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Discussion Starter · #1 ·
"Oh, by the way...." the boat's former owner said, as he handed me the key, ".... the fuel tank gauge doesn't work. Not sure whether it's the sender or the gauge." Ah blast - thought I - another "little" job. He told me how much fuel the engine burns per hour and that will help if I remember to record the hours every time we motor somewhere. Or I can do what at least two friends did to deal with the same problem: get a stick that would reach to the supposed bottom of their tanks, calculate the number of gallons a full tank would hold, mark the stick in units of one's choosing (usually gallons) and move on. I'm a bit more uptight than that about reliability and accuracy so I am considering replacing whatever has failed in the system. Components I can think of: sending unit, wiring and gauge. Is there anything else hiding in there? My real issue is the difficulty accessing and replacing the two terminal units, the sender and the gauge. I haven't investigated either but expect that like most items on sailboats, they will not be simple. Any words of advice (short of " hire a mechanic, stupid")? Anecdotes are even welcome. My research so far reveals a bunch of sending units and gauges available out there, none of which look "universal". On top of that the boat, a C&C 29 MK I, was re powered from gas to diesel some time ago and there don't seem to be a lot of associated service records in anyone's files. Words of advice joyfully accepted; commiseration appreciated; sympathy probably wasted - it's my own damned fault.
 

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Actually the units are (mostly) pretty universal. Circuit is pretty simple - the sender and gauge in series. The sender's resistance changes as the float moves up and down. Most common range is 240 to 33 ohms. This varies the voltage at the gauge. The Gauge is basically a voltmeter calibrated in tank level rather than volts. You can trouble shoot the system easily with a basic digital multimeter.
 

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Learning the HARD way...
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BOTH the sender AND the gauge need to be properly grounded... DAMHIK.
 

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Don't shoot me. Make a list of all the things you should repair, replace, or modify concerning the fuel system. Then arrange the current sender-gauge project to make
it as simple as possible and perhaps solve others at the same time.
 

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Learning the HARD way...
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When my boat was built in '87, the manufacturer installed a Moeller fuel gauge on top of the tank, which could not possibly be viewed by a human. The cockpit was about 2" over the gauge, and this was about 12" away from the lazerette. Here is a pic;

Fortunately, this gauge was set up to be used as a sender if a gauge was installed. Why they didn't install an electric gauge?? I can only guess... You can see the nuts that are used as contacts on the sender.

I installed an electric gauge next to the electrical panel, and initially figured that the ground for the electric gauge light was the ground for the unit.


When I went to try it, no reading... After hours of troubleshooting, and being trained to install gauges by the MMTA (see my signature), I went out and bought a new sender. More hours of installation and troubleshooting, and the I got the same result. "It must be a DOA electric gauge," I thought, and so returned the one that I had been trying to install. I installed a new gauge, same result...

Finally, I noticed the other ground lead on the electronic gauge and connected it. Voilla!:)
 
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We we replaced the tank in my boat with a poly tank from Moeller the sending unit worked fine for that season with the old guage. after that it stayed on 1/2 ever since.. I'm still not sure if that's 1/2 full or 1/2 empty.. ...:D But it's not a big issue I just open the lid to the laz and can see the fuel level.

Hopefully the new fuel gauge will work on the "old" Moeller sending unit.
 

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Discussion Starter · #11 ·
Why, Oh Why would anyone install a tank with the sending unit in such and impossible position. The tank in my boat also has very little room to even get to the sending unit, let along get the thing out! Ridiculous. Thanks, all, for your input. Still haven't made up my mind as to what to do.
 

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Why, Oh Why would anyone install a tank with the sending unit in such and impossible position. The tank in my boat also has very little room to even get to the sending unit, let along get the thing out! Ridiculous. Thanks, all, for your input. Still haven't made up my mind as to what to do.
solution :) = 4 1/4" round hole saw, 4" round hatch plate! = done!
 

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We've had good luck with CruzPro. You can program these things to compensate for any weird tank shapes and give you a very accurate reading.

But no matter how good the gauge is, I still find myself logging engine hours in boats and planes. Especially in planes, not good to run out of gas:) And I agree with Multi-girl...nothin's better than something you can eyeball.
 

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I changed the sender in January. It was a universal type and had to read the directions several times as there are two ways to install it. I thought I had the sender fully tightened down to the tank but about a month later found diesel fuel in the bilge and the sender was loose. Also, my tank is triangular and the sender is set in the deep part of the tank. Accordingly, the gage indicates there is more fuel in the tank then there really is...until the tank level gets low. I keep a log of run time after each filling to back up the gage, which I don't entirely trust. This was very important when we transited the Tennessee and Tenn-Tom waterways, because we motored almost every day for eight hours and fuel stops can be far apart.
 

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We're in the same boat:laugher with '85 C&C 32, gauge always indicates just above half full. You're on the right track on troubleshooting - gauge, sender, wiring. Check wiring first - black wire is ground, pink is from sender terminal to gauge (I've the C & C wiring code if you need it). We'll just get a matched sender and gauge and count on getting another 29 years without trouble, until it happens again. There is nothing overly marine about the gauges and senders, ours is in a Yanmar panel with Stewart Warner guage, so try automotive or tractor supply to save $$$ for the next project:cool:
 

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I have a persistent problem as well. It always turns out to be the connections at the panel or the sender.
 

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I have a persistent problem as well. It always turns out to be the connections at the panel or the sender.
There are basically three sending unit types that yield widely differing reliability.

#1 Elcheapo:Expected Life = SHORT These offer the absolute WORST reliability. I refuse to install them unless it is all that can or will fit the tank dimensions.


#2 WEMA Sender: Expected Life = Very Good: These senders are sold by Moeller etc. but are manufactured by WEMA. They are very reliable and WEMA has far more depths avaible than Moeller shows or offers. Moeller just rebrands the WEMA sender.


#3 Mechanical = Expected Life = Longest: These mechanical senders use a magnet that moves with the float. It is under the "capsule" so nothing electrical is in the tank. I have never once seen one of these fail. The capsule can be replaced with an electronic sender which gives you BOTH a mechanical and electrical sender!!


The electronic sending capsule for the mechanical gauge: Two screws and the mechanical gauge is now both mechanical and electronic... The utmost in reliable...


As one who is on the receiving end of these failures on a regular basis I have developed some opinions on reliability of fuel senders....

#1 Choice = Mechanical or mechanical w/electronic capsule
#2 Choice = WEMA - This is a close second and they are very reliable
#3 Choice = Elcheapo - Don't do it!!!
 

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Thanks for that helpful explanation Maine Sail. I've been wanting to add a remote fuel gauge to my boat (the current one lives under the quarterberth and is hard to access) and this helped me pick the correct type.

For anyone else who wants to find it, the part for converting a mechanical sender is sold by Moeller as a "Conversion Capsule". The part number is "MOE 035760-10". It costs about $50.
 

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Discussion Starter · #20 ·
Great and helpful responses! It looks like I will have to drill an access hole if I have much hope of replacing the existing sender. Maine Sail's info was particularly worthwhile. One of the intriguing things about sailboats is that every project is magnitudes larger and more complex than one originally assumed. Thankfully, or maybe prophetically, there is a large and diverse community like this one that has dealt with similar issues - no matter what they are - to whom I can turn. Many thanks
 
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