Diesel Bug - What It Is and How to Fix
Introduction
Coming back one afternoon from Elliot key to Coconut Grove with an unusually choppy bay, the starboard engine of our Fountain Pajot Lucia 40 “Andares” stalled. With a lee shore to our starboard, a strong wind blowing from the port side, and the running engine being the port one, it was not possible to steer the boat away from the shallows. We had to anchor and wait to be towed home (Thank you Boat US). Back at our mooring ball in Dinner Key Marina, it was troubleshooting time. Hey, if it didn’t breakdown now and then, it would not be a boat!.
And this was, ladies and gentlemen, how I became aware of Diesel Bug. The fuel line entering the starboard primary fuel filter had an about three inches long blockage of a thick, dark brown goo, that I was to find out was diesel bug. The picture shows the upper face of the filter, where the blocked fuel line had dumped the goo on its way to become completely blocked by it.
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A check on the port side engine revealed that, although not as bad as the engine on the other side, it was on its way to a similar breakdown soon.
What is Diesel Bug?
Like often happens in boat life, I quickly transformed from a complete ignorant of this issue, to a expert of sorts by intensively researching the subject matter. Tons of literature can be found on the web, and I like to summarize the phenomenon as microbial contamination that occurs in diesel storage tanks and fuel lines. The presence of water in the fuel provides for the perfect environment for the growth of diesel bug.
How to Fix Diesel Bug
ixing the immediate problem (getting the engine running) is easy, just remove all the goo blocking the fuel lines from the tank to the engine, and change the fuel filters.
How to Prevent Diesel Bug
The first line of defense against diesel bug is to minimize the amount of water in the diesel tanks, including:
- Keeping the tanks full to reduce water condensation in the tanks
- Regularly drain water from the tanks
- Use fuel additives. They come in two types, treatments that attack the water condensation in tanks, and biocides that attack the microbial growth itself.
- Fuel polishing
What is Fuel Polishing?
Fuel polishing consists in cycling the content of a fuel tank, pumping the fuel from the tank, running through a fine filtration system and returning the fuel to the tank. This fine filtration will remove water and any impurities from the diesel (Yes, including diesel bug!).
Building a Fuel Polishing System
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A simple polishing system consists of a Racor type filter, a fuel pump and a way of providing power to the pump. The picture shows the working prototype we build for “Andares”. The prototype worked fine, we will be building a permanent system, and intent to running it every six months to start with, the observed results will indicate whether this period should be reduced or extended.
I stated we used a “Racor type” filter instead of as Racor, because of pricing. The knock-off version we bought in Amazon cost less than $65 dollars, a fraction of a similar Racor one. The fuel transfer pump cost less than $52 dollars. The system is rated at 120 gal per hour. Our diesel tank holds 80 gal. Assuming the actual rate of the system is 100 gph, we can recirculate the tank content when full in about 45 minutes. I used hoses and wires we had around the boat, but even if buying these the overall cost should be around $ 150. This is money well spentThe picture shows the filter capturing the diesel bug as it circulates the fuel.
The picture shows the filter capturing the diesel bug as it circulates the fuel.
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