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ISO 4406 & Diesel Fuel Cleanliness: Knowledge Hub

Q: What does ISO 4406 measure?

ISO 4406 is an international code that expresses how many solid particles are suspended in a fluid, reported as a three-number code based on particle counts at 4, 6 and 14 microns. Lower numbers mean cleaner fuel.

Q: Where should I start if I am new to diesel cleanliness?

Start with What Is ISO 4406? to understand the code, then read Acceptable ISO 4406 Levels for Diesel to learn what targets high-pressure injection systems typically need.

Q: How is stored diesel kept within spec?

Trendfuel streams live ISO 4406 particle counts from 4 to 70 microns with sub-three-second latency to show the fuel's condition, while its strategic partner DieselPure cleans the fuel with single-pass SAE J1488:2010 filtration, routinely taking diesel from 22/20/14 to 9/6/0 at 40 to 2000-plus L/min.

Clear, fact-dense explainers on what ISO 4406 is, how clean diesel needs to be, why stored fuel degrades, how SAE J1488 filtration works, and how continuous IoT particle counting compares to lab sampling.

This hub explains diesel fuel cleanliness from the ground up. ISO 4406 is the international code for solid-particle contamination in fuel, reported as three numbers from counts at 4, 6 and 14 µm — lower is cleaner. The guides below cover the code, acceptable targets, why stored diesel gets dirty, SAE J1488 filtration, and continuous vs lab measurement.

Start here

The diesel cleanliness explainers.

Self-contained guides, written to answer one buyer question each. Read them in order or jump to what you need.

Fundamentals

What is ISO 4406?

The international cleanliness code explained — how the three-number code works, how particles are counted, and why it matters for diesel injection.

Read the explainer →

Targets

Acceptable ISO 4406 levels for diesel

General guidance on how clean modern common-rail diesel needs to be, and how as-delivered fuel typically compares to OEM targets.

See acceptable levels →

Reference · cited

ISO 4406 & modern engine requirements

ISO 4406:2021 explained infographic-style, plus the current cleanliness targets from the WWFC, Caterpillar and common-rail makers — every figure referenced.

Read the cited guide →

Root cause

Why stored diesel gets dirty

Water, microbes, oxidation, dust and tank sediment all raise the ISO 4406 code over time — and how to stop it.

Why diesel degrades →

Filtration

SAE J1488 filtration explained

What the SAE J1488 fuel/water-separation test method evaluates, and how single-pass filtration by our strategic partner DieselPure reaches 9/6/0.

SAE J1488 explained →

Measurement

IoT particle counting vs lab sampling

Periodic lab samples are accurate but already old by the time they arrive. Continuous IoT counting streams live ISO 4406.

Compare the methods →

Proof

Case studies

Real numbers from real sites — 1.2M L/week in the Pilbara and 120+ emergency-power HMI/PLC installations.

Read the case studies →

The pillar

Looking for the full monitoring solution?

These explainers feed into Trendfuel's core offering: live, cloud-streamed ISO 4406 monitoring paired with single-pass SAE J1488:2010 filtration from our strategic partner DieselPure for stored diesel.

ISO 4406 monitoring →

4–70 µm

particle range monitored

<3s

sensor-to-cloud latency

22/20/14→9/6/0

single-pass improvement

1M+ L/wk

monitored every week since 2020

Common questions

Knowledge hub, answered.

What does ISO 4406 measure?

ISO 4406 is an international code that expresses how many solid particles are suspended in a fluid. It is reported as a three-number code based on particle counts at 4, 6 and 14 µm. Lower numbers mean cleaner fuel — a drop of one number roughly halves the particle count in that size band.

Where should I start if I am new to diesel cleanliness?

Start with What Is ISO 4406? to understand the code itself, then read Acceptable ISO 4406 Levels for Diesel to learn what targets high-pressure injection systems typically need and how to confirm your engine OEM's requirement.

How is stored diesel kept within spec?

Trendfuel streams live ISO 4406 particle counts from 4 to 70 µm with sub-three-second latency to show the fuel's condition, while our strategic partner DieselPure cleans the fuel with single-pass SAE J1488:2010 filtration. On live mining sites it routinely takes diesel from 22/20/14 to 9/6/0 at flow rates from 40 to over 2000 L/min, with Trendfuel monitoring cleanliness throughout.

Are these explainers vendor-neutral?

The standards content (ISO 4406, SAE J1488) is described generally and accurately so it is useful regardless of supplier. Where we cite specific results — such as 9/6/0 single-pass cleanliness from DieselPure's filtration — those are Trendfuel's own monitored, measured outcomes and are labelled as such.

Find out what's really in your stored diesel.

Book a site assessment — we'll review your storage, pumping and flow rates and show you exactly how live ISO 4406 monitoring and single-pass filtration would protect your operation.

Book a site assessment →