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An overview of 342 – diesel quality and its importance

by John Evans B.Sc. MLA II – diagnostic manager, WearCheck


SANS 342:2016, the South African National Standard, serves as the governing document for diesel quality in South Africa, outlining properties, testing procedures, recommended methods, and quality limits. Accreditation by SANAS 17025 and SABS ISO 9001 ensures reliable results from laboratories.

When determining diesel quality, it is important to use a laboratory that employs the correct test methods as dictated by the standard. It is also important to use a laboratory that is accredited by SANAS 17025 (South African National Accreditation System) and SABS ISO 9001. This ensures that the tests are carried out correctly, quality standards are met, and the results are reliable.

The quality of diesel in South Africa is often debated, with issues arising from poor transportation, handling, storage, and corruption, leading to engine problems caused by contaminated diesel. This article focuses on WearCheck’s Specialty Laboratory tests, instrumentation, and consequences of failing standards, including specified limits.

This Technical Bulletin looks at the tests to determine diesel quality that are carried out in WearCheck’s Specialty Laboratory, the instrumentation used and what the consequences of failing to meet the standard might be, along with the actual limits that are applied.

FLASHPOINT: Diesel flashpoint, the minimum temperature for ignition, doesn’t directly impact engine combustion but affects safe storage and handling. A low flashpoint can signal petrol adulteration or contamination by other substances, while high viscosity fuels may result in poor combustion. The SANS requirement is a minimum flashpoint of 55ºC.

VISCOSITY: Measured at 40ºC, viscosity indicates a fluid’s resistance to flow. Deviations from the SANS requirement of 2.0 – 5.3 centistokes may lead to wear, leakage, and combustion issues.

DENSITY: Density, the mass of a liter of fuel, influences energy content. Diesel must have a minimum density of 0.800kg/l at 20ºC. Deviations can affect engine power and fuel consumption.

SULPHUR: Sulphur content is vital; low-sulphur diesel is specified at 0.005%, while normal diesel is at 0.05%. High-sulphur fuels can harm engines, affect lubricant life, and hinder emission control systems. Legislation for ultra-low sulphur fuel at 10 ppm (CF2) is planned for July 2026.

DISTILLATION: Distillation measures the temperature range for fuel vaporization. Distillation at 90% recovery (T90) must not exceed 362ºC. Contaminations can be identified through characteristic distillation curves.

WATER: Water, both dissolved and free, can corrode components and reduce lubrication. Maximum allowable water content is 350 ppm, assessed through Karl Fischer titration and visual inspection.

TOTAL CONTAMINATION: Total contamination, measured through IP440, evaluates solid particulate matter. The maximum allowed is 24 mg of dirt per kg of fuel.

CETANE NUMBER (INDEX): Cetane number indicates diesel ignition quality. The SANS requirement is a minimum of 45. Low cetane fuels cause issues like knock, difficult starting, and increased emissions.

VISUAL ASSESSMENT: Visual assessment checks for free water, particulate matter, and diesel clarity. Deviations from standards can lead to failure.

FUNGAL AND BACTERIAL TESTING: Testing for microbial contamination helps identify potential issues and allows corrective actions.

BIODIESEL: Biodiesel, derived from renewable sources, has a maximum allowable content of 5% (B5) in diesel.

TOTAL ACID NUMBER (TAN) and PARTICLE COUNTING (ISO 4406): TAN, indicating fuel acidity, and ISO 4406 for particle counting are additional tests for fuel cleanliness.

OTHER TESTS: Tests like copper corrosion, calorific values, cold filter plugging point, cloud point, lubricity, carbon residue, ash, and oxidation stability can be outsourced if necessary.

ILLUMINATING PARAFFIN: Contamination with illuminating paraffin (IP) poses a threat, impacting viscosity, density, flashpoint, and sulphur concentration. IP doping is illegal and harms engines. SARS introduced a chemical marker for IP detection, and testing methods, including lateral-flow tests and GC-MS analysis, help identify IP presence.

In conclusion, maintaining diesel quality is crucial for optimal engine performance and longevity, emphasising the importance of regular testing and adherence to standards.

For further information, visit, email  or call WearCheck’s head office on +27 (31) 700-5460.

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This article is a summary of WearCheck’s Technical Bulletin 87: AN OVERVIEW OF 342 – DIESEL QUALITY AND ITS IMPORTANCE. To view the full article, please visit

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