01/05/2026 by Joel Thompson
From cutting fluid to compressor oil, lubricants are formulated to ensure equipment operates at optimal performance.
High quality brands ranging from Mobil to Morris engineer lubricants that protect and lubricate moving mechanical components. Creating a robust film on metal surfaces, they enable parts to move without connecting with each other, decreasing friction. They also keep mechanical systems cooler and capture contaminants carrying them to filters, so that machinery doesn’t get clogged with debris.
Lubricants also defend metal against corrosive forces like rust.
While modern lubricants are developed for extended use, they naturally degrade due to multiple factors including oxidation, thermal breakdown and contamination. Ultimately, the lubricant will fail and no longer be able to supply the lubricity and protection it is designed for.
Understandably, finding out that a lubricant will no longer function is information operators always want to identify before total failure occurs. Proactively replacing lubricant can avoid many unwanted outcomes like damage, equipment downtime, repairs and expensive mechanical replacements.
Here, we explore important signs of incoming lubricant failure that should never be ignored.
Increased mechanical noise and vibration
As the lubricant film begins to break down, metal-on-metal contact occurs. Moving machine parts look smooth, but have microscopic peaks called asperities that grind against each other without adequate lubrication. This increased friction causes a variety of noises ranging from squealing to knocking and increased vibration, and is a clear warning that lubricants are no longer working properly.
Sluggish operations and reduced efficiency
As lubricant starts to fail, operators often feel systems become less responsive. Increased metal-to-metal friction means equipment must work harder, typically consuming more energy and increasing operating costs.
Overheating
Fluids and oils also work as coolants, so machinery running at substantially higher temperatures is a strong indicator of the onset of lubricant failure. As oil degrades, it fails to extract heat effectively and can potentially seize equipment.
Lubricant discolouration
If a visual inspection shows that a lubricant has changed colour, it can indicate contamination and potential failure in the near future. Oil that has darkened drastically is likely heavily contaminated or suffering from oxidation. Cloudy or milky lubricant may have been contaminated with coolant or moisture.
Deposit build-up
When varnish, sludge and debris deposits form in oil, they can reduce their ability to flow, restricting their capacity to reach parts in need of lubricant. Contaminated lubricant can even block filters, so the oil bypasses them and further contaminates the system. If a sample shows the lubricant is carrying heavy deposits, it is approaching failure.
Viscosity changes
During service, lubricants are commonly subject to mechanical stress, causing them to break down (shearing) and making them thinner, impacting film strength. They can also react with oxygen and become thicker, impacting flow.
When a lubricant’s viscosity changes significantly, it requires replacement.
Acidification
Oil analysis provides detailed information on a lubricant’s condition. This includes its Total Acid Number (TAN). A rising TAN value signals potential for sludge, high wear levels and component failure.
What causes lubricant failure?
While lubricants will naturally fail over prolonged use, there are multiple factors that can lead to failure. While some are inescapable, others can be mitigated when operators make better decisions.
Contamination
Lubricants deployed in open systems are exposed to a multitude of potential contaminants. Even oils used in closed systems can encounter oxygen or moisture during fills and when leaks occur.
Lubricant contaminated by oxygen (oxidation) involves a chemical reaction resulting in base oils breaking down, causing sludge build-up, accelerated degradation and ultimately, lubricant failure.
Water contamination can cause oxidation, rust and additive depletion, reducing the strength of the lubricating film, while suspended metal shavings and dirt particles are abrasive and can increase wear on equipment parts.
Thermal breakdown
When equipment is operating at temperatures that are higher than the lubricant is designed to run at, the product starts to break down and becomes unstable and unable to create a robust oil film.
Additive depletion
Lubricant formulas typically include a base oil and specific additives. These inclusions are designed to either supress, improve characteristics of the base oil or provide entirely new properties.
Additive examples include rust and oxidation inhibitors, extreme pressure (EP) agents and detergents. Over time, in service, additives get used up, impacting the lubricant’s performance.
Incorrect lubricant type
Employing the wrong lubricant for an application can quickly cause lubricant failure. Lubricants that have the wrong viscosity or operating temperature range can result in damaged equipment and expensive maintenance.
Watch out for these early warning signs of lubricant failure and be sure to replace fluids, oils and greases that are no longer fit for service.
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