What is diesel bug and how to avoid it

A ‘diesel bug’ is microbial bacteria. It thrives in warm temperatures although it can be active in any temperature between 5C and 70C. More tropical locations where the ambient temperature is generally around 30C are worst for the encouragement of a diesel bug.

If at all possible try to insulate your Diesel tanks (using fire insulation material makes sense) so as to better regulate their temperature. Also, if running a heater below decks keep temperatures within reasonable parameters, especially if you are no on the boat (for example in winter).

Modern biodiesels make the problem worse introducing a lifespan for fuel which is forever shortening. 

If allowed to grow a diesel bug will cause havoc - and expensive havoc at that. Usually, the evidence of a bug will be a poorly running or intermittent firing engine or excessive smoke. However, the best ways to protect yourself from contaminated fuel are simple and effective. 

To best protect your fuel system and avoid very expensive maintenance later consider implementing these simple procedures;

  1. Source good quality, clean fuel
  2. Filter fuel before it enters the tank. Make sure the filter is clean and in good condition.
  3. Keep water out of the fuel. This means protecting the fuel tank’s main cap and opening but also consider installing a desiccant air filter on the breather pipe to the fuel tank. A RACOR filter will help keep fuel clean and uncontaminated too. Try to keep your fuel tanks full. This will restrict the amount of air in the tanks and so limit any condensation that may occur.
  4. As part of your maintenance plan periodically check your tanks for black sludge (the evidence of a diesel bug). You can check pipes too, but the best way is to draw off some fuel from the tanks. If this isn’t possible, invest in a small hand pump and a length of pipe. You can use this to reach the bottom of a tank and remove water or sludge.
  5. Consider using additives to help keep your fuel free of microbial bacteria.
  6. You can check your tanks internally using an endoscope introduced through the inspection cap.
  7. Regularly change fuel filters
  8. If you have small tanks, consider draining remaining fuel from your tanks and restocking in the new year. Alternatively, keep the tanks full and introduce the appropriate additives, keep the tanks full and try to keep the temperature between 5c and 10C.

If you do get a diesel bug you’re going to need to dispose of all contaminated fuel carefully (and responsibly) and clean out all pipes, tanks and filters. In bad cases your injectors or fuel pump may also need cleaning or replacing. Then, you’ll need to introduce some form of chemical treatment. The whole cost can run into hundreds - or even thousands dependent on your boat and the scale of the problem.

In the first instance, make a plan and then, if you have a problem, consult a trusted expert.

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