Fuel tank – cleaning

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This topic contains 9 replies, has 6 voices, and was last updated by  Steve Ehrler 8 months, 3 weeks ago.

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  • #8589

    Since we started cruising full-time in 2015, we have burned more than 2500 gallons of diesel fuel. In that time, we have never plugged a fuel filter. Nevertheless, I periodically remove large gobs of biological contamination from the housing of our Racor 460 fuel/water separators when changing the primary spin-on filter cartridge.

    To facilitate tank cleaning now and in the future, I intend to install one (or more) Seabuilt clean out/inspection ports and I need to know how the tank baffles are designed so I know whether to install one or more ports.

    Has anyone been down this road already, or should I just call Mirage?

  • #8590

    Henry Dennig

    Gene had photos of Lo Que Se A during construction that he left for John Savage on Colorado Cowboy. He thinks one of the photos showed the baffles.

  • #8591

    Joe Pica

    Dick, I shared a link to a dropbox picture of when CA was under construction. If you can not see it I’ll e-mail the ;picture to you. Looks to be 7 separate chambers/sections so you would need to cut alot! Perhaps a professional fuel polisher/chemical cleaning solution/polisher to dissolve everything and filter it out. First they remove the fuel, then introduce a wand that can be thread into the chambers via the mouse hole corners cutouts. Not easy but should be doable. If you take on soy diesel it will dissolve any asphaltines …but you will go through many many filters. I’d call Ken.

  • #8592

    Thanks, Joe. I got the picture in Dropbox. Great info. It appears there are six baffles running laterally inside the fuel tank. If I install the inspection / cleaning port on the back of the tank in the engine room, I should get a pretty good idea of what I are dealing with. With luck, the crud has gravitated through the gaps between compartments and is concentrated in the lowest rear compartment, where I can suck it out via the port. But if the gunk is widely distributed and mostly inaccessible, I should still be able to shock the system with Biobor JF to kill it. That would break down the gelatinous globs. The resulting crud could then be agitated into suspension so it flows more readily to the lowest part of the tank. With an access port the clean out is simplified. But I would think my fuel polisher could do the job, too. I’ll do as you suggest and give Ken a call to get his thoughts.

    Thanks again for the help!

  • #8631


    Is this a common problem with these 7 or 10 year old fuel tanks?

    I was going to ask about fuel getting stirred up in bumpy seas and causing issues if fuel is polished compared to those trawlers who do not have the fuel polishing setup?

    Thank You

  • #8632


    Here is a excerpts of my conversation with the factory:

    Since we started cruising full-time in 2015, we have burned more than 2500 gallons of diesel fuel. In that time, we have never plugged a fuel filter. Nevertheless, I periodically remove large gobs of biological contamination from the housing of our Racor 460 fuel/water separators when changing the primary spin-on filter cartridge.

    To facilitate tank cleaning now and in the future, I am thinking about installing a Seabuilt inspection / clean out port (or ports).

    Joe Pica sent me the attached picture of the tanks being glassed over. It looks like there are six baffles in the fuel tank. Based on your knowledge of how the baffles are designed, where should the port (or ports) be placed to facilitate clean out?

    [Ken Fickett]
    My opinion is that you are creating way more problems then you are solving. I have always had the attitude that “if it ain’t broke don’t fix it”.
    I do not believe you can find a GH owner that has ever had a fuel issue that required “cleaning” the tanks. Having had to repair tanks that were damaged we always found them pretty well spotless. Also, please do not let anyone convince you that the fuel pickups should not go to the bottom of the tanks. They should and all contamination should be removed by your filters. When that is not the case you do in fact develop sludge on the bottom of the tank and you will need large clean out ports. Does your boat have a fuel polisher system?

    I’ve had biological growth in the tanks since the we bought Avocet from Steve and Marilyn. I took the conservative route and expected that over the course of two years, 10,000 miles and 2500 gallons of diesel, the filters and the fuel polisher would do their thing. That should have worked. But it didn’t. The crud is still there. Nobody has touched the manifold or the pickup tubes. So, if it’s not too much trouble, could you answer my question about the baffle design?

    [Ken Fickett]
    There is not only a mouse hole on center line but additional mouse holes at the midpoint of both right and left halves of the baffles and chine corner. I think it would be exceedingly difficult to fish a pressure hose to the forward side of the tank which is why when we install a standard fuel polishing system we do that with a 1 inch diameter filament wound high pressure fiberglass pipe that extends to the forward most end of the tank and then makes a 180 degree bend to orient flow aft. That pipe is contained inside the tank. Our fuel polishing pump is a relatively high pressure high volume pump to facilitate “washing ” the tank. I would think that removal of the existing port would provide adequate cleaning of the tank. Any other ports would need to be through the cabin sole since the flooring is directly on top of the fuel tank. The inside of the tank is finished in a very slick gelcoated finish which tends to keep the surface of the tank very clean. Hopefully that gives you an adequate description of what you are dealing with.

    Ken, this description is exactly what I was looking for. Thank you.

    My plan is to shock the fuel tank with Biobor JF and then run for an hour or so in some agitated water so it gets thoroughly mixed. Then find a nice anchorage and run the fuel polisher for 6 hours. Run again on Day 2 and polish a second time. Then monitor things. If it’s still contaminated come this fall, then I’ll probably remove the existing manifold to inspect and clean out – figuring most (if not all) of the gunk will be right there at the lowest point in the tank.

    [End of exchange]

    Here is an excellent article on the subject of fuel polishing that discusses fuel tank contamination and what to do about it:


    N37 Avocet

  • #8638


    Thank you for this reply and link.
    Off to check out the article

  • #8639

    You’re welcome, Jim.

    Avocet, N37-08

  • #8757

    John Reynolds

    From John Reynolds, Former owner of Easy, now M/V Balena

    We had our fuel tanks cleaned in July 2014. The fuel filters were continually clogging with stuff that looked like black snot. We went through six primary fuel filters making the trip from Hampton Roads to Baltimore.

    A copy of the quote from CleanFuels is attached.

    Removing the fuel tank level indicator assemblies provided adequate access to clean the tanks. They used a PVC wand, 1/2″ CPVC pipe I think, inserted into the tank through the hole in each tank. They were able to get the wand through the baffles all the way to the forward end of each tank. There was a “lot” of water in the starboard outboard tank, laying in the inboard aft end of the tank. For some reason, the pick-up for the fuel transfer pump did not pick up the water. I think the water was due to condensation on the inside of the tank when cruising in cold water, which we did. They also recovered a lot of the black snot from both tanks.

    After returning to our slip, the guy on the next boat said that he ran a fuel dock for a number of years. He asked what type of fuel conditioner did I use, to which I replied “none”, but that I always used VALVTECT treated diesel fuel. He recommended using Star Tron and Biobor JF each time we fill a tank, and said that VALVTECT is a waste of money.

    I followed his recommendations and had no further problems. However, we only cruised for another year before becoming dirt dwellers once again.

    Appologize for the late reply but I just saw this post.

    You must be logged in to view attached files.
  • #8759

    Steve Ehrler

    John –
    I just changed the Racor fuel filters and saw some of the “black snot” you referred to – a little on the port side and quite a bit more on the starboard. In compiling maintenance requirements (yes, still trying to wrap my head around how to not forget to do things), I had noted the recommendation to add Star Tron and Biobor JF. Since we had refueled, I oredered some and then added it. Otherwise, have not had a problem with the fuel filters (Thank you John !)

    Seve & Jan

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