Fuel tank cleaning

[Sprig1]

Just cleaned my 72 gallon aluminum fuel tank. I cut three 4 inch holes in the top. I'm making 6 inch aluminum cover plates and screwing them down with a rubber gasket. There was about a 1/4 inch of sludge and water in the bottom. I wiped it out with a sponge and then used naphtha and finished cleaning with acetone. I'll vaccum it out to get all the aluminum chips. I thought it would of been a lot dirtier. I don't know if it was worth it or not but at least I want be wondering. There was some pitting in the aluminum but not to bad I hope. What do you all think of putting the tank back in on an angel so all the water collects on one side? It was good to start working on the boat again have to get it done.

[kerrye]

A deliberate low point with a drain seems to me like a good idea on a diesel tank, kind of like a water separator.

[Sprig1]

I wish it had a low point just one big wide flat bottom. I guess I could take it to someone to tig weld one in. I
don't think my mig welding skils on aluminum are up to the challenge just yet just learning how to do it.

[Beta Don]

If it took 30 years to develop 1/4 inch of sludge on the bottom of the tank I would think if you're careful with what you put in it you should be good for at least another 30 years - Assuming you get good seals on your new cover plates

Don

[smacksman]

Free State has the same tank. Cruising down the ICW was not a problem, but as soon as we got bounced about in the Gulf of Mexico it stirred up the sludge and gave me problems and I had to change the primary filter while being tossed about 10 miles offshore. If I didn't have a day tank fitted I would have been stuck. The 12 gal. day tank gave me 10 to 12 hours of motoring and overnight the sludge had settled allowing the day tank to be filled again.
When the motion is very violent there was a clang noise from the tank as though a baffle was being thrown about. Did you find you had a baffle plate in your tank?

[kerrye]

That's a good point. What's your day tank like? A 5 gallon gasoline outboard tank modified to accept a diesel return line might be good insurance.

[kerrye]

A hint for fuel tank cleaning. I once had to clean out the diesel fuel tank on my Mercedes 300TD but didn't want to be vacuuming diesel fuel and sludge directly into my shop vac. So I took a 2 gallon plastic bucket, put the lid on it and cut out two holes in the lid--one for the end of the shop vac and the other for some 3/8" fuel line. I stuck the shop vac into the hole just a short ways and sealed it up with some tape. Did the same with the fuel hose and then turned on the shop vac and used the fuel hose to vacuum out the tank. The liquids dropped out into the pail rather than being sucked into the shop vac. One advantage of a system like this is that the fuel hose is small and can be inserted into the tank thru the fuel sender opening to suck everything out.

[smacksman]

Kerrie, my daytank came with the boat so I don't know its pedigree but it is red plastic so must be for gas originally. Located in the bottom of the starboard deck locker. It measures out at 12 gallons capacity. A small electric pump sucks from the main tank through a filter with a pressure gauge in line which indicates when a filter change is required. The supply from the little transfer pump is valved then tees into the return line. A combined fuel supply and diesel return fitting is on top. The diesel supply line has a shut off valve and another filter in the engine compartment.
If the day tank gets dirty it is easy to remove and clean.
The big test is to remember to stop filling the day tank before it overflows!! It takes about half an hour to fill!



The transfer pump setup with the switch on the right.



The day tank

[kerrye]

Does your engine run just off your day tank or there lines to the engine from both tanks with switchover valves?

[Sprig1]

Hi smacksman there where two baffles in the tank almost welded solid all the way around I don't think they could come loose. My sending unit was totaly rusted and wasn't working. I really only took it out after reading about the problems you had. It was more for a piece of mind. I'm moving the holding tank back to the starboard lazaret the way Don has his set up. It's much easier to install with the fuel tank out.

[rnummi]

Kerrye: brilliant idea! I bought an oil changer www.mityvac.com 7300 that works off a Venturi principal with a air compressor. Basically I think it would work much better if it had suction like you described. Thanks for the great tip. This is a great thread, in going to hunt down a day tank tomorrow. Sprig, what did you use to cut your tank open?

[Sprig1]

I used a 4 inch hole saw. Surprising how fast it went through. Filled holes with six inch round patches screwed on. With rubber gaskets. Haven't done the patch yet have the rubber gasket material in diesel fuel to see if it reacts.

[Beta Don]

I've seen other tanks with clean out holess like you're describing. I think your 6" cover plates need to be a good bit thicker than the tank material to ensure a good seal (1/4" minimum) and you need at least 8 screws evenly spaced to hold them down. Even though they are in the top of the tank, if you don't have a good seal they will leak like crazy when the boat tosses around. Usually the screws are not sheet metal screws, but are machine screws drilled and tapped into the tank. The rubber gasket for the tank sender would give you a good idea of what the gasket material should look like. I would buy something specifically rated for use on fuel tanks rather than hoping some unknown material would stand up to many years of exposure to fuel

Don

[smacksman]

Does your engine run just off your day tank or there lines to the engine from both tanks with switchover valves?

No, the engine just draws from the day tank. If the fuel transfer pump failed I could 'short circuit' it and join the fuel lines for a direct supply.
I usually cruise dawn to dusk so 12 hours is about tops and gives me about a 100 mile run. If I need more than 10 to 12 hours running time in a day then I just run the fuel transfer pump for 10 minutes about noon.
The day tank has a crude fuel level gauge but I tend to use a wooden dowel to dip the tank through the filling cap.
Only once did I use my 5 gallon can of spare fuel and syphoned it through the day tank filler cap. As it turned out the extra fuel was not needed but it was good 'insurance'. Bleeding the fuel system while bouncing around in 2 foot waves at 2 seconds intervals was NOT something I wanted to have to do!

On a side line - how to syphon diesel from a can without the taste.
Rig the syphon line, then take a short length of hose and insert it into the can ABOVE the surface of the fuel. Wrap a rag round the pipes at the mouth of the can and BLOW into the short length of hose. This pressurises the air above the fuel and forces fuel out through the syphon line. Finally take the rag away to let air in. Here endeth the first lesson

[Sprig1]

So I have my plates all made I ended up using 1/2 inch aluminum plate that's what I had. The more I read the more confused I get. That's what the Internet dose to me. I drilled and taped the holes for 10-24 stainless steel screws. The question is the gasket. I did everything Don told me too 8 screws around the top thicker plates. In the old days it would of been some gasket material I cut out and some permatex and that would of been good. Now nitrile, vitron and a host of other things you can't pronounce and cost a fortune I have good old cork gasket material thinking of getting some rtv permatex and smearing it on both side and calling it a day. It would seal the screw holes and everything. Any thoughts. On a lighter note I got about 1/4 inch of gunk out of the tank and had it in a pan I was wondering how much water was in it so promptly spilt it all over the floor of my shop mostly water it was a mess.