptable. 3. On clean filter paper, drop one drop of new oil and one drop of test oil, and observe and compare their oil traces. If the boundary between the black center point of the test oil and the yellow oil trace around it is not very obvious and spreads gradually, it indicates that it can still continue to be used; if the boundary between the black center point and the surrounding yellow oil trace is clear and there is an obvious dividing line, and the diameter of the black point is very small, less than 1/3 of the diameter of the spot, the engine oil is semi-aged; if the engine oil appears completely black, it indicates that the engine oil has completely aged, the detergent-dispersant additives in it have been completely consumed, and the engine oil quality is no longer acceptable. 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 mixed into the engine oil, causing the additives to be destroyed and the viscosity to decrease, so that it cannot play a lubricating role. After a small amount of water enters the engine oil, it is relatively difficult to identify: observe the oil film on the dipstick. If the oil film is yellow or brown and the dipstick mark is 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 and water droplets are found on the oil filler cap, it indicates that the oil contains water. The oil in the oil pan can be dropped with the dipstick onto clean cotton thread, away from the fuel tank, and the cotton thread can be ignited: pure high-quality engine oil ignites easily, while engine oil containing water makes a sizzling and crackling sound after ignition, indicating that the engine oil contains water. The oil in the oil pan can also be dropped onto white paper for identification: lubricating oil containing 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 enter 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 has a high freezing point, which causes the pour point of the lubricating oil to rise and solidify at low temperatures, making it impossible for the engine to pump engine oil. When a large amount of fuel is mixed 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 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 increases. 6. Take two glass cups (other containers may also be used), one containing the lubricating oil to be checked, and place the other empty on the tabletop; raise the measuring cup or container full of engine oil to 300–400 mm above the tabletop, tilt the mouth of the cup, and let the engine oil slowly flow into the empty glass cup or container on the tabletop, and observe the flow process of the engine oil. Good-quality engine oil has a thin, long, and uniform oil stream that is continuous; if the oil stream is sometimes fast and sometimes slow, and sometimes large masses of liquid flow down, it indicates that the engine oil has 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 paper surface 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 deteriorated; if the black center point in the engine oil is relatively small and light in color, the yellow moist trace around it is relatively large, and the oil trace boundary is not very 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 point is relatively large, and the oil is dark brown, uniform, and free of particles, and the boundary between the black point and the surrounding yellow oil trace is clear with an obvious dividing line, it indicates that the detergent-dispersant additives in it have failed, showing that the engine oil has deteriorated and should be replaced in a timely manner. Good engine oil has no powder, feels dry and smooth when touched by hand, and has only yellow oil traces. 8. Rub the engine oil repeatedly between the thumb and index finger. Good engine oil feels smooth and has no friction; if it feels as if there are rough particles such as sand between the fingers, it indicates that there are already many impurities in the engine oil and new engine oil should be replaced in a timely manner. Or, on a clear day, 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, it can be smelled with the 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 gasoline should also be eliminated.