The dreaded diesel bug.

"Diesel bug, also known as fuel bug, is a term for microbial contamination of diesel fuel, primarily caused by the growth of bacteria, fungi, and other microorganisms in the presence of water. This contamination can lead to blocked filters, corroded fuel lines, and even engine failure."

Google AI description.

The bug is becoming more prevalent as they love bio-diesel and is a particular problem in boats due to condensation and for many low usage. If the strands, alive or dead, get sucked into the pick up pipe they will quickly block the filters and stop the engine and that most often happens in rough seas when you least want it.

Fuel Treatments:

Have two purposes, to kill the bug and to disperse it into very fine particles that will pass through the filters and injectors to be burnt in the engine. Good ones will also reduce water in the fuel that the bugs need. Most treatments do both and if used in a high "killer" dose will kill most, but not all, quickly. The treatment I use is one of the best all rounders although it doesn't kill quite as quickly as some. I chose it largely because it is the go-to treatment for the fishermen of Newlyn. To be on the safe side I always use the "killing" dose as soon as the fuel goes into the can and often before, as in the great scheme of things, its not that expensive and you can't overdose.

Coming round from Fishguard to Dale I got it. My Facebook post: 

Diesel Bug! 🤬🤬🤬🤬🤬🤬🤬 Earlier I decanted some diesel into the tank and in the can were the remains of diesel bug. Hopefully dead as I always put a double dose of Fuelset in with it. I haven’t had any red diesel in it since Kirkwall and only once before at Howth outbound, so unless it has been lurking there since and I have not seen it then it has come from a roadside fuel station. 

It’s a yellow plastic can [that was new this year] and the crud was easily visible so I don’t think it’s been there that long.

I have put a precautionary massive dose of Fuelset into the tank (you can’t overdose) but I am going to have to get 40+ litres of fuel out of the tank, open it up and clean the whole system which will be a big and very awkward job but at least it is possible with the new stainless tank, unlike the previous bladder tank, and I’m close to base and not 500 miles away.

Whilst anchored at Dale waiting to go into the marina I first checked a second can that was filled at the same time, it was clean. It is a bit of a mystery because the infected can has never been empty for long and it has been cycled fairly frequently and has always had a big does of treatment, so I don't know why it grew in the can and I would have thought fuel pumps would filter out at least the large particles. 

I decided it would be a good idea to change the preliminary filter. Facebook post:

I didn’t want to risk the engine conking out going back to the marina so I changed the preliminary filter, not my favourite job as the seal on the Delhi filter is not easy to get in place and it needs a lot of pumping to bleed the system.

Previously I have always thought I had wasted my time [and money] as the filters were always clean. Not this time. The filter was replaced before this cruise so I’m in for some work cleaning the whole system:

The filter opened up, I have never before seen anything other
than the odd spot.

And in the water trap, previously that has always been clean.

This would suggest that some seriously contaminated fuel was introduced earlier this year, the prime suspects would be red diesel from Howth or Kirkwall where turnover would be less than the service stations I have used this year (Milford Haven, Tobermory, Stromness, Stornoway, Tobermory a second time and Ardglass).

The next steps will be to test the fuel to make sure it is all dead and then to open up the tank for inspection and cleaning which is going to be a sod of a job.

To be continued.