Fuel Tank Cleaning / Fuel Polishing: Recent Experience

Discussion in 'Main Morgan 38 Sailboat Forum' started by mpearson, May 13, 2019.

  1. mpearson

    mpearson Mark Pearson Staff Member

    Oct 18, 2012
    Home Port:
    Portland, OR
    Wow. I recently finished cleaning our fuel tank and polishing the fuel. I am very glad I did this - there was an alarming amount of sediment and poop (really!) in the tank.

    If you don't know if your tank has been cleaned recently, I’d highly recommend doing it. The following is probably “too much information” for a casual reader, but hopefully useful for someone considering doing this process.

    Caveat #1: If you have a gasoline fuel tank (probably not a Morgan 38), don’t do this! There is a lot more danger of explosion & you could blow yourself and your boat up. You’ll want to be very aware of sparks and grounding.

    Caveat #2: If you do this, be sure you know how to prime the fuel line to your engine. When you’re done, you will need to. It can be a little tricky. If you have a Perkins 4.108, I wrote a little cheat sheet many years ago here.

    I used a new-age trick that I think is a game changer: an inexpensive ($40) endoscopic camera. This is a pencil-sized camera with bright lights that I could move around in the tank as I was inspecting and cleaning. I could watch things from my big & bright iPad (or computer) screen.

    I don’t think the tank has ever been cleaned out. I know for certain that it hasn’t been in the last 15 years based on conversations with the most recent previous owner. But based on some of the things I found, I’d bet it has never been done in Zia’s 36 year life.

    I had (7 years ago) removed the fuel gauge and peered down into the inspection hole (1-1/2”diameter) with an intense light. All I could see was black. I chose to close it back up and act like everything was OK. I rationalized it was probably a black steel tank and that’s why it was so dark in there. Spoiler Alert: it's a fiberglass tank with a shiny white gel coat surface. It was so coated with sediment, goop and crap that it looked like a cosmic black hole from which not even light could escape.

    Our new Yanmar engine operates at very high pressures and I’d read a Nigel Caulder article about how filtration and clean fuel was even more important with these engines. Both my old Perkins manual and the new Yanmar manual recommend inspecting & cleaning the fuel tanks out annually. Yeah, right!

    A note about particle sizes and filtration: A micron is one-millionth of a meter. The largest particle that a human can see with the naked eye is around 40 microns in size. Oddly, I cannot find any “official” micron rating on our Yanmar filter, but I’ve been told by one dealer that it is 2 micron, and by another that it is 10 micron.

    I constructed a little polishing/cleaning rig from parts at Home Depot and Amazon.com. Total price was around $130. It polished the fuel in the tank to about 10 microns. In my opinion, that is very clean and ready for the Yanmar’s fuel filter.

    1- Endoscopic Camera with Lights
    2- 3/8” Copper Tube, Type L
    3- WiFi Router, came with camera, allows iPad to view video
    4- Pre-filter with Sight Glass
    5- Diesel Fuel Pump, 12V, 30 GPH
    6- R12T Fuel Filter w Water Separator
    7- 2X4 Wood Stand
    8- Fuel Hose, 3/8”
    9- 5 Gallon Diesel Jerry Can

    Perhaps more importantly: I cleaned the tank. We could easily polish the fuel to 10 microns but still have so much filth in our tank that wave action/bouncing could stir it all up, break it loose, etc. and plug our fuel filters. Precisely at a time when you don’t want a plugged filter & dead engine.

    Some fuel polishing companies use high throughput pumps & filters to blast things loose (in theory). I’m quite sure that some of the gunk and poop I removed would not have been removed with just stronger pumping. And certainly I wouldn’t have been able to see it visually without the endoscopic camera.

    I took the cheaper and slower approach and used a fuel pump that did 30 gallons/hour. I got a inexpensive Racor-like filter (hereinafter called R12T Fuel Filter) on Amazon.com with replaceable filters and a water trap. I hose clamped rags to the end of a copper pipe that was the intake, then I scrubbed and sucked it clean.

    It took a two days of work and I went through a whole bag of those white rags from Home Depot. I plugged and replaced the R12T filter twice, so I went through 3 of those filters. I took apart and cleaned the pre-filter in the sink with water probably 20 times.

