Tiger79, thanks for the reply.
My concern about fuel polishing is that it does not get the grunge off the tank any better as it does not, by itself loosen the grunge. I've also found that on the two occasions I have had diesel bug sufficient to stop the engine, the primary filter was not the cause of the blockage. A lump of gunk the size of a raisin was caught in the fuel cut off valve in both occasions. I believe this is the cause of blockage in most Bavarias and also other makes that have a small aperture in the fuel cut-off valve.
If the Volvo Penta diesel engines have a return of fuel of 40 times, similar to what I think the Yanmar Diesels have ( I may be corrected on these figures) then running my D1-30 for 2 hours would circulate 80 litres of fuel through my filters. I don't think the decolourisation of the fuel is the problem, the lumpy bits in the tank are the real problem if they break off as a lump.
I have fitted a clear plastic strainer in the fuel line between the tank and the fuel cut-off valve. It collects the lumpy bits. I have also observed that the lumpy bits in the strainer are broken down by Startron, an enzyme treatment into particles that do appear to go through the primary filter and possibly, as advertised, are then burnt through the injectors. The Startron does not appear to work as well when the boat lays idle in winter for any length of time. I have had Startron in my fuel for the last 4 years. I have a sneaking suspicion that it only works when the engine is used. I think the Startron may have contributed to the breaking of of the gunge in the tank as both attacks occurred in the first trip of the season in sloppy conditions under motor.
I am trying to determine whether Startron works best whilst the engine is running, either because it requires circulation of the fuel to mix it or possibly needs a bit of heat from the returned fuel to the tank.
The Volvo mechanic and also the Bavaria agent in Malta both swear by the clear plastic strainer being fitted to the fuel line. Many boats in Malta do not use biocides or enzyme treatments. They do not clean their tanks, accept Diesel Bug as a part of life and merely collect the grunge in the strainer which they replace once a year if it becomes close to clogging. They also claim that in most cases, if a strainer is not fitted, it is the fuel cut-off valve that will block, not the filters or lines.
Fuel polishing moves a lot of fuel around but does not heat the returned fuel and does not clean the sides of the tank.
I have spoken to numerous "Yachties" that have had diesel bug over the years and many have had re-occurrences, no matter what additive they have been using. Many of the older British makes of boats do not appear to have blockages in their fuel lines or fuel cut-off valves but in their primary filters. I suspect that this is because they may have larger diameter fuel lines allowing the lumps to reach their primary filters where it is caught. There is also a thought that the FAME added to diesel in Europe may be adding to the problem as it attracts a greater range of "bugs" and may also be partially "Clouding" the fuel in low temperatures found when yachts are kept ashore during winter.
Tiger79, did your old boat have a small aperture fuel cut-off valve. Do you know where the blockage actually was? "Yachting Monthly" has published a number of articles in recent years regarding the use of Biocides and Enzymes and rated them under laboratory conditions. Each treatment they reported upon had positives and negatives. None appear to work in all conditions.
I'm looking for a solution that involves minimising the risk through additives, keeping tank full in winter, ensuring water can't enter through the fuel filler pipe but also being able to stop the blockage when this does not work.
Any further thoughts or information would be appreciated.
Regards
Craig
"Shirley Valentine".
