Oil Analysis: The Tests

Oil analysis testing is one of the most effective ways to monitor machinery condition, detect contamination early and extend equipment life. At Clean Oil Services, we provide comprehensive oil analysis testing services that help businesses identify wear, contamination and lubricant degradation before major failures occur. Regular oil testing improves reliability, reduces downtime and supports pro-active maintenance planning across engines, hydraulic systems, gearboxes and industrial equipment.

Water Contamination Testing

Water is one of the most destructive contaminants found in lubrication systems. It often enters machinery through condensation, leaking coolers, wash-downs or environmental exposure.

Even small amounts of water contamination can:

• Degrade lubricant performance
• Promote acid formation
• Reduce film strength
• Cause corrosion and surface damage

It is one of the most common causes of failure. Under heavy load conditions, water can rapidly vaporise with an expansion factor of up to 2,000 times, damaging metal surfaces, eventually leading to costly component failure..

In engine oils, water contamination is especially dangerous because sulphur compounds combine with water and oxygen to form corrosive acids that attack bearings and internal components. Because engine oil operates at elevated temperatures that naturally vaporise incidental condensation, any detectable water in the oil generally points to an internal source of leakage.

A positive water test should never be ignored.

Immediate corrective action should include:

• Identifying the contamination source
• Rectifying leaks or ingress points
• Replacing contaminated oil if required
• Monitoring for ongoing contamination issues

Diesel Dilution Testing

Diesel dilution is a major cause of engine oil degradation and premature engine wear. When diesel fuel enters engine oil, viscosity drops and lubricant film strength weakens. Excessive dilution can significantly reduce lubrication protection and increase wear rates.

Common causes of diesel dilution include:

• Excessive idling
• Inefficient combustion
• Over-fuelling
• Injector problems
• Internal engine faults

High diesel dilution levels can also reduce oil flash points, creating dangerous operating conditions and increasing the risk of sludge formation. Any reading over 1% should be acted on as this will cause a significant viscosity drop of approximately 20%.

Conversely, caution is required when assessing diesel levels. Unburned fuel can promote heavy sludge formation, raising the oil’s viscosity until it becomes unpumpable within the engine, resulting in oil starvation and catastrophic damage.

Any positive diesel‑dilution result should be examined closely. Elevated soot levels and black smoke indicate both severe engine wear and significant fuel loss through the exhaust. Because soot particles are roughly four times more abrasive than dust, they contribute heavily to wear, and their size increases as combustion efficiency declines.

Never wash or flush lubrication systems with diesel fuel, as residual diesel can dilute fresh oil and damage lubricant integrity.

Total Base Number (TBN) Testing

Total Base Number (TBN) measures the oil’s alkaline reserve used to neutralise acids formed during combustion.

As engines operate, combustion by-products combine with oxygen and moisture to form harmful acids. The oil’s additive package neutralises these acids, but over time the reserve becomes depleted. This base reserve is expressed as the Total Base Number, which quantifies the oil’s alkalinity. It is calculated by measuring how many milligrams of potassium hydroxide are needed to neutralise the base reserve in one gram of oil (mg KOH/g).

TBN testing helps determine:

• Remaining oil life
• Combustion efficiency
• Acid neutralisation capacity
• Appropriate oil drain intervals

Extended drain interval oils often require higher starting TBN levels to maintain adequate protection over longer service periods. Standard engine oils generally start with a TBN of about 6 to 9, while oils used for extended drain intervals may be as high as TBN 15. A TBN lower than 3 indicates the oil is due for replacement.

TBN can also be used to assess combustion efficiency, particularly when it declines rapidly. Poor combustion permits unburned diesel to pass into the oil as blow‑by, generating acids that quickly deplete the TBN reserve. This is frequently reflected in elevated exhaust emissions and, in extreme situations, the formation of large, wet soot particles that contribute heavily to engine wear.

Have your TBN checked periodically in your engine to monitor combustion efficiency.

Remember when practicing extended drain intervals in engines, always have your TBN checked. Along with viscosity, it serves as a key indicator of when the oil should be changed.

Total Acid Number (TAN) Testing

Total Acid Number (TAN) testing measures acid build-up within lubricants used in non-combustion systems.

Systems such as:

• Hydraulic systems
• Gearboxes
• Turbines
• Industrial lubrication systems

As lubricants age and additive packages deplete, acids can form through oxidation, moisture contamination and chemical breakdown. Excessive acid formation can damage metal surfaces and reduce lubricant performance.

