1. Visual Inspection Method
When lubricating oil emulsifies, the oil level sight glass on the air compressor will reveal that the oil has taken on a milky-white or yellowish-white appearance, accompanied by numerous tiny bubbles; the oil level itself may also rise slightly. On some compressors equipped with a dipstick, a milky-white or yellowish-white fluid may even be seen overflowing. Furthermore, signs of deterioration may include abnormal noises from the oil pump, unstable oil pressure, or alarms triggered by the main bearing temperature monitoring system.
2. Tactile Inspection Method
As lubricating oil deteriorates, its tactile properties also change; this serves as one criterion for determining whether the oil is still in good condition. High-quality lubricating oil possesses a strong sense of lubricity; when rubbed between the fingers, it should feel smooth with no perceptible friction. If, during this rubbing process, a distinct sensation of friction is felt, it indicates a high concentration of impurities in the oil, and it should be replaced immediately.
3. Flow Analysis Method
The flow characteristics of the lubricating oil can also serve as an indicator of deterioration. Lift a container holding the oil and slowly pour it into an empty container, carefully observing the manner in which the oil flows. If the flow is uniform, slender, and continuous, it indicates that the oil quality is good. Conversely, if the volume of the flow fluctuates significantly—or if the flow rate is highly inconsistent—it suggests that the oil quality is poor. Lubricating oil typically starts with a relatively light color; however, with use, its color will gradually darken until it eventually becomes turbid. Any lubricating oil that has become excessively dark or has turned turbid should no longer be used.