    Here are the steps I took:
    1. I waited until the tank was less than 1/4 full. I only had 2 of the 5 gallon diesel jerry cans, and I reasoned that there should be about 10 gallons left. Note for the future: there was only about 6 gallons left when the gauge read 1/4 full.
    2. Removed the fuel gauge and started pumping through the filter and into the jerry cans. There was a huge amount of turbidity and very quickly the sight glass in the pre-filter was black and the bowl on the R12T Fuel Filter was black. This slowed flow down to a dribble.
    3. I decided I just wanted to get the fuel out of the tank and that I would use rags to mop out all the crap, rather than changing filters so frequently. So instead of moving the inlet around and stirring things up, I kept it quite stationary with the goal of only removing the fuel. It took about an hour to get the remaining 6 gallons out of the tank, and I stopped and cleaned the pre-filter about 10 times. In hindsight, my pre-filter was plugging even with the filter element taken out. Upon closer inspection, this was because the fuel needed to go through little holes that were about 1/16” diameter and many of the particles I was sucking out were bigger than that and plugging the holes. Also, I couldn’t find a rated throughput for this pre-filter, but I think 30 gallons/hr is unlikely.
    4. Then came the actual hard work. I cut the white rags into squares about 8 inches wide and hose clamped them to the end of the copper pipe. Using the endoscope, I scrubbed back and forth to clean the goop/sediment off the walls and bottom. See the "in action" video below. Repeated this a couple of dozen times. I added a gallon of my filtered diesel back when I needed more liquid to properly swab out the tank. When I started this step, the rags came out black with lots of sediment, metal shavings, slime, etc. They gradually got lighter and finally ended up being the pink color of the diesel. This took some time, but what the heck? It took 36 years for all this crap to build up so it seems reasonable that this step took 6 hours and a whole bag of rags to be clean again.
    5. I had to bend the copper tubing “up” a little bit when trying to push forward in the tank. The 3/8" copper tubing was Type L, which means it was fairly soft and could be bent to reach around corners or over humps. This would not have worked if it was rigid copper or a piece of dowel. There is a sump below the access port and where the fuel intake is located. See photo of the sump below. A straight probe would not be able to get over the edge of the sump, and into the forward portion of the tank. I was able to get about 36” forward of the access hole. That is also roughly the distance to the back of the mast, so I think I got the entire tank.
    6. During the swabbing of the tank I made a startling discovery: a brown/black object seemed to dart by the camera several times then disappear. Oh my god, is there something alive down there? Nope. It turns out there were some clumps of epoxy that literally looked like pieces of dog poop. They had only slightly negative buoyancy so if they were touched they would skitter across the tank like an air hockey puck. I luckily had an 18” long extraction tool and was able to reach in and pull them out. There were three different chunks and after I got them out I recognized it as a very hard/tough epoxy or polyester resin that I had seen used for tabbing when we stripped out the old icebox. I have no idea why they would be in the fuel tank but I’d say there is a 99% chance they were in there when Zia was built.
    7. I taped a brush to the end of the copper pipe and brushed the floor and walls to remove the attached grime. It was a soft bristle brush so I wouldn’t scratch the gel coat.
    8. Added the 5 gallons of filtered diesel to the tank and pumped it into the can again. This time it went very quickly and the little pump was able to move the fuel at its rated capacity of 30 gallons/hr.

    Here are my notes with 20/20 hindsight:
    1. There is no way I would have left for our previous voyage in the Pacific up to British Columbia knowing there was that much junk in the fuel tank. To me, it’s really surprising we didn’t plug our fuel filters at a bad time. From now on, I’m going to inspect and clean the tank every year. It won’t be a time consuming thing going forward.
    2. I started out with the copper intake pipe being too long (6 ft) and it got in the way. Trimmed it down to 40" which was much more maneuverable.
    3. At one point I tried using those fuel absorbent pads instead of cloth rags. No bueno. They broke apart quite quickly and cloth rags worked better.
    4. I taped my camera to the tubing with duct tape, but the diesel dissolved the adhesive over time. Need to come up with a better way of attaching the camera to the tubing. Maybe thick rubber bands?
    5. The endoscopic camera was for sure the way to do this. It takes a little practice to get used to. Bend the copper tubing a little bit where the fuel hose attaches. This gives you a reference point for rotating and swinging the tubing. Swing the camera left and right and up and down. Rotate the camera until it is oriented to match your motion before taping it down. Otherwise you have the strange sensation of moving it left but it appears to move right, etc.
    6. It was very good that I had a flexible grabber tool (see below) available to get the petrified dog crap out of the tank. I don’t think there would be any other way to remove it. Certainly a high pressure hose wouldn’t have washed it out, it barely fit through the 1-1/2” access hole.
    7. I was a little surprised that there wasn’t more water in the tank. In fact, I didn’t have any noticeable buildup of water in the R12T fuel filter.
    8. Next time I want to figure out a way to pivot the camera up so I can look at the top of the tank. Rick Dowe (on this forum) reports he used a mirror and was able to see that baffles were hanging down from the top. I think that's true but I didn't see them. I’d like to get some good photos of those for reference.


    Last edited: May 14, 2019
  2. scupper

    scupper Vern Gliot

    Apr 12, 2014
    Home Port:
    San Francisco
    Found the same "poop" in my tank. I was surprised to find that kind of debris that was obviously there from time of construction.
  3. rickdowe2

    rickdowe2 Richard Dowe

    Nov 29, 2013
    Home Port:
    Rock land,Maine
    When I had the fuel tank cover plate off for cleaning I put my phone inside and snapped several pictures. Of course I did not back pictures up at that time and they were lost. If I recall the top of the tank appeared to be glued to the underside of the integrated fiberglass structure with a black substance. I too found small bits of black crap in the tank. Luckily my tank was relatively clean.
  4. terry_thatcher

    terry_thatcher Terence Thatcher

    Jan 19, 2004
    Mark, you did this without taking off the steel plate on the top of the tank? What a job. I had my fuel tank and fuel professionally polished a few years back. Mine was so clean the guy gave up after an hour. No dirt was showing up in his multiple filters. (He advertises in 48 North.) But his process would not have removed petrified dog poop.
  5. mpearson

