Tuesday, May 5, 2015

Diesel Bug

This is a project post.

When I first left Seattle, in 2011, I had a new diesel tank, with two inspection ports and everything was shiny clean.  After my first year of traveling through California to Mexico, Hawaii and back to Seattle I ended up without any diesel problems, everything was still clean.

After leaving again in 2013 and heading down the California coast, again, to Mexico and then to the South Pacific, somewhere along the way I picked up a bad load of fuel, or a series of bad loads of fuel and my diesel tank ended up contaminated with the dreaded diesel bug.

I had no idea what 'diesel bug' was, or what to expect when I had it.  I've learned a little since then.

While in New Zealand, one of my chores I had on my boat project list was to inspect my diesel tank.  I had been noticing that the diesel I could see in my Racor filter was more opaque than usual, but it just seemed like it might be a different type of dye being used.  I couldn't see through the glass bowl of my Racor the diesel was so opaque.  (oh, for non-sailors, a Racor filter is a fuel-water separator along with a filter that is the first line of defense getting clean diesel into the engine.  There is a secondary filter closer to the engine which removes smaller particles than my Racor filter does.)

When I opened my diesel tank and shone a flashlight into the tank, my strongest flashlight couldn't penetrate the diesel to see any of the aluminum walls - it was clearly more opaque than I had thought.  There is a chandlery close by in Opua, Cater Marine which has a little display of some fuel additives. One of the displays has two glass jars, one with the fuel contaminated and one with the additive.  The interesting thing is that the contaminated sample looked a lot like my diesel - opaque, and in my case, reddish diesel.  There was also a brochure showing the same before/after comparison of a different additive - again, diesel being so opaque you can't see through it being bad.

Now I knew what contaminated fuel looked like, and knew that I had it, and I was standing in front of a display which advertised a product that you add to the bad fuel and over time it becomes good again!  Yay I thought to myself, how easy is that!

So I bought some, added it to my tank and waited a day.  After a day I started feeling like an idiot and doing more web 'research.'  After speaking with a few experts, it turns out that the best thing to do is to remove the bad diesel, clean the tank and lines and start again with fresh fuel.  This seems entirely obvious in hindsight, but its a somewhat ugly job and I was hoping for an easy shortcut.  Alas, it was not to be.

It turns out that the additive might kill the bug, but it remains in the tank.  The diesel bug is mostly water - its a bacteria and the bacteria is mostly water - and that it would end up possibly clogging my filters or going through my injectors as bacteria is tiny.  Sending stray amounts of water through a diesel injector is not good.  One of the things that a diesel engine likes is clean diesel fuel, burning through 1/2 a tank of bad, dead, diesel bug seemed a little reckless and possibly expensive if the high pressure pump or an injector was damaged.  Although, having said that, my engine seemed to be running just fine for all the time leading up to my cleaning the bad fuel out.  The Racor filter was obviously in need of replacing when I saw it.

Anyway, I ended up removing the diesel fuel, cleaning the tank until it was spotless, adding some clean diesel, running the pump on my engine to circulate it through the filters and lines, replaced both filters, removed the tainted fuel and called it good.  Its good to know there is clean diesel in my tank again - if I'm good to my diesel engine I'm hoping that it will be good to me in return.

During the latter part of this cruise when I started meeting people who had been cruising in different parts of the world I stated hearing their opinions on how to add fuel to the tank.  In America and Mexico the fuel seemed clean, it didn't seem to be an issue.  Cruisers I had met who were finishing up a circumnavigation had been through this process and had learned their lesson.  The general consensus is that if you don't filter the fuel going into your tank, you will get diesel bug eventually.  Its just a matter of time.  The people I met who were filtering their fuel didn't have the diesel bug problem, and most of them have pretty strong opinions on needing to filter the fuel.

The first time I left Seattle, I actually had the West Marine fuel filter on board, which seems to be very common and entirely adequate.  I bought it at the last minute and threw it in without ever trying it.  Along the way I had brain freeze when I tried to think of how to use it.  A Pacific Seacraft has high bulwarks, so the caprail is three or four inches off of the desk.  The fuel inlet is close to the caprail, which interfers with the filter.  I couldn't figure out how to use the filter and ended up giving it away in Mexico.
It doesn't fit!  Impossible!
After realizing I had diesel bug and that I needed to clean my tank and replace my fuel I started thinking again about the filter issue - and almost immediately came up with the obvious solution.  I feel like an idiot offering this to others as a solution, as its entirely obvious.  Anyway, I bought a short length of hose, a hose clamp and fashioned a way to fasten the filter to a stanchion and now it works perfectly:

Yeah, I know.  Its an amazing solution, right?

To add the fastening loop, I created a loop of 'small stuff', twine, in my case a thin dyneema.  I punched a pair of holes in opposite sides of the filter just below the top lip and whipped the dyneema loop to the filter using seine twine.  I then added a bungee and hook which I attached with a couple of hog rings.  It seems to work.

To use it, rig it up as shown, and then add fuel.  Its pretty easy.  If the fuel contains water, which the diesel bug needs to live, the water is caught by this filter and doesn't go into the tank.  It also stops bits of debris, which seems like a good idea.  

Its the water that is important for diesel bug to live, this filter stops water going into the tank.  There is a caveat though.  I used to add an additive to the diesel after buying it, so treated diesel sat in my diesel jugs.  It turns out that some additives will cause water to break up into small particles, rather than pooling together.  If you add one of these additives to the fuel before pouring it though the fuel//water filter, then the water will pass through - so I've stopped treating the diesel before it goes into the main tank.

After using the filter, you end up with some diesel at its bottom that is just stuck, it pools at the bottom.  I'm finding that one large fuel diaper, cut into 1/4's cleans it all up.  I use two of the quarters cleaning the diesel out, then one to clean the filter up, and one more to clean whatever else.  It all fits into an extra-large ziploc and stows forward in my chain locker.

I'm posting this in the hope that there is a sailor, somewhere, who might be able to avoid contaminated fuel and having to clean their tank out as a result.


I'm hoping to leave NZ bound for Tonga in a few more days.  This will be my last post until I'm underway.  As usual, if my blog posts stop while I'm on passage, nobody should panic, electronics are sensitive and a saltwater passage is a harsh environment.


  1. Great information! Good tip about the fuel additive. Nice for me that you have the exact same boat! I'll go get me some hose and clamps for our fuel filter.
    By the way, your brightwork looks great. When did you refinish it last?
    Have a great trip to Tonga.
    Fair winds

    1. My varnish is in pretty good shape right now - I added two coats a few months ago. I was hoping to get one more coat on before leaving NZ, but that hasn't happened. I don't know why, but the last time I was in the tropics for some reason I had it in my head that I couldn't add a coat of varnish while I was there - I 'needed' to wait until I got to NZ. This time I have more varnish aboard and will add a coat when its needed, in a few months. I still like how the varnish looks and really like how well it protects the wood, but I'm starting to see the attraction of lower maintenance approaches...