Yachting Monthly

Yachting Monthly

Is Your Diesel Bugging You?

One of the problems facing leisure yachtsmen is diesel fuel quality. While your supplier might still be sourcing 'good old-fashioned sulphur-laden diesel' it may not be long until modern 'ecologically friendly bio-diesel' will replace it. I use both terms with a pinch of salt, but the implications of the change cannot be dismissed. The demon we are up against is the humble diesel bug, whose presence and effluent can result in sludgy deposits in our tanks all ready to be stirred up in a rough seaway to block our filters and stop our engines at the most inconvenient moment.

Non bio-diesel is far less hygroscopic (water absorbing) than the modern FAME (Fatty Acid Methyl Ester) con-taining biodiesel now sold at the majority of marine diesel pumps. While fuel producers have taken steps to ensure that the diesel should be in good condition when put in the supplier's tanks, the problems start once the fuel is dispensed into our own tanks. Basically, the potential issues depend on how quickly the fuel is used. For motorists and commercial users who replenish their tanks regularly there is little risk. For those of us who do not use a tank of fuel every 6 weeks the risk of diesel bug infestation in the water/diesel interface rises rapidly.

 

Is Your Diesel Bugging You?

 

In my own case, my BUKH 36 only sips at the 260 litres of diesel in my tank. This capacity is handy if I needed to motor 24 hours a day for 5 days, but in normal circumstances I only use half a tank every season. This leaves the remaining fuel to sit unused over the winter while the FAME attracts moisture, allowing organisms - diesel bug - to grow. Add the problem of condensation, and water collects in the bottom of the tank providing the fuel bugs with all the sustenance they need for an orgy of proliferation and filter blockage.

The solutions? We know that keeping the tank full helps eliminate condensation. Rapid diesel use may help in the summer, but how about the winter? Buying from a reputable source and checking what type of fuel you purchase is wise. Protective additives and biocides are also essential to both kill the diesel bug and limit chemical breakdown of the fuel.

Aside from these tactics, the most reliable way to keep your diesel fresh and clean is to fit a fuel polishing sys-tem. All this really consists of is a 30 micron superfilter inserted into the fuel line in advance of your existing primary filter. A pair of shut-off valves allow fuel that has passed through the superfilter to be pumped back into the diesel return line and thence to the tank. A timer can be set to operate the pump and filter system for 2 hours per week - this is enough to circulate the diesel in your tank, keeping it fresh and extracting the water and any diesel bug growth. When running the engine, just alter the valve positions and all the benefits of the superfilter are passed straight to the fuel entering the engine.


My solution - Fuel Guard’s FDG1120

The system I chose is made by Ian Currie of Fuel-Guard, and is centred on their FDG100 with its specially coated 30 micron stainless steel filter element and water separator. With the optional Water Sensor this is coded the FGD1120, and the kit is completed by a pump with a collection of fuel hose, stop valves, T pieces and connectors. All I needed to add was my choice of electronic timer and a couple of connector adaptors and hose barbs to suit my rather ancient fittings.

FGD1120


Fitting the FDG1120

With a little planning and forethought, the actual installation was child's play. My first step was to use my adaptors (8mm CAV) to connect the FGD1120 via a T-piece and stop valves to the existing primary filter on the forward engine bulkhead. I ended up cutting the copper inlet fuel pipe to insert a flexible hose, and screwed the whole to the bulkhead. The 'polishing arm' of the T-piece was connected by the supplied fuel hose to the pump screwed to the side bulkhead, and this polishing return was fed into the fuel return line via another T-piece and stop valves. My fuel return line is a type of plastic, and, once I had the correct size hose barbs, it was a simple matter to cut the pipe and clamp it up.

Fitting the FDG1120

 

Fitting the FDG1120

 

The next step was the electrical supply for the pump, timer, and Water Sensor unit. The Water Sensor alarm unit mounted neatly on the other side of the engine bulkhead, us-ing existing holes. It has a green 'OK' LED and a red warning one backed up by a buzzer. I connected the timer and power supply to the house 'bypass' fuses alongside the bilge pump supply - this system preserves the gas, bilge, and now fuel polishing system supplies even if the house battery isolator is turned off. I set the timer to turn on for 2 hours at 2pm every Wednesday, and turned on the manual over-ride to test the system. A reassuring buzz from the pump and splash of the returning fuel confirmed all was well.

 

 

I do have to remember to turn off the timer and turn the stop cocks to 'Engine' when I arrive on the boat - and similarly, on leaving the timer is activated and the stop valves set to 'Polish'. My fuel is currently clean, thus so far I have not been concerned by dirty diesel. I am, however, reassured that any water or debris that gained access to the tank will be regularly polished out. How often the filter will need to be cleaned re-mains to be seen - it is washable - and any separated water can just be drained away at the bottom of the filter.

On Fuel-Guard's website Ian Currie stars in a video which finishes with him quaffing back wa-ter that the FDG100 has separated from the fuel. I have no plans to emulate him - I'll stick with a pint of good old pale ale.

Fitting the FDG1120

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