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Fuel gauge troubleshooting

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More than likely, when your fuel gauge starts acting up, it is the sender. But...check the gauge first to see if it is an electrical issue. Over time, surface corrosion will build up and finally overcome the sensitivity of the instrument. Loosen all connections on the back of the gauge, hit with some 180 or 220 grit, then re-install and see if that corrects the problem.



If the gauge is still not working, time to head to the fuel sending unit on top of the tank and do some more troubleshooting. The sending unit should be accessable under the console on center console boats or under an inspection port in the floor on walk-arounds and dual consoles. Once you have access to the sender, disconnect the wire running to the gauge (pink). The fuel gauge should now read EMPTY. Take the same wire and ground it against the green ground wire on the tank and it should read FULL. If the gauge is kind of bouncing around during this test...there is another loose connection somewhere in the circuit and you need to trace the wires and correct the issue.


At this point, if everything reads good so far on the gauge, then the fuel sender is probably bad. Unfortunately, to accurately test it, you need to remove it from the tank. Be careful removing the 5 screws holding it in place as it is easy to strip the threads in an aluminum tank. Remember this when re-installing the fuel sender, too.


Once out, you will need a multi-meter to test it. Set the meter to read ohms and connect the test leads to the screws the wires were attached to. With the float arm all the way down, you should see around 230 ohms; all the way up (remember, this is in relation to how it would float in the tank) you should see around 30 ohms. If your readings are off, good chance it is time for another sender.


American senders are about 230 ohms at low and 30 ohms at high (full).

One suggestion on a replacement sender...consider spending a little more now and get one with no moving parts! This type eliminates the wildly swinging fuel gauge readings in rough water and seem to be much more accurate that the float arm style.


On installing the new sender, follow the manufacturer's instructions, but be careful to no over-torque those screws!

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This is the one thing I do not like about my yamaha command control plus gauges, I do not trust the fuel levels at all. I use the fuel burn numbers which should be accurate since the number is coming from the ECM. My tank is 139 gallons and anything below 35 gallons the gauge is telling me empty.


Thanks for the tutorial.

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Good info!


Coincidentally, I was just on an RV forum and there was a long discussion about fuel senders there too.


I posted this...

I ran out of gas in a boat many years ago (another story that pretty much starts like a: "Hey y'all. Hold my beer and watch this"), and vowed to fix it (ie, calibrate) and never do it again. Conclusion was that the float-type sender mechanism wasn't very accurate in its basic design, and couldn't be improved. When I started flying, I remembered my past and tried to calibrate the airplane's gauges - thinking surely they had to be more accurate. Nope, pretty much the same story.
However, some senders (like the capacitive-type, $$) that are designed as precision/adjustable units can be made to read just about spot-on, but it seems the simple float-type are just that - simple.


I've learned that the float-type seem to only tell you if there's likely "some" amount of fuel in the tank... you have to judge whether "some" means full, less-than-full or none (engine will tell you if it's 'none'). Kinda like some people driving with their turn-signals on around here - it only means the circuit and bulbs are working.



Sorry, I'm rambling here. Was going fishing, but thunderstorms rolled in. :ball:

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