We have just had our second Diesel Bug attack in 2 years. Both attacks occurred while motoring in rough conditions with our tank less than 1/2 full and just after dozing the tank with an enzyme.
In both cases, the lump of Gunk did not reach the filter. In both cases the engine stopped because the gunk was caught in the fuel off/on switch.
The aperture of this valve is less than the fuel line. A piece of gunk the size of a raisin blocked the valve to such an extent it had to be blown out with compressed air. The fuel filter, in both cases had some Gunk but was not blocked to cause any drop in fuel flow.
We have now installed an inline fuel strainer before the off/on valve.
This strainer collects all the lumpy gunk that could block the off/on switch but allows small stuff through to the primary filter.
After installing the strainer a large blob of gunk was caught in the strainer. After 9 hours of motoring the enzyme in the fuel seems to have "dissolved" this gunk. The primary filter has some discolourisation but is clear. The fuel has been slightly discoloured by the gunk in suspension but the engine is performing well.
The Bavaria agent in Malta, as well as the Volvo dealer there have never had a problem with Diesel bug blocking fuel lines or filters after installing the strainer even though the strainer collects large blobs of gunk.
They have never seen a Bavaria stop because of gunk in filters and believe that all instances they come across the gunk is caught in the on/off valve.
I strongly recommend that everyone install a strainer ( 4 euro cost in Europe) in the fuel line before the off/on switch.
I also believe that the enzyme treatment actually loosened up the gunk in the tank causing the blockages we have had, but also later "dissolved" the gunk held in the strainer.
I have photos if anyone is interested and would appreciate feedback as I am considering writing an article on this issue.
This issue also affects other boats and is partly bought about by different regulations regarding the location of fuel on/off switches and the materials and fittings to be used in the construction of fuel lines. I am aware that the plastic see-through strainer I have installed is not compliant with the fire safety requirements but my risk analysis is that this is a minor threat compared to entering a harbor in adverse conditions with no engine.
Craig Hardy
s/v "Shirley Valentine"
2009 Bavaria 38
The Mediterranean