Importance of Checking and Changing Vacuum Pump oil

It’s a question we hear all the time at FJC.  “Do I REALLY need to change my vacuum pump oil?”  The answer is a resounding, “Yes—for the sake of your vacuum pump AND your system!”

Vacuum pump oil  is a special oil used to lubricate a vacuum pump.   Because a vacuum pump removes moisture, acid and other contaminants from an air conditioning system, the oil can become contaminated fairly quickly.  Once the oil is compromised in this way, the pump’s ability to remove moisture from the system is reduced and corrosion may occur.   This will cause the overall performance of the vacuum pump to diminish, resulting in poorly evacuated systems.   For these reasons, vacuum pump oil should be changed frequently to guarantee optimum performance.


  • Oil should always be changed after an initial 100 hour break-in period of pump operation.
  • Thereafter, in a shop setting, oil should be changed at least 2 times per season.
  • DIY users should change after every 20 uses, or once a year, whichever is shorter.
  • Always change oil which appears contaminated and/or is discolored.
  • Replace oil if condensation is present in the pump fluid.
  • Before and after the pump has been stored for a long period of time, it is good practice to change the fluid.
  • When vacuum pump performance has diminished, a change of oil is a good first remedy to try


It is important to frequently check the oil level of a vacuum pump.  Below is a photo of an FJC 6912 5.0 cfm Vacuum Pump which illustrates proper oil level (and clean oil!).  An over-filled vacuum pump may potentially blow excess oil from the exhaust port.  An under-filled vacuum pump will reduce lubrication, potentially causing damage to the unit and compromising performance by not allowing it a deep vacuum pull.


Only use a quality vacuum pump oil designed for rotary or piston style pumps such as  FJC Part # 2200. DO NOT USE MINERAL OIL! Regular mineral oil has not been through a distillation process to reduce its vapor pressure.