Twist the lubricating oil between the thumb and the index finger and grind repeatedly. The better lubricating oil feels lubricating, less abrasive and non-friction. There are too many impurities in it, so it can't be used anymore, it should be replaced with new lubricating oil.
2. Oil drop trace method
Take a clean white filter paper and place a few drops of oil on the filter paper. After the lubricating oil leaks, if there is black powder on the surface and there is a sense of resistance to the touch, it means that there are many impurities in the lubricating oil. The lubricating oil is powder-free, dry and smooth to the touch with a yellow mark.
3.Oil flow observation method
Take two measuring cups, one of which contains the lubricating oil to be inspected, and the other empty on the table, lift the measuring cup full of lubricating oil 30-40 cm away from the table and tilt it to let the lubricating oil slowly flow into the empty cup In the middle, observe its flow, the oil flow of good quality lubricating oil should be slender, uniform and continuous. If the oil flow is sudden and slow, and sometimes large pieces flow down, it is said that the lubricating oil has deteriorated.
On a sunny day, use a screwdriver to lift up the lubricating oil and make a 45-degree angle to the horizontal. Contrast with sunlight and observe the condition of oil droplets. Under sunlight, it can be clearly seen that there is no wear debris in the lubricating oil as good and can continue to function. If there are too many wear debris, the lubricating oil should be replaced.