LEM Diagnostics

LEM®—the driving force in engine diagnostics.

Download LEM® Data Sheet PDF

Working in conjunction with major engine manufacturers, oil companies and additive suppliers, Bureau Veritas has developed a new diagnostics technology that monitors the amount of soot buildup in diesel engines.

LEM – Light Extinction Measurement® – is quick, accurate and economical and offers significant advantages over older methods for measuring soot .

Simply stated, LEM® lets us identify and monitor soot levels within an engine’s lubricant, avoiding the harmful effects that it can produce over time. The speed, accuracy and affordability of our new LEM® technology offers significant advantages over older testing methods.

Get more miles from your engine.

How does LEM® work? We begin by analyzing a sample of used engine oil. After accurately measuring the amount of soot that is present within an engine, we cross-reference these levels against OEM-recommended maximums for particular motors. This analysis is performed by directly reading oil samples that are not altered through dilution or burning—a key factor for accuracy. LEM® overcomes the drawbacks associated with other lab diagnostic methods by quickly and economically determining a lubricant’s remaining service range. Moreover, it is accurate for today’s newest engine technologies as well as the most advanced lubricants and fuels. LEM® also accommodates the higher levels of soot that are produced in some of today’s newer engines. This fast, inexpensive technology can extend the life of a diesel engine and save thousands of dollars by preventing premature wear.


LEM® leaves other diagnostics in the dust.

While there are a number of alternative technologies for engine diagnostics, they all carry significant drawbacks in time, money or accuracy:

Infrared (IR) testing
This technology was acceptable for past emission levels. However, future soot levels in diesel engine lubricants will routinely exceed IR’s capacities and capabilities. Beyond these limitations, IR results also tend to be erratic and unreliable.

Thermogravimetic Analysis (TGA)
The need to regularly monitor engine soot levels means that these expensive, time-consuming tests are beyond the reach of many truck and fleet owners.

Total Solids
This technology determines the total content of contaminants in oil, yet it cannot definitively measure soot levels. Instead, it measures the combined amount of contaminants, including dirt, wear metals, and even additives. Additionally, this testing method uses solvent/extraction, which carries an environmental concern and drives-up costs due to waste disposal expenses.


LEM®—the speed of IR with the accuracy of TGA.

LEM® provides the key data to help you determine the most effective and economic oil change intervals for the engines within your fleet. Moreover, it improves fleet management and prolongs the service of your engines by helping you:

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  • Maximize the service of your lubricants
  • Maximize engine performance
  • Determine optimum oil change intervals



LEM® readings:

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  • Give no false-positive, high-soot readings caused by conditions unrelated to fuel soot (unlike IR testing)
  • Require no solvents, standards or reference oils—reads directly from oil samples


Once the LEM® Analyzer has scanned the sample, Bureau Veritas’ high speed LEM® computer program examines the results and automatically calculates the soot percentage.


Download a LEM® Analysis PDF