Fuel tank

(#131, Two Crows) is a 1982 Mk. II. Her aluminum fuel tank began weeping fuel a few months ago and I have now emptied the tank and removed it. The source is a spot of corrosion in the sump: gentle scratching with my screwdriver caused the disintegrating spot to open up to a 5 x 3 mm hole. I’m probably very lucky not to have the whole contents of the tank in my bilge. Don’t ever ignore fuel leaks. Now the tank is out and needs to be welded. The welder won’t touch it before I have it steam cleaned.
(A) Does anyone know of tank steam cleaning services in or near Toronto?
(B) I have been quoted $500 from one company. Does this sound reasonable?
(C) I want to install a visual inspection port. I am thinking of a 6″ circular opening with two aluminum backing rings holding a 0.5# plexiglass disk via 8 bolts and a rubber gasket. Does anyone have experience with or comments on that?
(D) Also, I was thinking of running a tube to the bottom of the sump to be able to manually pump out sludge/debris from time to time. Good idea?
(E) The tank was made by Unitech Manufacturing, Woodstock, ON – does anyone know how the baffles in the tank are arranged?
Thanks all, Boris Steipe, (#131, Two Crows).

a. I just added an inspection port in my SS tank and found baffles kept me from seeing and cleaning everywhere. Then I cut another one on the other side of the baffle only to find yet more baffles. It would take at least 4 ports to see everything so plan well before cutting. Also, I would worry about plexi plates because the plastic expands differently from the aluminum and it will leak eventually even if diesel doesn’t attack it. Sump drains leak, as well; better to suck up debris through a top-hung fuel pickup. Make sure your tank isn’t sitting in bilge water or on a soaked piece of wood; aluminum oxidizes to protect the surface but if it rubs on something it will keep deoxidizing and wear thru. Also, salt water in contact will wear a hole. These tanks often leak at about 20 years so anything we can do to prevent that is important. When you cut a port use aluminum plate, a nitrile gasket, and aluminum bolts (aircraft hardware) to prevent dissimilar metal corrosion. Make the tank thicker and it will last longer. By the way SS isn’t any better as I have learned with my water tank. John Gleadle (#181, Spinnaker).

b. When I installed an electric fuel gauge on my aluminum fuel tank I found:
1) Bottom of fuel tank has a slight v shape and slants down towards a 6” x 6” x 4” deep sump at one end,
2) One baffle in the middle of tank, and
3) Pick Up line was just above the sump bottom.
Respectfully, I am not sure if fiberglass panel would be kept clean enough to see anything. I would just cut a 4″ sq. inspection hole in the top above the sump and make a good gasketed cover for it. You could make a ” squeeze bulb ” thing long enough to reach the bottom of the sump (like a battery tester thing) to clean out the bottom of sump now and then. Anything that has vacuum would do as well.
Note: Measure fuel when filling up and note quantity @ 1/4 , 1/2, 3/4 and full as it’s not quite linear. That is very useful with electric gage. [Ed. Note: I use a wooden dowell to measure; I’ve had no luck with electric gages.] Good luck with this ……………. Frank Bryant (#186, Visitant).

c. Thanks Frank and John, useful advice. Yes, I would expect the plexiglass to age over time. I think I’ll just give it a try – if it holds up for less than say five years, I’ll replace with glass. Great idea about the squeeze bulb. Boris Steipe

d. The design of the fuel tanks called for a sump lower than the bottom of the tank and a pickup that went to the bottom of that sump so that you could suck any water or solid trapped in it. It had its own pickup on top of the tank. If this sump pickup is not there, it`s possible that the tank does not have a separate sump. Then, it is better to have the fuel pickup at the very bottom of the tank so that it picks up anything that could lie there including water and any solid. If the pickup is higher, like it is often the case, then solids and water will accumulate at the bottom and when the weather is bad, from the movement of the boat, will mix with the fuel and clog the filter at the worst time. As far as the inspection hole, I would not do it on my boat, because any opening below the top will eventually leak and you will have fuel in the bilge. Rubber gaskets are known to be eventually eaten up by fuel and leak. If the tank is full when it happens you will have to empty the tank to fix the problem. If you want a manual fuel level check, do the hole at the top, small, and use a dowel rod to check the fuel. The gasket should be of a material that is resistant to fuel (not rubber). Hope the above will help and have a great day, Marius Corbin

e. I don’t recommend an inspection port in the side of the tank or any opening except at the top. You would be initiating a chance of a leak. Your proposed method could result in attack of the gasket/caulking by the fuel over time as well as differential expansion between the Plexiglas and the aluminum. I have used a dipstick successfully, a piece of wood dowel marked in inches, litres or gallons, and inserted by a removable plug on the tank top [Ed. Note: Over the deepest part of the tank]. It is crude but trouble free. You probably know that there are commercial level gauges that use hydrostatic pressure with a small nylon tube inserted from tank top to the bottom. See http://thetanktender.com/ An ability to pump out the sump is also a good idea, again using a tube from the top of the tank. For example, use a suction pump with a piece of copper tubing extending to the tank bottom. I insert mine through the dipstick port! An engine oil vacuum suction kit could also be used for this job. See Bigboy Topsider. I have one of these but have not used it for fuel. It should be OK for diesel (not for gasoline) but you should check compatibility of the gaskets.
Regards, David Salter (#050, Opportunity)

f. My aluminum fuel tank is underneath the pilothouse sole. I was going to add a similar port so I found some cleanouts at Fisheries Supply in Seattle. They’re called Seabuilt tank access plate system. I was able to pull out the tank sender and see the baffles. My tank has six compartments. That’s when I gave up. I didn’t want to put six access hatches in. I bought a paste you can get from the home heating industry that detects water in diesel fuel. You rub it on a stick and dip it into the diesel fuel to detect water. I was able to access my fuel through the sender hole. I had no water in my tank probably because the fill is underneath the cockpit seat. [Ed Note: You might also want to buy a filter that removes water [Funnel Fuel Filter.] Regards, William Schmid (#174; “Anakena”).