Look at the oil color. Different varieties of oil have different colors. The light color is distillate and deep refined oil. The dark color is mostly residual oil and oil with low degree of refinement. The general gasoline is light yellow, light red, orange yellow, light diesel oil is tea yellow and the surface is blue, heavy diesel oil. It is tan, motor oil is dark brown to black, gear oil is black to black green. Smell the oil smell. Oil odors are generally classified as gasoline, diesel, sour, aromatic, and alcoholic. Adding and adding additives to the oil has a certain pungent taste, such as gasoline has a strong flavor of gasoline, light diesel oil has a diesel flavor, heavy diesel slightly diesel smell but astringent, the oil has a sour taste, gear oil has a burnt taste. This method can only distinguish the type of oil. The oil is shaken in the glass bottle to observe the “hanging bottle†condition of the oil film and the condition of the air bubbles. Generally, when the gasoline is shaken, the bubbles disappear at any time; when the light diesel oil is shaken, the bubbles are small and disappear quickly; the bubbles produced by the heavy diesel oil are The yellow color disappears quickly; the bubbles produced by the engine oil are small and large, and the disappearance is also slow. The oil “hangs the bottle†more and is yellow; the gear oil “hanging bottle†is not net for a long time, and there are few bubbles. Touch the hardness and hardness of the oil. The refined oil has a smooth and strong feeling, and the poorly refined oil has a poor smooth feel, such as astringent and astringent feeling when the gasoline is touched. The light diesel oil is relatively smooth, and the hand feels oily after being touched. The oil is slightly emulsified and slightly viscous after the water dipping. Gear oil is not easily removed.