From Sourcebook For Used Oil Elements

Unfiltered or poorly filtered oil eventually results in growing concentrations of wear debris. The problem is mutually compounding because the dirtier the oil, the more contaminated the oil continues to become from internal wear debris production and destruction to contaminant exclusion seals. While it is always good advice to maintain clean lubricants from a proactive maintenance standpoint (affirmative action), it is equally good advice for predictive maintenance (early wear detection). A failure to do so usually leads to the alarm signal effectively being "lost in the sauce." This concentrated debris results in a high noise threshold, and when an incipient wear signal occurs, it will "write in the noise" and be lost (signal-to-noise is less than 1:1). This is a persistent problem with splash-fed gearing, crankcase lubes, and bath-lubricated bearings.

Conversely, a clean oil not only provides a healthy and unabrasive lubricating environment but also allows the wear signal (incipient debris generation) to write above the noise level (signal-to-noise is greater than 2:1, for example). When the fluids are maintained clean and if sampling is carried out in live zones (before filters, on bearing drain lines, and at turbulent fluid zones) the early detection of wear anomalies is typically achieved. There is often a need for the routine use of portable filtration systems or retrofitted side-loop filters.

More about Sourcebook For Used Oil Elements

"How do I check to see if my aged hydraulic and/or lubricating oils can still shed water effectively?"

This is an issue of demulsibility, which is the measure of an oil's ability to release water. Of course, if you have time, your lab can run a specific test (ASTM D1401) that can be performed to measure the remaining demulsibility potential.

For a quick Pass/Fail test, measure an equal amount (1 pint each) new lubricant and water, and fill a blender. Heat to 100 degrees F (38 degrees Celsius), or whatever temperature closely resembles the operating temperature of the sump. Thoroughly mix the oil with the water. Measure the amount of time it takes to separate. Also measure how much of the mixture does not separate (the emulsion is called the 'cuff'). Now repeat the test with the aged lubricant.

If it takes more than 20 percent longer to separate, then consider having a lab run the test according to the lab procedure. If the results indicate that the demulsibility capacity is diminished, then consider how to best address the problem, particularly if the sump is prone to moisture contamination.