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  #1  
Old 05-14-2013
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Fuel gauge reads empty

Last fall, right before winter lay up, I filled the fuel tank and the gauge read "full." Boat was splashed the other day and I notice that the gauge now reads "empty." There isn't 27 gallons of diesel in the bilge so I assume the tank is still full.

Somewhere recently I read great directions for diagnosing problems with fuel gauges, but now cannot recall where I read it. Sort of an idiot's step-by-step guide. (Which, sadly, is what I need.) Anyone point me in the right direction?

Oh, and I know that real sailors just monitor engine hours. I do too and know that I burn about 2/3 gal./hour at cruising speed. But, I'd still like to fix the gauge as it is a nice approximation and it kinda freaks me out to see the needle on "E"
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Old 05-14-2013
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Re: Fuel gauge reads empty

did you dip the tank maybe someone needed the fuel more than you. boat are easy to siphon when on the hard. when i was a kid it keep my seagull outboard going all winter. and fuel was 21 cents a gallon but a longer walk from the water
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Old 05-14-2013
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Re: Fuel gauge reads empty

Every gauge problem I've ever had like this has been at the connections on the tank or behind the gauge. Take them off, clean them up or replace them and I'll bet you're back in business.

Sometimes a squirt of electrical cleaner will do it. Other times, I get in and rough the surface of the connectors up with a small file or sandpaper. Often, I just snip them off and crimp on new ones, as they look old and crusted over. Cleaning is always temporary, eventually I end up at the replacement stage.
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Re: Fuel gauge reads empty

What kind of sender does it have? I know on my old MG the float cracked and filled with fuel, and read empty for a few years. Took a while to make it to the top of my "fix list," but I would suspect the connections. Generally it is a simple system and start with the connections then check sender, and then gauge. A multi-meter is going to be your friend if it is not just a corroded connection.
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Re: Fuel gauge reads empty

Now that I think about it, I have had a sender go bad, but it was on a holding tank that just corroded it to junk. Never on the fuel tank, but its certainly possible.
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Re: Fuel gauge reads empty

Put a meter across the connections and with the engine switch on (ignore the alarms) you should read some value of over 12v - the same at the back of the gauge as on the tank.
If you get that it's not the gauge, the wire or the connections. Pull the sender and replace (varying cost from 29 bucks to 100+).
If you have power at the tank but not at the gauge you'll have to check the gauge via resistance check (meter on ohm's and a connection to each end of the wire). You should read a small amount of resistance. Infinite resistance indicates an open circuit, bad gauge. You can always check a meter's resistance/ohm reading by simply touching the red to the black - that's what good wire looks like. Then touch both to a working light bulb (connector on the base and other on the socket), that's what a working circuit with resistance works like. Everything that uses (consumes) electricity has some measure of resistance.

Then check the wires the same way (a long extension will be needed for your meter). Ditto, a small amount of resistance indicates the wires are good, infinite resistance means air gap, i.e. open or broken wire.

If you don't have power across the connections at the tank you'll have to check the other (source) end of the wires to make sure there is 12v there (usually 12v is provided from the engine harness - a take off from the alt since you only need fuel levels when the engine is running). You'll have to trace that out as each boat installation is different.
Once you think you have the right wires do a resistance check as described above just to be sure.

If you don't have a meter, when you get one (not if, when) get a digital one. Analog meters are not sensitive enough. Buy a spool of 20 feet of cheap wire and some small alligator clips too so you can make extensions.
Do voltage checks with the ignition switch on (or running if the alarms get to you). Do resistance checks with the ignition off.
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Re: Fuel gauge reads empty

One other thing, you might want to double check the tank and make sure you really did fill it up, or someone didn't help themselves. I know I have found myself empty when I thought I should have had more fuel.
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Re: Fuel gauge reads empty

Hmmm, I'm sure hoping that no one helped themselves. I tend to be pretty trusting so that thought had not occurred to me. I know I filled the tank right before I had the boat hauled. Also, the fuel gauge needle was on "F" as of a week or so ago when the boat was on the hard. Now, in the water, it's on "E"

I did start the engine and ran it for about 25 minutes in the slip. So, there was at least some fuel. And no hints it was low.

Maybe a connection got knocked loose during launch. If not, I'll check for corrosion as Minnie suggests. No easy way to check the fuel level in the tank other than thumping it as there is no access port (other than for the fuel float).

Chuckles, thanks for the tip on the multi-meter. That's on my purchase list. Should have one anyway, I guess, and learn to use it.

I appreciate all the advice.
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Re: Fuel gauge reads empty

I had a fuel tank sender go bad on my previous boat. They are all pretty standard. The sender is just a variable resisitor. It changes value as the float goes up and down. The gauge and sender and just in series across the battery. Voltage across either should be somewhere in the middle between 0 and 12 volts.
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