The practice of analysing oils in service or analysing used oils is relatively old, having started more than a century ago in locomotive engines. Nowadays, it is one of the most important components of the so-called condition maintenance. It is a practice that consists of evaluating the condition of a machine by periodically gathering data on the main health indicators of the machine (KPIs – Key Performance Indicators), thus allowing to determine the maintenance schedules.

The Analysis


Nowadays, companies spend large amounts of money replacing machine components that wear out due to insufficient performance of their lubricating oils.

Knowing and understand how to interpret changes in the properties of the oil can increase the activity time and useful life of the assets. The performance and reliability of equipment can be optimized and problems mitigated by obtaining certain information, such as the presence of debris or particles of worn parts in the lubricating oil (a sign of erosion and/or contamination).

A detailed analysis of the characteristics of lubricating oils or other fluids makes it possible to obtain critical early warning information that may be indicative of a machine or equipment failure. By analysing and verifying a trend in the data, it will be possible to schedule maintenance before any critical failure can occur (preventive maintenance).

Routine tests will allow staying up to date and informed while allowing managing the risks to equipment and its efficiency. Therefore, being always one step ahead of problems.

Among the different parameters to be analysed in the oil, monitoring some of its physical, mechanical, and chemical properties will stand out.

The determination of the presence of metals by the ICP-MS technique (inductively coupled plasma-mass spectrometry) represents a simple, fast, accurate, and precise method to identify and quantify the presence of elements (traces), wear metals, additives, chlorine, and sulphur in oil matrices.

Another technique of extreme importance is ferrography. To perform analytical ferrography, solid residues suspended in a lubricant are separated and systematically deposited on a glass slide. The slide is examined under a microscope to distinguish particle size, concentration, composition, morphology, and surface condition from ferrous and non-ferrous wear particles. This test reveals an abnormal wear condition, identifying the wear of the component, how it was created, and what is its cause.

Particle counting is the method used to monitor solid contamination of new and in-service fluids. Each increase in the ISO code represents a doubling of the number of particles in that size range. ISO codes for particles > 4 μm > 6 μm and > 14 μm are described by ISO 4406.

The use of infrared analysis (FTIR) of used lubricating oils provides useful molecular information about changes in the lubricant and the mechanical compartment to be lubricated. This makes the technique an effective screening tool for maintenance programs. Some parameters can be identified by this technique such as the presence of soot, oxidation (degradation of the oil), presence of contamination with diesel, gasoline, or antifreeze.


Figure 1- Infrared spectrum of used oil (source:

The presence of water as a contaminant can also be determined by using Karl-Fisher equipment, which can be quantified at the level of ppm (parts per million).
In addition to the parameters described above, some physical parameters such as viscosity (at 40ºC and 100ºC) must be controlled (a measure of the resistance of a fluid to flow or shear deformation). Finally, the quantification of the Acid Value must be controlled. A high concentration of acidic compounds in a lubricant can lead to corrosion of machine parts and clogged oil filters due to the formation of varnish and sludge.

Collecting the Sample


As important as laboratory tests will be the collection of the sample and the way it is collected. For this, a correct selection of the collection bottles, vacuum pump, and tubes will be necessary.

How should the oil sample be collected? The samples must include the fluid that best represents the oil that circulates through the system during normal operations. If collections are made from multiple compartments, start with cleaning systems – usually the hydraulic system, the transmission or steering system, and finally the engine system. Note that you must use a new tube for each machine or engine. It is especially important to discard the tubing after oil sampling, as soot and oil additives can remain and contaminate other samples.

These aspects will influence the subsequent characterization of the oil since they allow guaranteeing the absence of contamination and the representativeness of the product.



In general, the results from an oil analysis allow a great number of advantages, namely, to increase the availability and productivity of the equipment, to reduce costs associated with the maintenance steps, to guarantee the occurrence of fewer interruptions and production stops. In short, it will allow a great deal of in-depth knowledge of the type of fluid used and allows the equipment to operate at an optimal level of performance and more environmentally friendly operation.