    mpearson Mark Pearson Staff Member

    Oct 18, 2012
    Home Port:
    Portland, OR
    Hi Terry - yes, this was without taking the steel plate off. The plate didn't look like it was very big and I didn't want to drill holes in the cabin sole. That's interesting yours was so clean and mine was so filthy. Maybe the previous owner had cleaned yours? But you've owned Adavida for a long time. Hmmm.
  6. schlepper

    schlepper John m. Harrison

    Aug 20, 2012
    This is a very timely piece Mark, thank you! I was readying for a Regatta in Sarasota Bay in late April and was motor sailing under a bridge... we got about 1/8-1/4 mile past the bridge and caught a puff of wind and healed.... when we healed, it wasn't long before the engine conked out. We went ahead with the Regatta of course, and then sailed all the way back to the entrance to the Yacht Club when we ran out of wind... got towed in... I thought I was out of fuel and that my gauge, which was registering 1/4 tank was in fact empty when I did the average burn rates on previous fill ups vs. hour meter.

    When we got towed the 150-200 hards to the fuel dock, we filled it up and it held 28 gallons. So there was approximately 12 gallons still in there. I turned off my auto-bilge switch just in case, as I had some diesel spill into the bilge when I filled up last year. But figured it was the fill hose and I would 'get to it at some point'... Now I am not sure if it's the fill hose or the steel plate, or the fuel hose or return line... or all of it?

    I was curious if anyone has the dimensions of the fuel tank. I know it's supposed to be 40 gallons, but have no idea of it's inside dimensions. Trying to figure if the degree of heel was enough for the pickup tube to have sucked in air.

    In any case, does anyone have a pictorial on how to remove that plate, what to replace the black rubber gasket with (or is it even rubber, and where do you get that type of diesel resistant product?), how to cut the deck so you can access all of it? Along with the holding tank in the keel and the galley counter coming across the centerline of the companionway, this fuel tank thing is a design fail in my opinion. That is too important an item to have it where you cannot easily service it.
    Last edited by a moderator: May 24, 2019 at 9:35 AM
  7. jimcleary

    jimcleary James M. Cleary

    Jun 23, 2001
    Home Port:
    Floral Park, New York

    Did you inspect your fuel filters after the engine quit?

  8. mpearson

    mpearson Mark Pearson Staff Member

    Oct 18, 2012
    Home Port:
    Portland, OR
    Hi John - so did your engine start up after getting fuel? Without changing the fuel filter or bleeding?

    From my measurements/observations, the tank seems to actually hold approximately 40 gallons. There is a little sump area where the intake is located so I would say you'd need to be down to a few gallons before normal heeling could affect the intake. It seems you still had 10-12 gallons so I wouldn't think that would be the issue.

    After we installed our new engine, the first time we did significant heeling the engine quit shortly thereafter. I primed/bled the fuel line and it worked again and has always worked since. My theory was there were air bubbles someplace in the fuel line that moved around because of the heeling.

    Dimensions? It's an odd shaped thing because of the way it's fit into the boat so full dimensions would be kind of complicated, I think. In general, I believe it's about 38" from front to back, and I remember it was 11" deep where the access port is. I don't recall seeing a drawing of the fuel tank and if anyone has one, please post it.

    Design Fail? I don't know if I'd go that far. I'd probably call it "sub optimal". Like most boats built back then (and some built today) there wasn't always a lot of thought/design put into all aspects of access & maintenance. It's like I tell new crew during the safety briefing: Zia is one big "tripping hazard" because she was built before the term "tripping hazard" was coined/invented.

    This winter I might try to figure out how to retro-fit a better way to easily remove the plate for access to the tank. I did all of the cleaning described above by going through the 1-1/2" hole where the fuel gauge is placed.

    Gasket Material? I went to an automotive store and explained what I needed and they sold me a little roll of gasket material for about $10.

    Last edited: May 24, 2019 at 10:25 AM
  9. john english

    john english Member

    Apr 7, 2015
    Home Port:
    Emeryville CA
    Easiest way to bleed is to install an inline Facet electric fuel pump mounted in the drawer space under the settee. Mount as close to the tank as possible to eliminate vacuum leaks.
  10. dave_a

    dave_a Dave Ahlers

    Aug 15, 2006
    Yes, John! And its a great backup for the engine's mechanical fuel pump. Belts & suspenders.

    I pulled out an incredible amount of debris (sheets of tar, bugs, who knows what) from my tank. I clogged up a giant Racor 700 filter cleaning the Morgan tank. I did this after watching the Coast Guard tow a Nonsuch into Oswego, NY after a failed very bumpy powered crossing of Lake Ontario. The constant pounding into a south wind stirred up all the bugs and tar. Fouled his filter completely. (It ruins your injectors as well long term). Swore that wouldn't be me!
    This is a maintenance issue. Deferred maintenance has its pitfalls....and you defer at your own risk.
    Every old diesel fuel tank has sludge & debris (IMHO).

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