jcpa
Member
It was fine on a long passage under motor one week, but next week the engine just wouldn’t rev properly. Speed through the water was down from 5-6 knots to about 3 knots, and progress against the tide was virtually impossible! Can anyone help me sort this out? The checks I’ve done seem to suggest Diesel bug is the main culprit, with sediment build up probably blocking the entrance to a fuel hose. I have cleaned everything reasonably well, but should I fit a pre-filter between the fuel tank and the fuel hose?
My checks started at the primary filter/water separator in the engine room - two metres of hose (with numerous bends to pass through cupboards/lockers/etc) away from the fuel tank that sits under the chart table. The filter seemed not too bad – not obviously clogged, but with some gloop hanging under about a quarter of the base of the filter element. The secondary filter (between lift and high pressure pumps) was totally clear. I anyway replaced both filter elements, but the engine still wouldn’t go above about half speed. On rechecking the primary element, there was no evidence of contamination/blockage, so I had the injectors out and professionally checked (they were fine).
So then I drained the fuel from the tank – down to the level of the supply tap, about 25mm above the tank base. The fuel was a nice clear amber with no sediment, but a couple of rice-grain size dark oily lenses (note, I only use road diesel, about 30 litres a year, brought to the boat in a Jerry can to which I usually, but possibly not always, add Fuel-set at the recommended standard dosage).
However, in the tank base, just below the supply tap, a drain plug allows the final half-litre of fuel to be extracted. It was quite mucky with dark oily pieces of sediment – some quite dense and sticky. Presumably this indicates diesel bug.
By peering through the 25mm tapped hole in the tank top, and poking around with a brush on a long stick, I have managed to clean most of the black deposits from the tank sides – but some areas are inaccessible due to baffle plates.
Some club colleagues have said the tank must be spotlessly clean, others say it is sufficient to get the sediment level well below the supply tap, and avoid new sedimentation by using fuel treatment. Yet more say I should fit a pre-filter in the engine room to stop sediment reaching the primary filter - particularly if I use a biocide that turns any further bug to black sludge.
I agree that a pre-filter may protect the primary filter, but is the effort and cost justified – considering how cheap filter elements are. There is no obvious/suitable siting point in my engine room (more of a cubbyhole under the companion way), and anyway, I think any sediment would more likely clog either at the tank outlet (where a ½ inch BSP tap feeds a 4mm internal diameter hosetail into the fuel hose), or at a bend in the fuel hose to the primary filter (hose now replaced, but the old one didn’t seem to be clogged). If I need a pre-filter, it would seem best to fit it between the fuel tap and the hosetail, but it would need to be a small ‘inline’ filter – the tap is only only about 35mm off the sloping hull-side (approx 45 degrees).
Can anyone comment on this? Does anyone know of possible filters that might be suitable?
My checks started at the primary filter/water separator in the engine room - two metres of hose (with numerous bends to pass through cupboards/lockers/etc) away from the fuel tank that sits under the chart table. The filter seemed not too bad – not obviously clogged, but with some gloop hanging under about a quarter of the base of the filter element. The secondary filter (between lift and high pressure pumps) was totally clear. I anyway replaced both filter elements, but the engine still wouldn’t go above about half speed. On rechecking the primary element, there was no evidence of contamination/blockage, so I had the injectors out and professionally checked (they were fine).
So then I drained the fuel from the tank – down to the level of the supply tap, about 25mm above the tank base. The fuel was a nice clear amber with no sediment, but a couple of rice-grain size dark oily lenses (note, I only use road diesel, about 30 litres a year, brought to the boat in a Jerry can to which I usually, but possibly not always, add Fuel-set at the recommended standard dosage).
However, in the tank base, just below the supply tap, a drain plug allows the final half-litre of fuel to be extracted. It was quite mucky with dark oily pieces of sediment – some quite dense and sticky. Presumably this indicates diesel bug.
By peering through the 25mm tapped hole in the tank top, and poking around with a brush on a long stick, I have managed to clean most of the black deposits from the tank sides – but some areas are inaccessible due to baffle plates.
Some club colleagues have said the tank must be spotlessly clean, others say it is sufficient to get the sediment level well below the supply tap, and avoid new sedimentation by using fuel treatment. Yet more say I should fit a pre-filter in the engine room to stop sediment reaching the primary filter - particularly if I use a biocide that turns any further bug to black sludge.
I agree that a pre-filter may protect the primary filter, but is the effort and cost justified – considering how cheap filter elements are. There is no obvious/suitable siting point in my engine room (more of a cubbyhole under the companion way), and anyway, I think any sediment would more likely clog either at the tank outlet (where a ½ inch BSP tap feeds a 4mm internal diameter hosetail into the fuel hose), or at a bend in the fuel hose to the primary filter (hose now replaced, but the old one didn’t seem to be clogged). If I need a pre-filter, it would seem best to fit it between the fuel tap and the hosetail, but it would need to be a small ‘inline’ filter – the tap is only only about 35mm off the sloping hull-side (approx 45 degrees).
Can anyone comment on this? Does anyone know of possible filters that might be suitable?
