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Old 03-11-2008, 13:57   #1
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Planning on cutting diesel tank

So I was replacing my sender on the diesel tank the other weekend and I noticed that the bottom of the tank had a ton of gunk built up. Im thinking next weekend I will cut a hole into the top of the tank, where the sender unit is now, making the cut round and about 8 inches in diameter, so I can drain and clean the bottom of the tank. The holes would have already been drilled around the edge of the cut at this time (to get all of the metal shards durring the cleaning, and then sealed with a gasket, pop rivited into place and caulked around the edge. The sender would then have the same done (without being pop rivited, just screwed).

Any problems you can forsee with this idea? Any better way of doing this task? By the way, the tank is a 66 gallon stainless steel tank.
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Old 03-11-2008, 14:20   #2
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The only problem I see is that the stainless is going to be a bear to cut. The overall arrangement sounds similar to what I already have. I don't think I would pop rivet the access plate because sooner or later you'll want to get in there again for cleaning.
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Old 03-11-2008, 14:27   #3
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What you want to do is cut the hole and maybe a few more as there usually are baffles you need to get around too. I would guess at least three depending on how flat the tank is. Cleaning 1/3 of the tank is only better than nothing at all. After the hole is cut you need a plate with a gasket. You drill the holes and tap them with threads and screw down the plate and gasket about 1/8th inch thick, screwed every two inches or so. You really don't use pop rivets as they won't be tight enough. This way every 5 years of so you can repeat the exercise. Do the same thing on the water tank">fresh water tank too. Inspection ports I believe can be purchased to make that job a little easier. The hole is not a precision operation so plus or minus 1/8 inch will cover the plate and gasket.

The other way is to use a service. They can put in two hoses about the size like the hose at a gas station. They connect it up to a pump that usually is about 400 gallons per hour. They use a filter system with gages and can power wash the inside of the tank using diesel fuel. It can be exceptionally effective and can be done in about 3 to 4 hours. You just pop in the hoses and change the filters as the pressure drops. After 4 or 5 filters you are done. It works best if you have about 8 gallons of fuel in the tank so it can be cycled through the filters enough times to get out all the gunk. A full tank is going to take all day.
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Old 03-11-2008, 15:21   #4
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Hello SM:

I have just completed the same chore but with Aluminium tanks. Here is my experience and hopefully you will learn from my mistakes.

My tanks were under cabinets so I was limited as to where I could drill the holes. The best tool for cutting the tanks is an 8" hole saw. Any smaller hole and it is difficult to get your arm into the tank to clean out the gunk. I had had my tanks cleaned professinally with a service like Paul was talking about and it didn't work so well. I had a welder build a rectangle from 1/2" x 1" aluminum and then cover that with 1/4" plate. I then drilled the holes about every 1 1/2" around the perimiter. I tried to seal this with permatex. It did not work well. I finally had to buy some nitrate gasket material. Conclusion. Unless you really like making things yourself I would buyt the premade diesel access ports. Seabuilt - Access Plate Systems

When laying out your main hole make sure that there is enough room away from the edges and the baffles to get the rim of the ports to set properly. If I were to do it again I would use self tapping screws to hold the port lid in place and then drill the screw holes of the lid thru the lid itself to ensure accuracy.

The baffles can be difficult to locate since they do not neccissarily weld the baffle to the topp of the tank. I used an existing hole in the tank and then was able to track down the baffle welds on the side of the tank.

To clean the tanks I used the following tools: 1) plastic scraper ( to get the big chunks out), 2) rags to sop up the last bits of diesel 3) paper towels and multipurpose cleaner to get more stuff out of the tank 4) scotch brite pads to get all the scunge off the sides and bottom of the tanks, 5) a shop vac to suck out all the metal filings out of the tank when there was no diesel left in the tank. It worked well but it was very time consuming.

Here is a link to a couple of other threads:

Fuel Tank Acces Ports

What's in Your Tank

Good luck let us know how it worked out.
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Old 03-11-2008, 17:54   #5
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Great responses! I think I will go ahead and make one hole after feeling around with a stick so I wont cut anything important. Afterwards, I will make up to two more, the same way, if there are areas I cant reach from the first. I guess I have to get the premade ports, a tap to make the threads, and cleaning equipment. Thanks again Pblais, Charlie, and Cabo sailor.
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Old 03-11-2008, 19:46   #6
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Hi Monkey! Just in case you need this knowledge, and to save ya a fortune in cutting and drilling tooling; Condensed milk is one of the best stainless steel cutting lubes known to man. I just finished drilling and countersinking about a hundred 1/4" to 5/8" holes in 3/8" 316 stainless for chainplates. Kept the cutting area bathed in condensed milk and kept the drills and countersink making chips, and I still have the same bits to use over again. No kidding! IMHO, Chris
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Old 03-11-2008, 22:23   #7
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Originally Posted by stoupidmonkey View Post
Great responses! I think I will go ahead and make one hole after feeling around with a stick so I wont cut anything important. Afterwards, I will make up to two more, the same way, if there are areas I cant reach from the first. I guess I have to get the premade ports, a tap to make the threads, and cleaning equipment. Thanks again Pblais, Charlie, and Cabo sailor.
You won't need taps with the premade ports.
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