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SYSTEM OIL FLUSH: WHEN YOU HAVE TO DO IT AND WHEN YOU DON'T!

System Flushing is a bit of tricky business.

In oil circulating systems, dirt, varnish, lacquer and sludge cleaned from the systems will become partially soluble in a flushing lubricant and can be carried to filters and oil pump intake screens. These should be closely monitored to assure continued oil flow. Deposits are also likely to settle to the lowest point of the oil reservoir. Large capacity, bypass or inline filtration is recommended during cleanup for many dirty systems since the standard filters lack capacity and can quickly plug.




The Big Question is: When do we need to flush and when do we not need to flush an oil system?

This is the question that many maintenance managers, planners and lubricant specialists have trouble deciding upon. Here are the main reasons to do an oil system flush:


  1. Does the oil analysis show signs of contamination due to water?

  2. Does the oil analysis show signs of metal wear in it?

  3. Has the Total Acid Number (TAN) increased? (this is a sign that the oil is degrading)

  4. Has a filter failed or collapsed?

  5. Did the coolant leak or was there a failure?

  6. Was there an accidental mixing of the wrong lubricants in the system?

  7. Are we changing to a new oil? If so are the 2 oils compatible?

  8. Was the machine repaired or is it new?

  9. Has the machine been out of commission for a while?

Ideally anytime we find contaminants of any type in the oil analysis it is a sign that the system needs an oil flush to clean out the debris and contaminated oil. This can occur through seal leaks, water ingression, degrading of the oil additive package, coolant leak, mixing of wrong oils, selection of the wrong oil for the equipment. The advantages gained from doing an oil system flush is that you not only remove the contaminated oil but also any sludge, varnishing or debris (wear particles).


Here are some situations where we do not need to do an oil system flush:

  1. When oil analysis shows no sign of additive package degradation.

  2. When oil analysis shows no sign of metal wear or water.

  3. When the Total Acid Number (TAN) has not moved more than 10% above or below the baseline value.

  4. When there is no increase in temperature.

  5. When there is no increase in vibration.

  6. When oil analysis is good and stable and we decide to do an annual dumping of the oil and fill it with the same oil.

  7. When we are switching from one brand of oil to another and they are compatible and the last oil analysis shows no sign of issues (either with the oil itself nor any contaminants or wear particles).


The best way to avoid the need for flushing of a system is to ensure the following points are kept in check and verified:

  1. Proper oil selection for machinery

  2. Sample new oil before usage

  3. Vibration analysis

  4. Oil Analysis

  5. Proper sealing materials used

  6. Verification of temperature to keep track of fluctuations

  7. Regular cleaning of oil reservoir

  8. Clean and replace filters and separators


This preventative maintenance will help avoid the need for flushing of a system or at least lessen the amount of times it must be done; which will also decrease machine downtime.

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