1974 18' CC fuel tank sending unit

mikeyk · #1 02-18-2019, 07:39 PM

I've searched posts but can't seem to find any information. I need to replace a faulty sending unit. Can it be accessed by de-caulking and removing the 6"x6" access plate under the front of the console seat?
Or should I prepare myself to pull off the console and lift off the entire tank lid. Just praying the last time the cover was serviced they didn't use 5200 .
Maybe someone has done this before and measured x,y coordinates on the lid where I can hole saw access to the sender?
Thanks

uncleboo · #2 02-19-2019, 08:06 AM

Hey, Mikey! I can't give you the precise dimensions as the hatch has been repaired. Go check my thread ' deck replacement' and you can see everything under your deck. The 6 x 6 isn't going to access anything. Is there an inspection plate toward the front under the console? If so, you can use a mirror and tape measure and get a close idea where to cut a new 6" round access plate. The sending unit will probably be near the middle/rear of the tank if it's original. Best I can do is show you the pic of the hatch removed, maybe you can get an idea by scaling it. Good luck!

http://www.classicseacraft.com/commu...1&d=1550577922

uncleboo · #3 02-19-2019, 09:44 AM

By the way, my old tank was a 30 gal. and was slid all the way to the rear of the compartment. When I replaced it, I had a 35 gal tank made and slid it as far forward as I could to improve the center of gravity, since I will be running a DF 140 4 stroke. (hopefully next month!)

mikeyk · #4 02-19-2019, 02:06 PM

Thanks for the information. Now that I have the inspection lid off I was considering running my LED cable lens that plugs into my Android device and locate the sending unit. If it's under the seat cover, it would be worth taking out a plug to access it. If not, I'll pull the console and the tank lid, and install an access hatch so any sending unit service can be done without pulling the console.

uncleboo · #5 02-19-2019, 05:15 PM

Good luck and keep us posted.

mikeyk · #6 02-21-2019, 11:31 PM

So I unscrewed and tilted the CC off the coffin cover over the fuel tank. Thankfully the last idiot (you'll find out why I call him that further in this reply) didn't 5200 down the cover, although he used a mixture of polyester resin and silicone. Apparently he was too lazy to clean and prep the surfaces which was good for me because it broke loose without too much swearing. The fuel sending unit, what was left of it, was installed exactly in the center on the top of the 40 gal. tank. The top plate of the sending unit was nothing but a pile of rust and there was a 1"hole. I was able to fish out the rest of the sending unit rheostat/ float assy. which turned out to be a Bosch automotive unit, not marine...AND it still worked when I tested it. There were exposed corroded wires where the leaking gas had dissolved the jackets of the non-marine thhn wires, 10 ga!) used to connect the ground and gauge. The leaking gas had also dissolved the jacket of the fuel hose down to the braid.
But I am ecstatic. Had it not been for the fuel gauge not working, I would not have discovered these until some catastrophic break down far from shore. The guy who sold me this boat obviously knew there was a leak but didn't tell me.

dginge · #7 02-25-2019, 12:07 AM

Is the tank original it sounds ? Hate to kick this to you but why not replace the tank while you are in there? It needs all new lines of course. Just my .2 cents

mikeyk · #8 02-25-2019, 12:55 PM

Tank is not leaking and it's questionable to justify the labor and expense of fabricating a new tank just as a precautionary measure. I have replaced leaking fuel tanks in other hulls and in all those cases there was never a catastrophic failure of the plating or welds themselves, rather a nuisance seep at a cracked weld seam or, in the case of aluminum tanks, electrolysis where a disimilar metal hose fitting was threaded into the tank.
The tank is 1/8" TIG welded stainless. Replacing all hoses while lid is off as well as rehabbing lid by getting rid of 3/4"ply core with Airex. That should take at least 50# of weight off the boat. Also installing flush inspection plates over sending unit and outlet so future inspection or service won't require lifting off center console.
No signs of electrolysis visible on top of the tank or welds. Ran LED borescope in thru the sending unit cutout to inspect inner tank and welds. Only way to inspect tank outer sides and welds concealed by the foam liner would be to do a destructive removal of the tank itself. Once the new sending unit is installed, I'll pressure test at 1.5-2.0 psi.

dginge · #9 02-25-2019, 10:52 PM

Excellent. Sounds like you have done it right. Good intel

Quote:

Originally Posted by mikeyk

Tank is not leaking and it's questionable to justify the labor and expense of fabricating a new tank just as a precautionary measure. I have replaced leaking fuel tanks in other hulls and in all those cases there was never a catastrophic failure of the plating or welds themselves, rather a nuisance seep at a cracked weld seam or, in the case of aluminum tanks, electrolysis where a disimilar metal hose fitting was threaded into the tank.
The tank is 1/8" TIG welded stainless. Replacing all hoses while lid is off as well as rehabbing lid by getting rid of 3/4"ply core with Airex. That should take at least 50# of weight off the boat. Also installing flush inspection plates over sending unit and outlet so future inspection or service won't require lifting off center console.
No signs of electrolysis visible on top of the tank or welds. Ran LED borescope in thru the sending unit cutout to inspect inner tank and welds. Only way to inspect tank outer sides and welds concealed by the foam liner would be to do a destructive removal of the tank itself. Once the new sending unit is installed, I'll pressure test at 1.5-2.0 psi.