Peter Franklin
Wednesday, 23 August 2017

A tank of worms!

Last winter I did the same thing that I (and many others) have always done, and filled my boat’s fuel tanks to the top with 400 litres of diesel before winterising the boat in November.   

In the spring, I also did what I always do and opened the ball valve at the bottom of the fuel tank, intending to drain off a few litres until clear/clean diesel came out. But this time, I was horrified to see that brown curly worms were coming from the bottom of the tank, and after a minute or so, the ball valve clogged solid and no more diesel would flow out!

Having read all about the increase in diesel bug problems in recent years, I decided it was a job for experts. So I contacted the company Mobiele Tank Cleaning, run by Kees Kingma and his wife Elly Strik.  

They did a great job of emptying and cleaning the tank, recycling the entire contents through multiple filters, and put it all back in the tank treated with a ’shock dose’ of biocide additive. They also had to cut a hole in the tank top for access, and fitted it with a bolted hatch for easier inspection and cleaning in future.

Since then, we have cruised the entire summer without any problems on the Yanmar engine, which I am sure would not have been the case if we had left the contamination in the tank!

Anyway, in talking to Kees and Elly, I discovered that they had really developed a lot of expertise about diesel contamination, based on practical experience and real-life testing on their own boats, combined with a lot of detailed research. Much of this they have written about in advisory documents (in Dutch), and they have agreed to let me share some of it here on the METSTRADE Community.

Diesel fuel changes to improve the environment 
In the European Union, the standards for composition of fuel and emissions are increasingly being tightened for all vehicles. Since 1 January2015, a new standard named Euro 6 was applied, and this specified maximum amounts for emission levels from vehicles. The current diesel is the ULSD type Ultra-low-sulfur (sulfur) diesel with the code EN590. This standard prescribes the composition of the fuel, and it necessitates that a 3.5% to 7% of biofuels (Fame) must be added.

These changes are obviously intended to reduce the environmental impact, and at the same time, to create the perfect fuel for all vehicles and engines that have a fast turnaround, such as trucks, industrial engines and the current diesel cars. Also this ULSD diesel is necessary for the currently used common-rail diesel engines.

The problems for boat engines and their fuel storage conditions
This new ULSD diesel fuel is clearly formulated differently to the blends we were all used to several years ago, and unfortunately, for the typical boat owner, it does come with some problems. This essentially manifests itself as water, mould and bacteria growth in the tank, becoming much more commonly found.

Apparently a large percentage of the call-outs by the leisure marine breakdown service (KNRM) in the Netherlands, finds that the engine failure is due to blockage of the injectors by these contaminants, which cannot be dealt with by the inline filters.  

“It is therefore necessary to give more attention than ever to the control of the boat’s diesel tank, says Kees Kingma of Mobiele Tank Cleaning.

How to prevent or minimise these problems?
One way is to always obtain your fuel at a large gas station where refueling is done in higher volumes. You can also do this along the road in a car pumping station with jerry cans and a siphon to prevent spillage.

 If you leave the boat unused for a longer period, such as over the winter, it is better to leave the tank empty! Kees says, “the old mantra of ‘the tank should be full’ is still stubbornly observed by many, who think that this will work to prevent condensation and bacteria growth.” But, he says that the current (bio) diesel is only good for storage over a few months, and not a few years as the previous formulations were. This means that the smallest amount of water in the tank will quickly encourage bacteria growth, and become a problem in the tank and motor, and this is especially a risk for the injection pump.

A word of advice from Kees Kingma: “Personally, I empty the fuel tanks of my boat every autumn and make them clean and free of solids. After that, I put in a few litres of gasoline. I do this because gasoline evaporates in case of frost, and also ensures that tanks only breath to the outside. This prevents water from entering the tanks. I also partially close the tank ventilation with a self-assembled tap. In the spring, I drain out the gasoline from the tank, and then fill it with fresh diesel.

Oh, and do make sure to use a good quality fuel conditioning additive in your tank. Kees recomends a product called Bardahl - More info here:


Kees concludes, “Since I have done this over several years, I have no water or contamination in my fuel tanks!”

This is a personal story, with advice from experts,not from me! It is also translated from Dutch, so I hope that it is as accurate as possible.

Do you have any experiences (similar or not) with diesel fuel, that you would like to share with the Community?

Is this just another step towards the eventual replacement of internal combustion engines in leisure boats, and hastening the coming of more electric propulsion concepts?

What do you think? Please do leave us your comments below.

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