Oil Analysis Reports: How to Improve Your Diagnostic Success

Wes Cash, Noria Corporation

Equipment seldom fails without the oil knowing first. How in tune are you with your oil analysis reports to catch incipient failures? Learn how the pros diagnose lubricant and machine failure from the data you are already collecting. Hone your skills in reading oil analysis reports and catch failures before they become catastrophic.


To begin dialing in the accuracy of your oil analysis report reading, you must first ensure that you are subjecting the oil to the proper tests. This is known as the test slate. These tests must be developed specifically for each machine or failure mode you are attempting to diagnose. To begin, you must understand which questions you want answered from your lubricant.

Often, these questions include is my oil still good, is my machine healthy, is there anything that could cause a problem, or am I using the right lubricant. These questions and many others can be answered with a well-designed test slate.

A good oil analysis test slate relies on getting key information from three aspects of the lubricant and machine. These are generally referred to as the “iron triangle” of oil analysis. It includes fluid properties, contamination and wear debris. With information from each of these categories, you will be better equipped to make maintenance decisions and be confident that you are addressing the root cause of the problem.

Within the different categories, there are many tests that must be grouped together, as there is not a single test that will provide all the information. You must look to identify trends in the test results to determine if something is alarming. Therefore, you will be heavily dependent on a reference or baseline sample to know where the oil begins prior to service. You can then compare results over time to this baseline.

Testing Categories

Fluid property tests are perhaps the most common. They reveal the health of the lubricant. The most important property to analyze is viscosity. Viscosity must remain constant. Any variability is an indicator of an impending problem with the oil. Other tests that can offer insight into the health of the oil are acid number, base number, additive levels and Fourier transform infrared (FTIR) spectroscopy.

Contamination is a leading indicator of both lubricant and machine failure. It can take many forms, but the most common are solid contaminants and moisture. Solid contaminants often are quantified using particle counting and listed under the ISO 4406:99 code.

This provides insight into how many contaminants are in the fluid. Moisture levels are reported in parts per million. Contamination typically will have upper limits that you should try to stay below and targets that you attempt to achieve. You can also test for other forms of contamination based on the machine type, such as fuel, glycol, cleaning agents and process chemicals.

Wear debris offers valuable information about the equipment’s health. As a machine begins to break down, a certain amount of wear debris is generated. The beginning stages of wear are classified by smaller pieces of metal. As the wear pattern becomes more catastrophic, the debris becomes larger.

Depending on the testing that is performed, you may have useful data on small or large debris. It is difficult to identify a single test that provides good information on both without sacrificing something in the process.

The same is true for the machine’s metallurgy. If the debris is mostly ferrous, better testing is available that can offer information about this debris. For non-ferrous material, the testing can be more challenging. Knowing the metals that make up the machine will be critical in selecting the correct test as well as knowing what to look for in the reports.


Trending test results over time will show how the lubricant and machine are aging. Identifying trends and then determining the rates of change will help you make better maintenance decisions. The trends should be normalized based on run hours and make-up fluid, as these factors will impact the data.

When reading oil analysis reports, start with the general overview. Ensure the lubricant and machine names are correct and that there was not a mix-up at the lab. It is helpful to know the run time on the machine and the oil to help with trending, but you can also compare current levels against the baseline sample.

Typically, a flag in the corner of the report will indicate a caution or critical state. Simply using this as an indication is not effective, as there may be trends that tell you something is about to happen even if the results appear to be normal. It is best to review all the reports regardless of whether they are deemed “OK” or not.

Interpreting the results will take practice and time to master. When performing this task, dedicate enough time to review the reports in detail. Even if the numbers look good, dive deeper, as you can often discover issues that may not yet be catastrophic but are trending in that direction.

Read more on oil analysis report best practices:

Statistical Techniques to Simplify Oil Analysis Data

How to Select the Right Oil Analysis Tests

How to Justify an Oil Analysis Program


This article was previously published in the 2018 Machinery Lubrication Conference Proceedings.

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About the Author

Wes Cash is the director of technical services for Noria Corporation. He serves as a senior technical consultant for Lubrication Program Development projects and as a senior instructor for ...