Technical Feature

Diesel Fuel Contamination

When we encounter diesel vehicle running issues or an engine fault light, often this is related to fuel contamination.

When fuel contamination is encountered it is most commonly due to water in the fuel supply but it can be from other contaminates such as debris, rust or algae growth in the fuel.

Earlier diesel engine fuel systems with their more forgiving tolerances were able to cope with fuel contamination better than the high tech finely engineered Common rail Systems we have these days. This doesn’t mean they are immune to contaminates in fuel such as water but modern Common Rail Systems are much less tolerant.

Water is by far the most prevalent and most damaging contaminate we encounter in modern Common rail diesel fuel systems, the main purpose of the fuel filter is to remove harmful particles from fuel. Although, some fuel filters have a water controlling coating on the filtration medium, water will still travel through fuel filters especially at the flow rates of Common Rail Fuel Systems.

Water causes catastrophic damage to supply pumps, rails, high pressure lines, injectors and many other components. Water does this firstly by causing a lack of lubrication and very quickly (sometimes within hours) causes components to rust. Rust is very abrasive and damages most of the components of the fuel system and it will require all parts of the fuel system to be replaced. Rust particles can be submicron in size and therefore will travel through the best fuel filters.

The Common Rail Fuel System circulates fuel at a very high rate so as to help facilitate cooling of components and fuel. Flow rates are around 70 liters per hour, with the fuel cycling from the tank and through the fuel system and then back to the fuel tank. In the event of an issue, the debris from component damage is very quickly circulated through the whole fuel system, so when undertaking a repair, no damaged part or debris can be allowed to remain in the system as they will damage new components.

It is important to first collect a fuel sample from an area where water and particles would be most likely to gather, for example the fuel filter base or fuel tank pick up canister.

The sample should be put into a small clear glass bottle 100ml approx. 25-30mm diameter. The sample can then be inspected visually, or tested with a test strip or paste.

Use a small high energy LED torch to enable metal particles to be seen as they will appear larger and become much more visible to the naked eye with the LED light.

Darker red/orange particles may indicate rust from a rusty fuel tank found in earlier vehicles, or an aftermarket steel fuel tank that has been fitted where a poly tank was original or this rust could simply have been pumped in during a routine fill.

Note: Very small metal particles can travel through the fuel filter and once inside the fuel system it will continue to cause an increasing amount of abrasive debris to form.

The bright shiny metal is from wear to components such as injector spindle or push rod, supply primary trochoid pump gear set and cam block.

The amount of this metal can indicate the amount of wear that has taken place up to now and how catastrophic the damage is. In a 100ml bottle this can vary from 20-100 particles to many thousands, at this point we can gather together particles that can’t be seen even with the LED light using a small super strong Neodymium Rare Earth magnet.

Held against the side of the test bottle particles will quickly gather at the area around the end of the magnet, this will show to what extent the sample contains metal particles.

Diesel fuel is produced via the fractional distillation of crude oil between 200°C (392°F) and 350°C (662°F). These production temperatures mean that no significant water or biological contaminates are likely to originate from diesel fuel produced at refineries, the contamination could have occurred during haulage or storage, with the fuel becoming contaminated with water, rust and algae/ bacteria spores etc.

Cladosporium Resinae (algae) appears to be one of the more common growths found in Diesel, whilst biological growth can be a problem; the water itself is a bigger problem. A biological growth is often an indication of water within the tank. The algae will grow at the junction of diesel and water layer and will multiply very rapidly and this can block filters etc.

We can find other contaminates in the Diesel sample such as bitumen residue, carbon from the Diesel fuel – but in this primary inspection we are looking at introduced contaminates that may have damaged the fuel system.

Testing the vehicles Injector Return Volume allows us to inspect some aspects of Injector operation using either an injector return volume measuring kit for magnet valve injector types or Piezo injector test kit. Both kits are used to indicate injector damage via return volume or pressures.

When we combine injector return leakage test, fuel sample results, injector compensation figures and system pressure control ability, this will give us confirmation that the system is contaminated and that repairs are required.

Responsive Engineering says the most effective method used to protect a diesel fuel system is to have a Diesel Water Watch unit fitted. These systems detect very small amounts of water, typically between 5-10ml.

Diesel Water Watch has a visual and audible alarm which activates as soon as water is detected; prompting the driver to pull over and assess the level of contamination caught in the glass bowl and drain it.

This prevents the contamination from entering the sensitive components of the Common Rail Fuel System.

If the warning alarm continues to reoccur you may need the fuel tank removed and cleaned.

The Diesel Water Watch system works by utilising an electronic probe suspended in the fuel. The unit removes water and debris heavier than the fuel using a diffuser system to help separate the debris and then retains both the water and particulates in the bottom of the glass bowl. The pressure of the fuel flowing rapidly through the Diesel Water Watch holds contamination particles below the flow of the fuel, where it can be easily removed.

No filters are used, so there is no additional restriction on fuel flow or pressure, and no ongoing maintenance. The Diesel Water Watch was not only invented in Australia, but is also made in Australia and comes with a lifetime warranty. Detailed fitting instructions and bracket kits are available for most of the popular diesel vehicle applications in Australia.

For more information visit or call (02) 6280 4334

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