How to Interpret Oil Analysis Reports

The ability to interpret oil analysis results is crucial for guiding decisions about preventive maintenance activities.This article will address the fundamentals of oil analysis and how to interpret the resulting reports.

Interpreting Viscosity Results


Viscosity is the most common test run on lubricants because it is considered a lubricant’s most important property. This test measures a lubricant’s resistance to flow at a specific temperature. If a lubricant does not have the right viscosity, it cannot perform its functions properly. A lubricant with improper viscosity can lead to overheating, accelerated wear and ultimately the failure of the component.


Measuring Metals: 
Elemental Spectroscopy


Analyzing an oil analysis report involves understanding the concentration of expected and unexpected elements in your oil. Some contaminants are picked up as the oil circulates and splashes off different machine components and surfaces. Other contaminants can enter the machine during manufacturing or routine service, as well as through faulty seals, poor breathers or open hatches. No matter how the contaminants enter the oil, they can cause significant damage.


Understanding Wear Limits


When reviewing the wear levels in your test results, look at the trend history of each machine, not just the recommendations from the original equipment manufacturer (OEM). OEMs offer good benchmarks, but it is not wise to just follow their recommendations because most machines are used differently.


For example, two identical pieces of equipment may have vastly different elemental spectroscopy results due to variations in load, duty cycle and maintenance practices. Their results might even show a variety of particle count levels. Both machines could still be considered healthy based on the trending of the analysis. 


Quantifying the Amount of Water


When free water is present in oil, it poses a serious threat to the equipment. Water is a very poor lubricant and promotes rust and corrosion of metal surfaces. Dissolved water in oil produces oxidation and reduces the oil’s load-handling ability. Water contamination can also cause the oil’s additive package to precipitate. Water in any form results in accelerated wear, increased friction and high operating temperatures.

Determining Oil Condition: Acid Number


Acid number (AN) is an indicator of oil condition. It is useful in monitoring acid buildup. Oil oxidation causes acidic byproducts to form. High acid levels can indicate excessive oil oxidation or additive depletion and can lead to corrosion of internal components.