In gear and hydraulic systems, the sulphur and chlorine compounds present in the oil can react with water and oxygen, leading to the formation of hydrochloric and sulphuric acids. Even at low concentrations, these acids can damage metal surfaces if not controlled. Consequently, routine acid‑level monitoring is essential—especially in long‑drain applications such as turbines, hydraulic systems, and gearboxes.

Any rapid rise in TAN should never be left unchecked. A TAN of 0.5 mgKOH/g should be watched. However this level will depend on the system application and limits set by OEMs.

Monitoring TAN levels helps identify:

• Lubricant oxidation
• Oil degradation
• Moisture-related contamination
• Potential corrosion risks

Sudden increases in TAN levels in non-combustion compartments should always be investigated and addressed promptly.

Microscopic Analysis

Microscopic Analysis is one of the most valuable tools in used oil condition monitoring because it allows technicians to visually examine contamination and wear particles inside the oil sample.

This analysis helps identify:

• Wear particle concentration
• Wear particle type and shape
• Contamination sources
• Lubricant condition
• Oil performance issues

Microscopic analysis provides detailed insight into machinery condition and allows accurate wear trending over time.

The limitation of an optical microscope is that, aside from colour, it cannot determine the composition of particles without resorting to a costly scanning electron microscope. For this reason, we pair optical microscopy with ICP spectrometry, which provides the elemental information needed to identify particle composition.

Our microscopic examination involves counting the particles and grouping them into three size ranges:

• 0–10 µm
• 10–20 µm
• greater than 20 µm

These counts and size distributions form the foundation of our wear‑trend analysis. We then identify the particle types and classify them accordingly, which provides valuable insight into the oil’s performance.

Common Wear Particle Types

Rubbing Wear

Normal wear particles generated during standard component operation. They are caused by the asperities being torn off the surface under load. Excessive levels may indicate accelerated wear conditions.

Cutting Wear

Generated when surfaces contact directly or contaminants gouge internal components. Cutting particles are easily identifiable by their shape similar to a scoop of ice cream, lathe swarf or needle like slithers. Often linked to insufficient lubrication or incorrect viscosity.

Laminar Wear

Thin surfaced particles that may indicate rolling element fatigue or surface failure.

Fatigue Wear

Caused by repeated loading and surface fatigue cracking, resulting in a particle being generated. The result is seen as common pitting of the surface. and is commonly seen in bearings and heavily loaded components.

Spherical Particles

Form when two components enter a boundary‑lubrication condition and molten metal is generated under extreme load. As this molten metal is carried away in the oil, it cools and solidifies into spheres due to uniform pressure in all directions. Their presence is a serious warning sign and typically indicates oil‑film failure. In some cases, they may also result from electrical activity such as eddy currents and are commonly seen in large motor bearings or in hotter tropical environments.

Dark Oxides and Sludge

Commonly known as sludging, High levels of dark oxides usually cause an increase in viscosity and indicate lubricant oxidation, degrades oil condition and exhausted additive performance. is spent. They also indicate severe operating conditions in an engine.

Particle Contamination

Dust, dirt and environmental contamination can be visually identified and monitored for operational cleanliness. Microscopic analysis also allows visual assessment of soot concentration, contamination severity and overall lubricant condition.

The microscope also allows us to visually assess the condition of the oil and determine whether it is suitable for continued use, requires cleaning, or should be discarded.

IF WE REDUCE CONTAMINATION AND WEAR, MACHINE AVAILABILITY INCREASES, AND BOTH COMPONENT LIFE AND OIL LIFE ARE EXTENDED.

Spectrographic Analysis

Spectrographic Analysis uses high-temperature plasma technology to identify elemental concentrations within oil.

This testing method measures wear metals, contaminants and additive elements in parts per million (PPM). Spectrographic analysis helps identify:

• Wear metal composition
• Coolant contamination
• Dust contamination
• Additive depletion
• Cross-contamination between lubricants

Because the spectrometer can only detect and read particles smaller than 5 µm, it is most effective when combined with microscopic analysis, which identifies larger wear particles and particle morphology. Together, these testing methods provide highly accurate condition monitoring and early fault detection.

In the early stages of failure, larger wear particles are produced. These particles pass through the spectrometer undetected. They only become measurable after circulating long enough to be ground into fine debris. As they move through bearings, gears, and other components, they can damage equipment that was otherwise in good condition. By the time the spectrometer finally detects them, wear may already be widespread throughout the system.

