Diesel bug has become a concern for many boat owners in recent years. The condition occurs when a mixture of bacteria, algae and mould contaminates the storage tank and then breeds - creating a slimy, film-like coating that lives inside fuel systems.

Water in the tank is a common breeding ground for diesel bug; the microbes feed on fuel, but need water to live and grow. And the waste created from the bug can block filters (leading to fuel starvation) or even worse, worn injectors and engine failure.

Biodiesel fuels and water separation:

With biodiesel fuels increasingly being used as standard in the marine industry, diesel bug is becoming more widespread. Within the UK, most fuel produced is ?B7? (which means that seven per cent of biofuels content in the diesel). The higher the proportion of biofuel content, the harder it is for traditional filtration systems to separate water from the fuel ? and where there is more water in fuel, there is greater potential for diesel bug to grow.

That?s where fuel polishing systems, such as Racor?s fuel conditioning modules, give boat owners an advantage. By polishing fuel regularly and keeping the tank water free, the chances of getting diesel bug are vastly reduced. And even if the bug is growing in the tank, fitting a conditioning system will filter harmful detritus out.

Using fuel polishing systems to tackle diesel bug:

A fuel polishing and conditioning system works like a dialysis machine. The fuel line goes through the main filter to the engine; but you can also put a separate loop, filter and pump onto the system.

When a boat is moored up and the engine is offline, the fuel conditioning system will take fuel out of the tank, pump it through the filter and put it back into the tank again. As fuel pumps through the filter, the system removes any moisture and contaminants ? which typically means less maintenance, and helps the engine to last longer.

There are a range of fuel conditioning systems available on the market. These range from reasonably priced systems with a small pump and filter, through to more sophisticated and expensive options with moisture sensors, automatic drains and timers. But the principle is the same. Racor?s fuel conditioning module is a combined fuel filter and water separator; housing a low-pressure fuel pump and components in one self-contained unit, the system supplies clean dry fuel to the fuel system.

It?s worth bearing in mind that polishing systems can operate with a small filter. They can also be put on a timer, to run overnight or whilst the owner is away from the boat. And they really come into their own where boats are affected by, or at risk of, the bug.

Another option is to put an additive into the tank, either with or without a polishing system. This will kill the bug and stop it growing.

Rectifying the problem of diesel bug contamination can result in major work and can be very costly. In some instances the boat owner can be 'lucky' and use a specialist tank cleaning company to sort things out; this typically results in a bill of a few hundred UK pounds (or equivalent).

However, if the tank can't be cleaned, structural modifications may be needed to remove or replace tanks - costing many thousands of pounds. So the more preventative action that boat owners take, the better their chances of avoiding or reducing diesel bug, and its associated costs.