Sensory and Visual Inspection
Visual Observation: Normal industrial-grade mixed oil is clear and translucent. Deteriorated oil shows a significantly darker color and turbidity; sediment or flocculent matter forms at the bottom, and abnormal layering occurs after standing for a period.
Olfactory Inspection: Fresh oil has no abnormal, irritating odor. Deteriorated oil emits a distinct rancid smell, a musty odor, or a pungent, sour stench.
Tactile Check: Rub a small amount of oil between your thumb and index finger. Normal oil feels smooth and fine without grittiness, whereas deteriorated oil feels gritty or rough, with noticeably increased friction.
Physical State Verification
Flowability Check: Normal oil flows well and has a uniform texture. Deteriorated oil exhibits an abnormal increase in viscosity; the flow becomes intermittent or drips rather than maintaining a slender, uniform, and continuous stream.
Heating Test: Heat a small amount of oil. Deteriorated oil produces copious smoke quickly, accompanied by a strong, pungent odor, and generates excessive foam that does not dissipate for a long time.
