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 running, many parts are in relative motion, and the friction surfaces in contact with each other undergo high-speed relative sliding, with operating temperatures reaching 400–600°C. Under such harsh working conditions, engine oil establishes an oil film between two relatively sliding friction surfaces, separating the surfaces of the two moving parts to reduce wear. The oil flows between parts, carrying away the heat generated during operation to provide a cooling effect; it also removes wear debris from parts and contaminants from surfaces, providing a cleaning effect; and it carries away water, air, acidic substances, and harmful gases adsorbed on part surfaces, providing anti-rust and anti-corrosion effects. If deteriorated engine oil continues to be used, it can cause significant damage to mechanical components. Deteriorated oil that forms gels and deposits on the combustion chamber and piston crown creates carbon deposits, leading to abnormal engine combustion; deteriorated oil adhering to piston rings and valve stems can cause these parts to seize and stick, aggravating wear on various engine components; organic acids generated by oil oxidation and deterioration increase the oil's acid value, causing corrosion and rusting of parts (most severe on lead-bronze bearings); sludge formed from oil deterioration, resulting from the mixing of water and oil, coagulates in oil lines, not only increasing oil flow resistance but even blocking oil passages, causing the diesel engine's lubrication to fail. Therefore, engine oil quality must be monitored to achieve timely oil changes and oil changes based on quality, avoiding mechanical failures. The methods for checking engine oil quality are as follows: 1. Take two glass tubes approximately 10mm in diameter and 30mm in length. Fill one with lubricating oil that has been tested and meets quality standards, and fill the other with the oil to be tested, leaving a 5mm gap at one end, then seal both tightly with cork stoppers and wax. Invert both tubes simultaneously and measure the time for air bubbles to rise to the top. Faster bubble rise indicates a decrease in oil viscosity. If the difference between the two exceeds 1/4, it indicates that the oil quality is no longer acceptable. 2. Polish 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 regularly. If spots or pitting marks appear on the bearing shell, it indicates that the oil has undergone acidification and its quality is no longer acceptable. 3. On a clean piece of filter paper, drop one drop of new oil and one drop of the oil to be tested, then observe and compare their oil stains. If the boundary between the black center spot and the surrounding yellow oil stain of the test oil is indistinct and gradually diffuses, it indicates the oil can still be used; if the boundary between the black center spot and the surrounding yellow oil stain is clear with an obvious dividing line, and the black spot diameter is very small, less than 1/3 of the stain diameter, the oil is semi-aged; if the oil appears completely black, it indicates the oil is fully aged, its detergent-dispersant additives have been exhausted, and the oil quality is no longer acceptable. 4. If a large amount of grayish-white oil emulsion with foam is found in the oil from visual inspection, it indicates that a significant amount of water has mixed into the oil, destroying the additives and reducing viscosity, making it unable to provide lubrication. When a small amount of water enters the oil, it is harder to distinguish; observe the oil film on the dipstick—if the oil film appears yellow or brown and the marks on the dipstick are clearly visible, 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, drip oil from the oil pan onto clean cotton wadding using the dipstick, then ignite the cotton wadding away from the fuel tank. Pure, high-quality oil ignites easily, while oil containing water produces crackling or popping sounds when ignited, indicating the presence of water in the oil. Alternatively, drip oil from the oil pan 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 operates poorly or fuel atomization is inadequate, fuel or an overly rich fuel-air mixture can enter the crankcase and mix with the engine oil, diluting it. After the oil is diluted by fuel, its viscosity decreases noticeably, affecting the formation of the lubricating oil film; additionally, diesel fuel has a high pour point, causing the lubricating oil's pour point to rise and solidify at low temperatures, preventing the engine from pumping oil. When a large amount of fuel mixes into the oil, an increase in the lubricating oil level can be observed on the dipstick scale, accompanied by a diesel odor, allowing a determination that diesel has mixed into the oil. The diesel engine's oil pressure will also decrease progressively as the diesel content increases. 6. Take two glass cups (other containers may also be used), fill one with the lubricating oil to be inspected, and leave the other empty on the tabletop. Raise the cup or container filled with oil to a height of 300–400mm above the tabletop, tilt the cup rim to allow the oil to flow slowly into the empty glass cup or container on the table, and observe the oil flow process. Good-quality oil flows in a thin, uniform, and continuous stream; if the oil flow alternates between fast and slow, with large portions flowing down at times, it indicates the oil has deteriorated. 7. Take clean toilet paper, filter paper, or napkin, and drip several drops of the oil to be inspected onto it. After the oil has permeated, if there is black powder on the paper surface and a dragging sensation when touched by hand, it indicates the oil contains many impurities, showing that the oil filter's filtration is poor, but it does not necessarily mean the oil has deteriorated; if the black center spot is relatively small and light in color, with a larger surrounding yellow oil stain, and the stain boundary is indistinct and gradually diffuses, it indicates the detergent-dispersant in the oil has not been exhausted and it can still be used; if the black spot is larger, the oil appears black-brown and uniform without particles, and the boundary between the black spot and the surrounding yellow oil stain is clear with an obvious dividing line, it indicates the detergent-dispersant has failed, showing the oil has deteriorated and should be replaced promptly. Good oil has no powder, feels dry and smooth to the touch, and leaves only a yellow oil stain. 8. Rub the engine oil between the thumb and index finger repeatedly—good oil feels smooth with no friction; if a rough sensation like sand particles is felt between the fingers, it indicates the oil already contains many impurities and should be replaced with new oil promptly. Alternatively, on a clear day, use a screwdriver to lift the oil, hold it at a 45° angle to the horizontal, and observe the oil droplet against sunlight—under the light, wear debris in the oil can be clearly seen; if there is excessive debris, the oil should be replaced with new oil. 9. If the oil level in the crankcase rises and the oil becomes thinner, smell it with the nose; if a diesel or gasoline odor is detected, it indicates diesel or gasoline has seeped in. In addition to replacing the oil, the source of the diesel or gasoline should also be eliminated.