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What Causes Diesel Bug and Other Forms Of Fuel Contaminates?

Diesel Bug

Diesel has within it an inherent bacteria which if not treated can grow into a dark slime that is commonly known as 'The Diesel Bug'.

The Diesel Bug grows rapidly if any water is present in your fuel tank as it will use this as a catalyst for growth, even a very small amount of water will help create enough bug to block an engine fuel line. I have come across around only 100ml of water in a tank which grew about 50ml of bug and a bit of a swell out at sea caused it to be sucked onto the fuel inlet pipe and block the fuel line. Even these small amounts of bacterial growth can prove disastrous.

< Diesel

< Bacterial Growth (Diesel Bug)

< Water

Water can get into your fuel tank in several ways, starting with the most common;

  1. Condensation - will produce small amounts of water over time (especially if boat unused) enabling bacterial growth.
  2. Fuel Filler Cap - The cap not being fitted correctly or a damaged rubber 'o' ring letting water into the fuel tank.
  3. From Fuel Stations - Fuel stations suffer from water build up as well and if not noticed will end up in your tank.
  4. Human Error - Somebody mistaking the diesel tank for the water tank! (more common than you would think).

Treating your fuel tank with a preventative, such as Marine 16's Diesel Bug Treatment, will keep the diesel bug at bay but will not remove the water from your tank and if forgotten bacterial growth will start forming again. If you already have signs of bacterial growth, treating it will stop more forming but what remains will stay in your fuel tank until your engine sucks it up blocking lines and fuel filters.

Getting Diesel Clean Machine to suck out the water and diesel bug bacterial growth from your fuel tank will prevent any further breakdowns through fuel starvation. Treating your fuel at each fuel fill up after that will keep the bacterial growth at bay and keeping your fuel tank full will help reduce condensation build up.


Diesel deteriorates over time and this produces a sediment which is heavier than diesel so will drop down to the bottom of the fuel tank. Over a long period this builds up and forms a sediment layer which looks a lot like mud or silt and if it was not for the fact that a boat moves around a lot it would probably stay there and not cause too much harm.

Unfortunately when the fuel is stirred up the sediment will lift and suck up into the fuel filters where it will gradually block the filter elements. A sign of this dirty fuel is if your fuel filters are very black when inspected, or in extreme cases have this black 'mud' embedded into the filter element.

Getting Diesel Clean Machine to removes this sediment turning dirty fuel to clean so will prolong the efficiency and flow of your fuel filters and can make a noticeable increase in performance from your engine.

Rust - Oxidization

Metal fuel tanks over time will start to rust internally (normally due to condensation) and the rust produced will drop off and fall to the bottom of the fuel tank where it will lay until stirred up and then be sucked into the fuel lines and fuel filters.

This will build up until the filter is completely blocked and your engine fails. Using Diesel Clean Machine will remove the dirty fuel from your tank and enable you to carry on using your boat until you replace your fuel tank.