Contaminated Fuel – What happens when water gets in your diesel tank?

Although modern Diesel fuel injection systems have less moving parts than traditional mechanical systems they are more prone to damage due to the much smaller manufacturing tolerances.

Since Diesel fuel injection systems were first invented and used to control engine operation, water in the Diesel fuel has been the biggest contributor to the failure of such systems. Repairs are generally expensive due to the hi-tech nature of components and the amount of parts that can be affected by the contamination.

Microbes in the fuel

Microbes (bacteria & fungus) can grow and develop in the water-diesel interface. These microbes produce acids as a by-product of their day-to-day existence which can exacerbate corrosion of precision machined components within the fuel system. Once microbes have colonised a fuel tank, they will continue to multiply especially in favourable hot and humid conditions. There are a variety of in-tank treatments, such as biocides, which can be used to kill off the microbes, however if damage has already been done, a full system service will be required.  This would involve removing and professionally cleaning the tank, stripping, inspecting and replacing or repairing all system components such as pumps, injectors, rail, in-tank module, filtration system and associated fuel lines.

Even without the presence of microbes, the water in the fuel can still be highly damaging to the system. All Diesel fuel injection systems rely on the lubricity of the Diesel to lubricate and remove excess heat from the frictional forces generated by the various components. This is even more relevant to modern high pressure common rail systems where the tolerances are much tighter due to the extremely high pressures (ranging from 1,600 – 2,800 BAR and beyond).

What to do if you discover water in your system?

Ideally you want to understand how much water is in the system as the ratio of water to fuel will determine how quickly and how much damage will occur to the system. The Australian Standard Limit for water content is 200 PPM (Parts per Million) which equates to approximately 0.02% by volume. If you are unsure, it is recommended you cease operating the vehicle and get it towed to a Diesel Specialist who can take a sample from the tank as well as the filter. If picked up early you may get away with a system flush, however the longer the vehicle operates with the water remaining in the system, the worse the outcome will be. More often than not your local authorised Diesel specialist will carry a range of high quality remanufactured components which can save time and money. Often the price of such exchange components can be up to 70% less than new parts purchased from the vehicle dealer, yet they will still come with the same or similar warranty conditions.

Preventative Measures

Most modern Diesels have a warning system built into the fuel filter module which incorporates a water trap and a float which will bring up a warning light on the dash board. These systems are great, however if a large amount of water has been picked up whilst filling up your tank, by the time the system activates, damage may have already happened to the fuel injection system. Fitting a Secondary Filter module with its own water trap can provide a second line of defence which makes the vehicle system much more effective. A good quality Secondary Filter kit can range between $280 and $350 depending on the vehicle, which is a relatively small price to pay when compared to the inconvenience and cost of having your vehicle off the road for major repairs.

These filters are generally either 5 or 2 micron rated which will further protect your system against solid contaminants that may find their way into your tank. In addition it is recommended that fill your car up at Service Stations who have a higher turnover of fuel as the in-ground tanks are less likely to have residual water. Keep all receipts in case you do pick up a bad dose of fuel as this may then give you some recourse and may be required by your insurance company to assist with processing any possible claims.