The Art of Oil Analysis

The Art of Oil Analysis

Keeping on top of maintenance in a fleet is vital. The art of oil analysis can be a useful tool in drilling down into just what is happening inside an engine – or any other component requiring lubrication.

In today’s highly competitive transport market, full utilisation of every piece of equipment is critical to the success of an operation. Operators rely on their service partners to provide ways of ensuring equipment availability is achieved without compromise.

The Art of Oil Analysis

Specialists like Castrol provide lubricants to fleets backed with a comprehensive Used Oil Analysis (UOA) service to allow optimised service intervals for their particular application.

Used oil analysis has been used by equipment manufactures like Caterpillar and Komatsu for many years and has become an integral part of the mining industry’s move to proactive maintenance programs, for example. Today, the vast majority of component manufacturers in the transport and building/construction industry also recommend it and provide guidelines to assist their customers to best use the valuable information provided by oil analysis to protect their assets and reduce maintenance costs.

With transport fleets achieving up to 500,000km per year in shuttle applications, this high demand on their equipment uptime has forced operators to look for every opportunity to have a proactive and predictive maintenance strategy to avoid unexpected down time. It’s therefore no surprise that many successful fleets use and rely on used oil analysis to help them reduce maintenance costs through the early detection of issues, which allows them to schedule repairs enables them to engage the OEM for warranty coverage.

These high utilisation rates, coupled with market forces, have also seen many OEMs respond to their customers’ needs by increasing their maximum allowed service intervals. While the majority of component and truck manufacturers in the transport industry recommend their customers include used oil sampling in their scheduled maintenance regime, the task of understanding and utilising the information often falls back to the time-poor workshop manager to understand the report and take action accordingly.

With Castrol’s Labcheck ES program, the team of technical staff review the reports and provide meaningful feedback to the workshop ensuring the maximum benefit can be derived from the data.

Used oil analysis is a trending tool and when used across a fleet of vehicles and in conjunction with proper maintenance can be a powerful assistant for the workshop staff. Proper interrogation of the data can identify vehicles in the fleet that are not performing optimally, allow for optimising service intervals based on the task, and can influence future buying decisions. Collecting a long history of UOA coupled with a good service history of a piece of equipment can also increase resale value.

Different engine makes use different materials and will have their own individual set of expected results from UOA. Likewise, different emission strategies have significantly different impact on the lubricant. The technical team understand these differences and use this knowledge to guide their customers to the optimal service intervals for their needs.

With mixed fleets now commonplace, partnering with a team understanding the variation in materials and performance is critical to ensuring optimum reliability and utilisation.

The analysis of the used oils takes place in hi-tech laboratories using different combinations of physical, chemical and Spectroscopic testing. Comparison of the UOA result to that of new oil gives a great baseline for identification of changes in the engine and the lubricant itself.

The Art of Oil Analysis

Next to test methods outlined in our two lists, there are many other tests that are available for different equipment and for higher levels of analysis. For example, hydraulic systems should be analysed for cleanliness of the oil and from this an operator can monitor filter performance. Filter patch tests can be carried out and help identify the morphology of particles filtered from the sample.

Using systems like Castrol’s Labcheck ES, customers have been able to identify issues such as coolant entry into the engine oil, fuel dilution issues, poor combustion coming from incorrect timing or fuel injector issues, through to premature wear in all components including transmission and axles. The early detection of these issues allows the workshop staff to avoid costly failures reducing collateral damage and higher rebuild costs as well as avoiding expensive towing exercises.




Viscosity is a critical property of the lubricant. Manufacturers of equipment determine the viscosity of oil, which will provide adequate protection over the temperature cycle of the machine. Changes in the viscosity of the lubricant in service can indicate problems such as polymer shearing, oxidation, fuel dilution and contamination from combustion soot.


Analysis for metals includes both wear metals and the lubricant’s metal containing additives. The wear metals are used to monitor the condition of the machine, while the oil additives are monitored to ensure correct lubrication. Additives containing metals are also used in coolant manufacture and can be identified in the oil in the event of coolant ingress into the engine. Dirt ingress is also identified by an increase in aluminium, silicon and iron above the normal trend for the machine. The equipment used to measure metals in a sample identifies particles less than eight microns in size.


Oxidation occurs through reaction of the lubricant with oxygen under the influence of heat. This reaction is often assisted by wear metals generated within the vehicle. Oxidation degrades the oil and can lead to deposits and sludge formation, which ultimately lead to machine damage.

PQ Index

The so-called Particle Quantification (PQ) Index gives an indication of the magnetic material in the oil sample. Larger particles give a more significant response on the instrument. Comparing the PQ result and the result for iron from the metals testing can indicate the type of wear occurring in the equipment.

Water content

Water in the oil disrupts the lubricant film and can lead to wear in loaded contact zones. If allowed to remain in the compartment during extended periods of shut down, it can lead to corrosion and cause major damage down the line. It, too, should be monitored professionally.



Further testing is required for specific compartments, such as engines, in order to monitor the processes and contaminants specific to these.


Soot from incomplete burning of diesel in the cylinders finds its way into the lubricant by passing the piston rings. Soot leads to oil thickening and should be controlled by the dispersant properties of the lubricant. If the soot level is allowed to become elevated it can block oil filters and oil pick up screens and may result in engine damage.

Fuel Dilution

Fuel dilution lowers the viscosity of the lubricant and can also reduce the oxidation stability of the oil reducing its service life.

Base Number (BN)

Base Number (BN) is a measure of the ability of the oil additives to control acids formed during the combustion process. These additives can lead to corrosion of soft metals such as bearings.

Acid Number (AN)

Acid Number is the other half of the story from BN. As the BN falls in service, the AN can rise. The point at which the two paths cross is generally accepted as the point at which oil should be changed. AN is very important for engines running on gas fuels. Similarly it is important to monitor Hydraulic fluids for AN.