Replaced fuel sending unit
 

End of last season dashboard fuel gauge was bouncing around wildly from empty to 3/4 full.

Didn't find any lose wires, so figured it was the fuel sending unit.

Fairly easy job under the deck plate. Original fuel sending unit looked ok, corroded sections as to be expected.

Have to follow the directions carefully to cut and then position float arm based on the chart for fuel tank depth.

Nice and dry under the hatch, peeking under with light wood looks bright / fresh as original.

Will find out shortly if the sender had gone bad.

Somewhere on here Tsubaki has a good thread about testing fuel senders.

You can test very easily with a multimeter set to the ohm scale. If you connect the leads to the two sender connections and raise the float. The resistance should change corresponding to the position of the float arm. The sending unit is basically just a variable resistor.

Regarding my old V20 1974 with saddle tanks, were there fuel senders and fuel level gauges? I don't see any wires on top or on the sides of the twin 20 gallon gas tanks. Could the sender connections be behind the tank against the side of the boat? I was reluctant to pull the tanks if I didn't have to.

I am presently in process of replacing all the gas lines and adding a big new removable filter like we see in car engine oil system. This boat has been sitting idle since 2001 or possibly before that!

Larry

I had a 76 with same tanks. no sender on them eaither, but I did not mind as when one tank went empty I would switch to the other and knew when to head home. Later when I converted mine to OB I added a third tank were the motor use to be and never worried again!
By the way I have never had a working gas gauge on any boat, and have never run out, by filling after each trip.

Since I wrote that I have pulled the tanks and my boat expert and I saw an old level sender unit on top of each tank. He said those are essentially "always" non-working after sitting this much time, but that new senders are quite reasonable, $35 or so. It needs to be 17" for my saddle tanks.

But I will need to either add one gauge and a switch or two gauges on the dash somewhere. This boat apparently never had fuel gauges. There was a piece of round doweling in the boat, and I would bet that is what the fisherman used for their fuel level.

BTW, I dumped both tanks into plastic gas containers and poured about 7 gallons of that stuff into my Durango gas tank (which had 3/4 of good gas). I saw several discussion comments wherein boat experts suggested that because a car's fuel filters are really good, and because the dilution of that much good gas will make that old gas and oil mixture harmless.

I drove the Durango today and noticed nothing different.

Larry

I connected an ohmmeter to the sender units before I installed them inside the tanks. I see the resistance changing as I lift the float. My question regards calibration. If I connect a meter in series with the sender, and 12v to the sender, how will I set the meter to read zero when the tank is empty and full with the tank is full? I don't see a rheostat or other way to calibrate the system...

Larry

You can't calibrate... You have to buy the correct range sender for your gauge
Then it's just a matter of setting up the sender so that the float maxes out at the top and bottom of the tank

best is to fill up, reset odometer on gps to 0,run 40-50 miles, fill up, calculate mpg. keep track of mileage as you burn fuel. i can usually tell how many gallons i will need within 1 or 2 at each fillup.

I've been using the wema senders lately, I can't say they are any better(time will tell) but they sure are easier to install. Measure the tank, order the sender that's the right length and install. No bending or moving the float around. As far as testing them, I ground the pink wire to the ground wire on the sender, if the gauge buries itself, then its most likely the sender. If the gauge doesn't move, check the wires, power and ground to the gauge, then ground the pink wire at the gauge, if the gauge doesn't move, the gauge is bad. If you want to get real fancy, Lavorsi sells a sender that once its installed, you empty the tank(leave a couple gallons just in case), turn the screw on the pot till the gauge reads empty, then fill the tank and set the other pot till the gauge reads full. Regardless of what kind of gauge or sender you have, its only going to so accurate due to the design of most boat tanks