Fuel Gauge

[rsotomayor]

I am having issue with the fuel gauge on a diesel tank. The dial moves to "empty " when the engine is off and moves to " full" when the engine is on but this cannot be right as we have run the engine on and off for about 4-6 hours.

How can one figure out where the problem is without taking the unit apart ?

Thank you.

RKS

 

[DougM]

You probably haven't run the engine long enough to get the needle to move off the full mark. (the gauge on my 323 takes half the summer to come off the full mark and then goes down rather rapidly)
As I recall the tank is rather flat and shallow, so it might take awhile longer. The sending unit in the tank is just a rheostat activated by the float lever. It appears that you have power, but double check the connections at the tank and also the back of the gauge to be sure they are tight. Also check continuity. Worst case is that it is the float switch in the tank which will be a major pain to change.

Worst case way to trouble shot it is to carry a spare five gallon container of fuel, and hope the tank doesn't run dry before the needle moves. One thing that a lot of people don't do if the gauge is functioning, is to watch the gauge as you fill the tank and chart the number of gallons from "empty" to 1/4, from 1/4 to 1/2, from 1/2 to,3/4, and 3/4 to "full" on the gauge. That helps to determine how accurate the gauge is and gives a clue as to gallons per hour usage..

 

[Ron20324]

Not sure what engine you have, but 323's expect to use a half-gallon an hour. YMMV. Especially if you've filled the fuel up into the neck, you just may not have used enough yet. I found, twice, that if the fuel guage reads empty, the 1/4 inch push-on connectors on the sender are loose, and just take them off and squeeze them a bit, and put them back on.

 

[rsotomayor]

Thank you, it is a Yanmar engine.
Will run the engine and keep a log.

 

[MSN-Travelers]

Not sure the year or your boat or if the fuel gage is from the same vendor.

My Bene has a fuel gage made by VDO. Troubleshooting guide attached.

Had the same problem as you when we took delivery on the new-to-us boat. Fuel gage showed empty with key off and pegged past full when the key was turned on. (right up to the moment we ran out of fuel)

Short version . . . Assuming the gage itself is functional, the gage (with key on) will read empty if the wire between the gage and the tank sending unit is shorted to ground and will read past full when there is an open (dirty terminals) between the gage and the tank sending unit. If your fuel tank is plastic, then there will be a ground wire from the tank sending unit to the negative bus bar and an open in this part of the circuit will also result in an always full reading.

I got lucky, cleaning the terminal connections at the tank sending unit fixed my problem.

Good Luck

 

[rsotomayor]

Interesting. Yes its plastic. There are two wires. So should there be a 3rd one ?

 

[rsotomayor]

I have downloaded the PDF guide, thank you very much. Will check the wires out using the guide.

RS

 

[MSN-Travelers]

Interesting. Yes its plastic. There are two wires. So should there be a 3rd one ?

If I recall correctly . . .

Power for the fuel gage comes off the key switch, goes to/through the gage, travels to the sending unit, through the sending unit and back to the boat ground buss bar. The dash gage moves so I will assume it is still functional.

A break in the circuit after the dash gage will result in the gage reading full (past full). I bought a 60 ohm & 120 ohm resistor from the local electronics store. I removed the two wire from the tank sending unit and jumped them with the resistors. The 60 ohm resistor should have the gage read about 1/3 full and the 120 ohm resistor should have the gage read about 2/3 full. If this does occur, then it confirms the dash gage is good and the problem is either the tank sending unit or the connections to the tank unit.

 

[rsotomayor]

Will check all this out- and will post whaterver works.

Thanks.

 

[GWG]

notorious unreliable fuel gauges

These fuel gauges are not worth much. Part of the problem could be the odd shape of the tanks. The best thing to do is fill the tank then keep a log of hours run and fuel used each time you top off the tank. Then you'll have a good idea of the rate of fuel usage per hour for your engine/prop combination.

 

[rsotomayor]

I had the tank checked and cleaned - tank was full so the fuel gauge is working fine- the engine had not been run long enough. But thank you for your comment. For now, just waiting for new sails to get out on the water.