Have You Ever Wondered Why Changing Your Engine Oil Is So Important?
Regularly changing your engine oil is more than just a recommended maintenance task—it’s a crucial part of ensuring your vehicle's engine runs smoothly, efficiently, and reliably. Oil serves as the lifeblood of your engine, performing several vital functions such as lubrication, cooling, cleaning, and preventing internal corrosion. 
Over time, however
, engine oil degrades as it gets exposed to heat, oxygen, friction, and contaminants. This degradation not only reduces the oil’s ability to protect the engine but can also lead to engine damage if left unaddressed.
One of the key indicators of oil degradation is the Total Acid Number (TAN), a measurement that helps determine how acidic the oil has become as it ages. As oil breaks down, it reacts with the heat and oxygen in the engine, forming acidic compounds that increase the oil’s acidity level. This rise in acidity can have detrimental effects on the engine’s performance and longevity. Understanding how oil degrades, and the role of TAN is essential to understanding why regular oil changes are critical for maintaining engine health.
Why Regular Oil Changes Matter
As the oil ages, its ability to lubricate the engine and reduce friction diminishes, which can cause several issues, including:
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Increased Wear and Tear: When oil becomes too thick or loses its lubricating properties, it causes increased friction between engine parts. Over time, this can lead to the wearing down of critical engine components such as pistons, cylinders and bearings, resulting in costly repairs and reduced engine efficiency.
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Corrosion: As oil degrades, its acidity increases. High TAN levels mean the oil is becoming more acidic, which can lead to corrosion of engine parts. This is particularly problematic for metal components, which can rust or develop pits, compromising their integrity and performance.
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Sludge Formation: The breakdown of oil can lead to the formation of sludge, which can clog critical oil passages in the engine. When this happens, oil can no longer circulate efficiently, leading to overheating, reduced lubrication and increased risk of engine failure
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Loss of Cooling Efficiency: Engine oil also plays a key role in absorbing heat and preventing the engine from overheating. Degraded oil, however, becomes thicker and loses its ability to flow properly, diminishing its cooling capabilities and putting extra strain on the engine.
The Role of TAN in Oil Degradation
TAN is measured by titrating a sample of the oil with a base, typically potassium hydroxide (KOH) or sodium hydroxide (NaOH). The amount of base required to neutralise the acids in the oil sample directly correlates with the oil’s acidity level. The higher the TAN value, the greater the acidity in the oil, and the more degraded the oil is.
The Analytical Titration Process for Measuring TAN
Measuring TAN is crucial for understanding the condition of engine oil and determining whether it’s time for an oil change. The titration process used to measure TAN involves adding a base to the oil sample to neutralise the acids, and it provides a precise way to determine the oil's acidity.
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Sample Preparation: A precise amount of used engine oil is collected for testing. The oil sample is typically weighed and dissolved in a solvent to make it easier to titrate. The solvent often used is a mixture of alcohol and toluene, which helps separate the acidic compounds for better titration accuracy.
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Titration with Base: The sample is titrated with a standardised solution of a base, such as potassium hydroxide (KOH) or sodium hydroxide (NaOH). The base neutralises the acids in the oil sample, which raises the pH level of the solution.
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Monitoring the Endpoint: The titration process is monitored using a pH indicator, typically phenolphthalein, which changes colour as the pH of the solution shifts from acidic to neutral. The endpoint is reached when the solution becomes neutral or slightly basic, indicating that all the acidic compounds in the sample have been neutralised.
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Calculation of TAN: The TAN is calculated by measuring the volume of base required to neutralise the acids in the oil sample, the concentration of the base, and the weight of the sample. The formula used is:
TAN=V×N×56.1W\text{TAN} = \frac{V \times N \times 56.1}{W}TAN=WV×N×56.1
Where:
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V = Volume of titrant used (in mL)
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N = Normality of the titrant (concentration in equivalents per litre)
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W = Weight of the oil sample (in grams)
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56.1 = A factor relating moles of KOH to acid groups in the sample.
The Role of Reference Materials in TAN Measurement
Reference materials are substances with known properties, such as a specific acid value, that can be used to check the accuracy of the titration process. In the case of TAN testing, reference materials serve the following purposes:
Standardising the Titrant: Reference materials are used to standardise the titrant solution before testing the oil sample. A reference material with a known acid value is titrated with the base, and this confirms that the titrant has the correct concentration.
Calibration of Equipment: Reference materials help calibrate the titration equipment, such as burettes and pH meters. This ensures that the equipment is providing accurate measurements during the titration process.
Accuracy Verification: After performing the titration on the oil sample, a reference material with a known TAN is titrated in parallel to verify the accuracy of the results. If the results from the oil sample match the known value of the reference material, it confirms the procedure was executed correctly.
Quality Control: Reference materials ensure consistency across different batches of oil samples and over time. By using reference materials with certified values, laboratories can maintain reliable and reproducible results, helping vehicle owners make informed decisions about their oil change schedule.
Industry Insight: The Growing Importance of Oil Analysis
In recent years, the automotive industry has seen a growing emphasis on oil analysis as part of proactive maintenance programs. Manufacturers are increasingly relying on regular oil testing to determine the optimal time for oil changes. 
Oil analysis not only helps extend the life of the engine but also improves fuel efficiency and reduces emissions by ensuring that the engine is always operating with clean, effective oil.
With advances in oil technology, oils last longer and endure higher temperatures than ever before. However, even the best oils degrade over time, and routine testing of parameters like TAN is necessary to determine when oil replacement is required. By monitoring oil quality car owners can make decisions to prevent costly engine repairs and maximise the lifespan of their vehicles.
Conclusion
Using reference materials to calibrate the titration process ensures the accuracy and reliability of TAN measurements, which in turn helps preserve engine performance and reduce emissions. In today’s competitive automotive industry, oil analysis is becoming an increasingly important tool for preventing damage, improving fuel efficiency, and extending the life of vehicles. Regular oil changes and oil analysis are more than just maintenance tasks—they are investments in the long-term health of your engine.
ARO Scientific Certified Reference Materials
ASTM664-24 - Standard Test Method for Acid Number of Petroleum Products by Potentiometric Titration: describes a potentiometric titration, and a pH electrode
indicates the endpoint. The sample colour does not affect this method. It is suitable for petroleum products, lubricants, biodiesel, and biodiesel blends.
ASTMD974 - Standard Test Method for Acid and Base Number by Colour-Indicator Titration: describes a photometric titration which uses an optical sensor for the indication. This test method is well-suited for light-coloured petroleum products and lubricants.