When it becomes necessary to identify the main wear elements in larger particles, we can digest the particles in a strong acid solution. This process, known as acid digestion, allows the spectrometric analysis to become highly accurate. However, it is not the preferred method because preparation is slow and labour‑intensive, which increases the cost per sample. Acid digestion is, however, extremely effective for analysing grease samples. The entire grease sample is dissolved, allowing all elements to be fully measured and monitored.

Common Wear Metals Detected

These elements will give us a guide to the origin of the wear metals:

• IRON – gears, shafts, bearings and cylinders
• COPPER – bushes, bearings and bronze components
• ALUMINIUM – pistons and housings
• CHROMIUM – rings, cams and hardened surfaces
• LEAD & TIN – bearing materials
• NICKEL & TITANIUM – specialised alloys and components
• VANADIUM – chrome coatings, valve stems
• SILVER – Bearings, ring coating in some early engines and solder

Common Contaminants

• SILICON – Dust, sealant and gasket material, coolant and anti-foam additive
• SODIUM – Coolant additive, salt water contaminant or detergent additive

Additive Elements

Additives are blended into base oil to enhance performance for specific applications. Because of this, they are useful indicators for detecting cross‑contamination and, in some cases, assessing contamination levels.

• ZINC – Anti-wear, Extreme Pressure and anti-rust additive
• CALCIUM – Usually high in engine oils as TBN, detergent or dispersant additives
• PHOSPHOROUS – Anti-wear additive
• MOLYBDENUM – Anti-wear and friction reduction additives
• MAGNESIUM – Detergent, dispersant additives
• BORON – Extreme Pressure and coolant additive
• MANGANESE – Detergent additive and lightweight metal
• SULPHUR – Naturally occuring in base oil, anti-wear additive, extreme pressure additive and combustion by-product

Trend analysis is critical when interpreting spectrographic results. Sudden increases in wear metals or contaminants may indicate developing faults requiring immediate attention.

Stay within the manufacturer’s recommended limits, but treat any wear‑trend increase of more than 10% over comparable oil hours as an early warning. Always sample consistently and at regular intervals to maintain accurate trend data—this is the foundation of an effective monitoring program.

Viscosity Testing

The single most important property of lubricating oil. It directly affects film strength and lubrication performance.

Viscosity testing evaluates the oil’s resistance to flow, which directly influences many of its functional qualities. Because viscosity changes as the oil degrades, it serves as a reliable indicator of oil life and is a primary factor in determining when an oil change is required.

Oil viscosity is commonly measured at:

• 40˚C (100˚F)
• 100˚C (212˚F)

Monitoring viscosity changes helps identify:

• Oil degradation
• Fuel dilution
• Water contamination
• Oxidation
• Shearing
• Incorrect lubricant selection

Viscosity Index (VI)

The difference in viscosity at 40 °C and 100 °C is used to calculate the oil’s Viscosity Index (VI), which expresses how much the viscosity changes with temperature. A higher VI means the viscosity varies less between the two temperatures. High‑VI oils typically measure around 140, while low‑VI oils can approach zero.

Shearing

Viscosity can shear during use as the oil degrades, causing a drop in viscosity. In some engines, this shows up as increased oil consumption, indicating the oil is breaking down in service. Shearing is less common with today’s high‑quality oils, but using multi‑grade engine oils (such as 15W‑40) in certain high‑performance hydraulic systems can cause immediate viscosity loss.

In used‑oil analysis, our main focus is how far the viscosity has shifted from the new‑oil value. As a general guideline, a change of ±10% to 20% from the original viscosity—depending on operational standards—is a strong indicator that an oil change is due.

Causes of Viscosity Increase

• Particle contamination
• Oxidation
• Sludge formation

Causes of Viscosity Decrease

• Fuel dilution
• Lubricant shearing
• Chemical contamination

Viscosity should always be checked when assessing oil condition. Significant viscosity movements is a strong indicator that corrective action or oil replacement may be required.

Improve Reliability with Professional Oil Analysis

Regular oil analysis testing allows businesses to detect problems early, reduce maintenance costs and improve machinery reliability.

At Clean Oil Services, we provide advanced oil testing, condition monitoring and lubrication management solutions tailored to industrial, mining, transport and heavy equipment applications.

Contact Clean Oil Services today to order an oil sampling kit or discuss professional oil analysis testing services for your equipment.