What is the method for checking car engine oil?

[OLilah]

The method for checking car engine oil is: 1. Smell test: Pull out the dipstick and smell it closely. If there is a strong sour odor, it indicates the oil has deteriorated and should be changed; 2. Finger rub test: Rub the old oil between your thumb and forefinger repeatedly. Good quality oil will feel smooth, produce little residue, and have no friction. If you feel impurities, poor viscosity, or even a rough texture, it should be changed; 3. Color test: Take a clean white filter paper and drop a few drops of old oil on it. After the oil seeps in, good quality oil will leave no powder, feel dry and smooth to the touch, and have a clear yellow infiltration zone. If it appears dark brown with impurities, it should be changed; 4. Light test: Pull out the dipstick and hold it at a 45-degree angle under light to observe the oil droplets. If you can clearly see no residue in the droplets, it is good. If there is a lot of residue, it should be changed.