I recently read an interesting webpage dedicated to the claim that oil "lasts forever." Woven between the words was the commercial message that used oils can be reclaimed and additives returned. Undeniably, there are many degrees of oil degradation. In the mildest sense, some used oils can, in fact, be restored to "like new" condition through the cleansing of contamination, including water and acid products. In certain instances, additive reconstruction is prescribed and remarkably effective.
But unlike a fine wine, oil does not improve over time or even remain stable. In typical service, oil faces many of its archenemies, and with each encounter, something is sacrificed. Water, heat, metal debris, entrained air, pressure, and mechanical action are the forcing functions that lead to stress, distress, and eventually dysfunction of the oil.
In its original domicile deep below the earth, oil endures the ravages of millions of years. Yet despite the heat and exposure, one contaminant is generally missing from its environment, preventing degradation. This, of course, is oxygen. Without air, lubricating oil would not need many of the additives so common in modern formulations. Anti-oxidants, rust inhibitors, corrosion inhibitors, and over-based additives all battle the consequences of oxidation–some proactively, others reactively.
From a maintenance perspective, what can be done to postpone the inevitable and extend an oil's service life? One practical approach would be to remove the forcing functions, including the contaminants that poison an oil and sacrifice critical additives. Another approach, directed by the "repetitive why," is to deal with the contaminants’ precursors. For instance, why do in-service lubricants, once clean, become contaminated? Why does stored oil, once clean, become laden with dirt and water? Why does new oil, once clean at the refinery's spigot, require filtration before use?
It usually doesn't take much digging to unearth the answers to these basic questions. In fact, there are many users of lubricants who are quite wise to the precursors of machine wear and oil degradation. They routinely expect, indeed demand, affirmative action to insure quality and purity of lubricants at each point in the chain of supply and usage. For these users we see oil products being delivered to pre-defined quality standards and then verified. Storage and handling is not haphazard but an engineered and documented process. And the transient conditions of in-service lubricants are controlled proactively and monitored regularly.
While it is a bit too much to expect lubricants to "last forever," there is every reason to expect them to perform better and last longer–much longer.