Re: Paranoia about the D3-110 Volvo Penta - diesel bug

Matt Salatino

There are only two ways to keep your fuel tank, when you store a boat:
1) completely full, to the top
2) bone dry, empty.
Chapter 1:
The reason is that during the course of the day, air expands and contracts. If there is an air space in your fuel tank, air is constantly flowing into and out of the tank through the vent line, due to the normal expansion and contraction of air as the temperature rises and falls during the course of the day. The problem is that the fuel, a liquid, with a much higher specific heat (capacity to hold heat)remains at a more constant temperature. This heat sink of the fuel in the tank causes much of the water vapor in the air, to condense to liquid water in the tank. Only a little bit every day. A few months of this activity in a relatively humid (sea air) environment can produce a significant amount of liquid water, that settles to the bottom of your tank.
Chapter 2:
Diesel bug is an algae that has developed the ability to survive by eating diesel fuel, and using the water at the fuel water interface to get oxygen. So the bug lives, reproduces and dies in that fuel/water interface, producing the black gooey sludge.
Having a partially empty tank exacerbates this problem.

Storing your boat with completely full tanks eliminates the air space, so moist air does not get in and can’t condense its moisture in the fuel. An empty tank (difficult to do) doesn’t provide the heat sink to cause the water to condense so fast. It will to some extent, but not so rapidly.

We’ve experienced this first hand. After cleaning our tank we were bug free for about 5 years, traveling through The Caribbean, storing the boat every hurricane season in the tropics. One season, we forgot to fill the tank, and had diesel bug the next cruising season.
I also think using Biobor or equivalent, is a good thing.


On Feb 9, 2020, at 9:28 AM, Scott SV Tengah <Scott.nguyen@...> wrote:

My paranoia about my Volvo D3-110 (rev c) has been kicked back into high gear. I think this applies to anyone with a diesel engine but particularly with the hyper sensitive D3-110.

I know a few A54 owners with failed D3-110 due to water ingress. We've discussed that on another thread. I'll leave that discussion there.

Recently I met a HR46 owner who had to lag behind the World ARC ($$$$!) because of diesel bug issues on his D3-110C. Another HR48 owner had the same issue and in both cases, the engine died and wouldn't start back up. His tank was disgusting, apparently. I've opened my inspection hatches and my tank is nearly pristine. But I am not going to rest on my laurels. 

What do you guys do to keep your fuel system clean? Here's my procedure and I hope I can improve on it with your help:

1) Diesel only from places that get high turnover. We aim for duty-free, so they're usually in high demand.
2) Outside of the US and EU, we use the Baja filter. Damn slow at only around 8liters per minute, but you gotta do what you gotta do... That said, I know of a few owners in the EU who have had diesel bug - seems more prevalent with biodiesel.

One idea to reduce filling time (900/8 = nearly two hours!!) is to use the Baja Filter to fill up our spare 20liter jerry can and then inspect the Baja filter. If all is good, just fill up the boat without the filter.

3) I use BioBor JF. I don't know if it's the best, but I found a bottle in the US that was enough to treat 10,000 liters, so that was my decision making criteria.
4) I have 10 micron Racor filters in the water separator filters. I carry 15 filters aboard.  Two micron in the Volvo, per spec.
5) Pray.

What do you all do to ensure you aren't stricken by the bug?

2007 A54 #69
SV Tengah

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