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New Fuel Tank Port(s)

Posted by Chris Crighton 
New Fuel Tank Port(s)
March 06, 2009 03:29PM
[This article was originally contributed to the old website by Bill Solberg, Tartan 3800 #9.]

We often need to clean out our diesel fuel tanks but there is usually no inspection port on the common aluminum or fiberglass fuel tanks. What are the options for adding one or more ports? By the way, most inspection port manufacturers do not recommend installing inspection ports in gasoline tanks.

Cutting the hole(s). Pump out the tank then fill it full of water before cutting the holes for the cleanout port(s). One owner used a holesaw with a metal cutting blade - pictures are on Yahootartan sailing gallery for which you need an account to view. [http://ph.groups.yahoo.com/group/tartansailing/photos/view/10fd?b=44 ]

Installing the port(s). The best port design is one with a raised collar, like those on gasoline tank trailers you see at the filling station. That they don't make better ports goes to the usual dollar bottom line. One recommendation is http://www.seabuilt.com/ Installation instructions, more photos and an animated gif demo are on the site.
That said, the trick in making ports is to get a good grip on the thin aluminum sheet metal of the tank proper. The caps can be as thick as you like, but you still have to deal with the tank material. Start with a rather fine thread for the fasteners, at about 1 inch apart all around. The caps should be about 6-8 inches wide. The fasteners should be rather fine thread because when they strip out after repetitive removal and tightening, you'll have something bigger to tap up to. Get your rubberized cork gasket material from a professional seal/packing company like (Allied Packing, Long Beach, CA). Some have reported using a rubber gasket cut from a sheet of rubber the same thickness as a truck inner tube has never leaked. While you are at it, order some extra nitrile O- rings for the fuel fill cap on your boat (send them a sample). The nitrile will last indefinitely. Use a good fuel-tolerant gasket sealer (Permatex is suggested) on the bottom side of the cork gasket. Use some on the top if you detect that there is some leakage. You can also rig a special 1/2" pipe thread port system to accept a pressure valve fitting so as to pressure-test the tank. This is a bit over-kill, as many tanks will likely show some leakage, even though there is minimal or no actual fuel leakage.