How to Select and Replace Lubricating Oil for Air Compressors

The lubricating oil of an air compressor is like the “blood” of the equipment. Choosing the wrong type or replacing it improperly can lead to component wear, a sharp rise in temperature, and even shorten the equipment’s service life. Mastering these two points will keep the air compressor running “healthily” at all times.

Choose the Right Lubricating Oil: Consider Equipment Type and Operating Conditions

• Reciprocating air compressors have internal friction components such as pistons and cylinders, so you should select oil specifically for reciprocating air compressors. This type of oil has strong anti-wear properties to reduce wear between the piston and cylinder wall; mineral oils like ISO VG 46 or ISO VG 68 are commonly used.
• Screw air compressors compress air through the meshing of male and female rotors, requiring oil dedicated to screw compressors. This oil has better sealing and anti-emulsification properties to prevent foam formation after oil-gas mixing. Synthetic oil is recommended as it has a longer service life.

• If the air compressor operates in a high-temperature environment (e.g., a workshop in summer), choose oil with a slightly higher viscosity (such as ISO VG 68) to prevent the oil from thinning due to high temperatures.
• In cold regions, select oil with low viscosity (such as ISO VG 32) to avoid poor fluidity at low temperatures.
• If the equipment often runs at full load, fully synthetic oil is recommended, as it has strong oxidation resistance and is less likely to produce sludge.

Replace Lubricating Oil: Incorrect Procedures Render Replacement Useless

1. Before changing the oil, must stop the air compressor and let it cool down, and only proceed after the pressure is completely relieved. Otherwise, hot oil may splash and cause injury.
2. Locate the oil drain valve at the bottom of the oil tank, open it, and drain the old oil completely without leaving any residual oil—impurities and sludge in the old oil will contaminate the new oil.
3. After draining, do not forget to remove the oil filter. Many people only change the oil but not the filter; dirt in the filter will re-enter the oil circuit, and the new oil will become dirty soon.
4. Install a new filter, then add an appropriate amount of new oil. The oil level should be between 1/2 and 2/3 of the oil level gauge scale. Too little oil will cause insufficient lubrication, while too much will increase oil consumption and temperature.
5. Do not start the machine immediately after adding oil. Let the equipment stand for 5 minutes to allow the oil to fully flow into all lubrication points. Then start the machine for an idling run of 3-5 minutes, check for oil leaks, and observe whether the oil level is normal. Add more oil if necessary.

Do Not Be Casual with Oil Change Intervals

• Generally, mineral oil is recommended to be replaced every 2,000 operating hours.
• Synthetic oil can extend the replacement interval to 4,000-6,000 operating hours.
• However, if the environment has high dust levels or high humidity, the oil should be replaced 500 hours in advance.