Gas Tank Size

[amateurfishing]

To make a very long story short, i bought a used boat very late last fall with no real change to get it in the water for any testing. It was July this year b4 i got the motor working properly. Previous owner told me 1984 16 ft crestliner nordic explorer had 18 gal gas tank (it is under the floor). I put 5 fresh gallons in July and went out 4 times. Went to put 5 more in this am (with fuel stabilizer and fresh oil for winterizing) and could not get all 5 gallons in, overflow hole on outside of boat let a bunch out. So i could only put in max 10 gallons, have no way of knowing how big it really is cause fuel gauge not working. Is there any way to figure it out other than fixing fuel gauge? (hoping to fix that next year)

[hydro]

Siphon the gas out and count how many gallons you wind up with.

[BartmanMN]

The 18ft nodic has an 18 gallon. Not sure if the 16ft has the same or not.

[amateurfishing]

thx for the replys, previous owner told me he always put 2 6-gal tanks in at a time and never had problem: question--could it have been because it was on a sloped driveway at the time? and if that is the case, if i would fill it up completely full wouldn't I lose gas from bumps on the road or wavy water if it comes out that easy from the overflow? why would fuel spill out even if the tank is not completely full? Does trying to fill it up on a sloped driveway have anything to do with it?

[Down Deep]

The tank is under floor so unscrew the floor planel and see how big the tank is.

[amateurfishing]

k, so after mega freaking out for a week, previous owner had an "a haa" moment and told me there was a special pull nob on panel, so i got battery out this am, hooked all up, low & behold its for the fuel gauge which states 3/4 full in current position. its weird that its not automatically wired to motor though IMO. would b nice to lift up floor panel and actually see the tank, but im really new at this boat stuff and very mecanically illiterate, plus with 3 kids under 8, i rarely get time to myself that a child would not interrupt me, BTW how difficult would it be to lift floor panel out? big problem is that side console would have to be undone as well.