Keeping the diesel bug at bay
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Thu Jun 1, 2017 at 8:57am

Bacterial Contamination

Diesel Bug as it is more commonly known is becoming a much more common problem particularly in BULK storage tanks, marine craft and agricultural equipment. 


It’s impossible to prevent microbes entering fuel tanks and systems. However, the presence of water is a key factor in determining the rate and extent of microbial growth.

Condensation or free water suspended in the fuel clings to the tank walls or slowly sinks to the bottom of the tank, and microbes will grow at the fuel/water interface. They feed off dissolved oxygen and nutrients in the fuel, and their growth creates more water as they break down the hydrocarbons. Slime is formed, which blocks filters and restricts fuel lines. The resulting sludge is acidic, and can corrode vital engine components such as fuel pumps and injectors. 


Symptoms of fuel contamination

Engines can function with a surprisingly high amount of microbial growth in the fuel, so the chances are you’ll see the warning signs before it gets to the point that the engine actually fails. Symptoms include poor starting, fuel starvation, erratic running and black smoke from the exhaust. Even at this point, changing the filter should be enough to get you home. But that won’t solve the problem. You’ll need to eradicate the bug and, if necessary, have the tank and all the associated pipe work flushed, cleaned and treated with biocide. For bulk storage tanks the fuel would need biocide treatment with flushing of all pipework and external filtration to remove all contamination.   

There has been much discussion and misunderstanding of algae in diesel fuel. Algae need light to live and grow. As there is no sunlight in a closed fuel tank, no algae can survive, but some microbes can survive and feed on the diesel fuel.

These microbes form a colony that lives at the interface of fuel and water. They grow quite fast in warmer temperatures. They can even grow in cold weather when fuel tank heaters are installed. Parts of the colony can break off and clog the fuel lines and fuel filters.

Water in fuel can damage a fuel injection pump; some diesel fuel filters also trap water. Water contamination in diesel fuel can lead to freezing while in the fuel tank. The freezing water that saturates the fuel will sometimes clog the fuel injector pump. Once the water inside the fuel tank has started to freeze, gelling is more likely to occur. When the fuel is gelled it is not effective until the temperature is raised and the fuel returns to a liquid state.

There are companies and marine engineers available who will clean the fuel in a process called "Fuel Polishing" Fuel polishing is designed to eradicate the bugs and bacteria which accumulate in stored diesel and oil.

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Heath | Wed Jun 7, 2017 at 3:54am
Is fuel polishing a chemical process ? and if so could a filter with that chemical contained be put into the fuel line to filter and never have the problem again ..
Venetian Marina | Wed Jun 7, 2017 at 8:59am
Dear Sir,Thank you for your comment. The process for fuel polishing is as follows. 72 hours before the treatment pour into the fuel tank the diesel "treatment", and leave. After 72 hours the fuel polishing my start. This is special equipment which comprises of an electrical fuel pump and two filters. This circulates the fuel through the filters and the fuel tank thus removing the "bug" and contamination. You can purchase a fuel treatment additive to put in the diesel tank each time you re fuel to prevent this issue. There are some suppliers of diesel on the canal network who sell diesel which is FAME treated so the diesel bug can not form.
David Mitchell | Mon Jan 25, 2021 at 4:49pm
Great guide. There's not an awful lot of open reference online to diesel bug and what you can do to keep it at bay. It's always a good choice to get a diesel fuel testing kit to check if you have contaminated diesel or not.

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