109Fact Sheet No.

Bacteria / FungalGrowth in Diesel Fuel

What causes this problem?

For bacteria to propagate they require somewhere to live as well as a food source and these conditionscan exist in any fuel system. There is some water present in all fuel tanks, due to condensation, and thiswater will drop to the bottom of the tank to form a fuel/water interface.

The bacteria spores are airborne and can enter the fuel system any time the system is open to theatmosphere. This can happen, if the spores are present, at the time of refuelling. They may also be presentin the bulk fuel supply, having entered the bulk tank/s at the time of fuel delivery into the storage tanks atthe service station, a commercial installation or marina.

If there is any moisture present in the tank, from condensation, vehicle washing, or from any othersource, then there is an ideal environment for the bacteria to live and grow. Once they have entered thebulk installation tank or the vehicle or equipment service tank, and moisture is present, the bacteria willlive at the fuel/water interface and feed on the fuel itself and their colonies will grow rapidly.

What are the symptoms of bacteria problems?

The bacteria colonies form a slimy material as they excrete waste. This slime ranges in colour from khakithrough dark grey to black. This material has a rubbery-stringy feel and appearance, and can be slightlytenacious before it breaks away from the parent colony. As the slimy material breaks away, it migratesthrough the fuel in the tank where it is picked up in the fuel suction system. This can then result in blockedfuel filters and even clogged fuel lines, causing fuel starvation and loss of engine power.

In extreme cases, wear of injectors and fuel pump elements may occur as these components rely oncontinuous fuel flow to achieve internal lubrication.

When bacteria are detected in a vehicle or equipment fuel system the tank and fuel lines should bethoroughly cleaned, if at all possible, prior to any attempt to treat the fuel. While treatment of the fuel will killthe bacteria, failure to thoroughly clean the tank and lines will usually just lead to continual problems as moreof the slimy deposits are detached and prematurely block the filters.

Clearing the system

If problems occur with continual fuel filter blockage and the deposits are of the slimy nature describedabove, the fuel tank itself should be inspected to determine if there is mild or heavy bacteria infection inthe system.

Mild infestation – Where there is only a mild problem with bacteria, or if the tank is difficult to remove, itmay be possible to treat the fuel with a suitable biocide to kill the infestation. The fuel tank should bedrained to remove the contaminated fuel and any water, and the tank flushed with clean fuel. The fuelbiocide should then be added at the recommended treat rate and the tank filled with fresh fuel.

While this treatment will kill the bacteria, it will not dissolve the deposits. They will continue to dislodgeand be picked up in the fuel filter. The filter can then be replaced as it becomes blocked with the dislodgedslime. In the case of such mild infestation, the deposits should all be dislodged from the tank walls in arelatively short period of time and one or two filter changes may be all that is required to clear the systemof these deposits.

Heavy infestation – If the fuel system is heavily contaminated with bacteria it will be necessary to removethe fuel tank and lines and thoroughly clean the system to kill the infestation and remove the deposits. Asuitable biocide, used at a higher concentration in diesel fuel, or methylated spirits are effective agents forkilling the bacteria infestation.

Once the tank has been treated in this manner and the bacteria killed, the tank should be thoroughlycleaned, either manually or by continual flushing with diesel fuel, to remove all traces of the bacteriadeposits. After the tank has been cleaned it should be finally flushed with clean fuel to remove any traces

Diesel fuels, both in storage and in service, from time to time can suffer problems of fungal orbacteria growth. The most common bacteria growth is Cladisporium Resinai. This bacteria, whenpresent, lives at the fuel/water interface which may exist in either storage tanks or thevehicle/equipment service tanks. If not controlled, it can cause problems with fuel supply to theengine, resulting in poor engine performance, difficulty in starting, or even complete stoppage of theengine in service.

Technical Bulletin

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109

Bacteria / FungalGrowth in Diesel Fuel

of the cleaning additives used. Similarly, the fuel lines and the rest of the fuel system should also becleaned, as the bacteria will have spread throughout the system.

Once the system has been thoroughly cleaned, the tank can be refitted and the fuel system reassembledwith new filters.

Note: Biocides, by their very nature, are designed to kill bacteria and as such are not pleasant substancesto work with. Hence, we at Nulon recommend the use of methylated spirits, which is best used with thetank removed. After draining and removing the tank add sufficient methylated spirits so that rolling thetank around will allow the methylated spirits to make contact with all internal surfaces, seams etc. (If thetank cannot be removed it will be necessary to completely fill the tank with methylated spirits.) Then drainthe methylated spirits and thoroughly flush the tank with hot water, as heat also kills the bacteria. Addsome further methylated spirits to get any residual water out of the tank and flush the tank several timeswith fresh diesel fuel. Clean the fuel lines in a similar manner. Reinstall the tank and fit a new filter.

Protecting the fuel system against future attack

Once the fuel system has been cleaned of all traces of the bacteria, care should be taken to guard againstany possible future bacteria attack. To minimise the possibility of future problems the fuel tank should bekept full of fuel wherever possible, especially during periods of extended shut down. Any moisture orwater should be periodically drained from the tank and fuel filters.

The tank should be protected from any possible moisture ingress, especially during vehicle cleaning. Werecommend regular use of a quality fuel treatment such as Nulon DIC Diesel Injector Cleaner. Nulon DICis a complete fuel system treatment. It will help keep the entire system clean – it maintains fuel integrityduring storage, it improves fuel economy, it reduces black exhaust smoke, it protects against corrosion andit lubricates the fuel pump. Nulon DIC, by keeping the fuel within specification and keeping the systemclean, provides a less friendly environment for bacteria. Using a biocide on a regular basis is of little benefitas the bacteria quickly become resistant.

These simple steps should assist you in avoiding any bacteria problems and provide reliable service fromyour vehicle, pleasure craft or equipment.

Q. How do I recognise the bacteria/fungi?

A. Generally it is first noticed when changing fuel filters. It has a slimy consistency and ranges incolour from khaki to black. It is rubbery and stringy to the touch.

Q. How do I know when I have bacteria/fungi in my diesel tank?

A. If it is in a storage tank that does not have a filter fitted, you may not be aware of infestation untilthe filter/s of the vehicle or machine to which fuel has been transferred become blocked. If the tankis fitted with a filter, delivery will be slow because of filter plugging. If a vehicle or machine isinfested the first sign will be poor running due to fuel starvation, because of filter plugging.

Q. Can I overcome the problem by simply using a biocide to kill the infestation?

A. No! While a biocide will kill the infestation, the dead material is still in the tank and will continueto create blockage and supply problems. The tank needs to be drained and cleaned.

Q. How do I guard against a problem with bacteria/fungi?

A. It is impossible to completely avoid infestation. However, there are precautions that can be takento minimise the chance of infestation. They are:

• Keep fuel tanks full, particularly through periods of extended shut-down

• Periodically drain water from the bottom of tanks, as bacteria cannot survive without water.

• Protect the tank from any possible water ingress.

• Purchase fuel from large-volume sites whenever possible as the fuel is fresher.

• Purchase fuel from reputable suppliers.

• Try to avoid purchasing fuel immediately after a supplier has received a delivery (this will allowagitated water and contaminants to settle).

Phone: +61 2 9450 1791

Freecall: 1800 67 99 22

Fax: +61 2 9450 2448

Freecall: 1800 67 99 70

Website: www.nulon.com.au

Email: technical@nulon.com.au

Nulon Products Australia Pty Ltd

Unit 1, 4 Narabang Way

BELROSE NSW

AUSTRALIA 2085

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