Correcting Fuel Sender Measurement

[Jason2tpa]

1998 S115TLRW, 1976 Aquasport 170

When I bought my boat and motor the fuel gauge wasn't working. Previous owner stated it needed a new fuel sender. So I installed a new one, my first time making such an installation, and it works. However, for the past few months since owning I've noticed that when the gauge reads "E" and I fill up the tank, at most the tank will fill at around 15 gallons. The previous owner told me it's a 30 gallon tank, though this boat was originally installed with a 27 gallon tank. I have not visualized the entire tank, not wanting to break open the deck seal. Highly unlikely it's a 15 gallon tank, more likely the fuel sender is reading an incorrect level due to my installation. If I remember correctly, the instructions had me break off a particular length of rod the float slides up and down on. I followed the directions to a tee.

Suggestions of methods to correct (without buying a new fuel sender), or even determine the exact capacity of the tank?

Thanks

[fairdeal]

I would say its too much to expect a fuel gauge, made by one company, supplied with information from a sender made by a second company, installed in a tank made by a third company, to give "ideal" results.

That's the reality of boats.

But its certainly possible, assuming a "decent quality" gauge, and a "decent quality" sender,
to know fairly exactly, how much fuel you have - at least,

while the boat is in a "con*****ed condition" : motionless, in calm water.

The challenge will be figuring a way to "suck the tank empty". Easiest if you can rig up an external pump;
worst case you could - if your patience and hands hold out - empty it with the priming bulb.

Once you can't "suck" anymore out with the primer bulb, the tank is effectively empty;

anything still in there is useless to your engine.

Now, what does the gauge read? take a photo with your phone...

Now add exactly 5 gallons - what does it read now? take a photo

Add another 5 gallons.. et cetera......


here's part of my "photographic calibration chart" for my 130 gallon tank:

[Jason2tpa]

That's a good way to know the calibration, thanks. You're right though, tough part is getting the fuel out. IF the fuel gauge is wrong reading "E", yet fills full with 15 gallons, and its a 30 gallon tank, then theoretically there's 15 gallons in there....which equals a heck of a lot of siphoning lol. Plus thats about $40 worth of fuel I'd be wasting when a new fuel sender costs half as much.

I would say its too much to expect a fuel gauge, made by one company, supplied with information from a sender made by a second company, installed in a tank made by a third company, to give "ideal" results.

That's the reality of boats.

But its certainly possible, assuming a "decent quality" gauge, and a "decent quality" sender,
to know fairly exactly, how much fuel you have - at least,

while the boat is in a "con*****ed condition" : motionless, in calm water.

The challenge will be figuring a way to "suck the tank empty". Easiest if you can rig up an external pump;
worst case you could - if your patience and hands hold out - empty it with the priming bulb.

Once you can't "suck" anymore out with the primer bulb, the tank is effectively empty;

anything still in there is useless to your engine.

Now, what does the gauge read? take a photo with your phone...

Now add exactly 5 gallons - what does it read now? take a photo

Add another 5 gallons.. et cetera......


here's part of my "photographic calibration chart" for my 130 gallon tank:

[fairdeal]

That's a good way to know the calibration, thanks. You're right though, tough part is getting the fuel out. IF the fuel gauge is wrong reading "E", yet fills full with 15 gallons, and its a 30 gallon tank, then theoretically there's 15 gallons in there....which equals a heck of a lot of siphoning lol. Plus thats about $40 worth of fuel I'd be wasting when a new fuel sender costs half as much.

well, I certainly didn't "waste" the fuel when I emptied my tank; I had portable tanks available to hold it.

But as I said, above, simply installing a "new sender" might do nothing to improve your situation.