Fuel Overflowing Fill Tube But Cannot Pump Fuel Out.

Filled her up yesterday. 50 Gal. Stopped pumping at auto cut off. Today fuel is overflowing out of fill tube. Took cap off. Fuel is all the way to the top. So my first question is why is this happening? Temp yesterday was warm, today is cool. Both days boat was level.


So I pumped the fuel out of the fill tube. My transfer pump pickup want WAY down to where it sounded like it was rattling on the bottom of tank. I pumped about 1/2 gallon of fuel and then pump would not pick up any more. I have experienced this before with other pumps and siphons...........unable to siphon the gas, EXCEPT for gas in fill tube. My second question is why is this happening? My fill tube is a combination fill and vent. Could there be something wrong with it?


Thanks for any help.

Only one reason I know that would cause fuel in a tank to go against the law of gravity and that’s pressure....as in the tank is pressurizing. Check your vent line is clear.

ClassicAQ said:

Only one reason I know that would cause fuel in a tank to go against the law of gravity and that’s pressure....as in the tank is pressurizing. Check your vent line is clear.

Click to expand...

It turns out that these “problems” I’ve dealt with regularly over the last 10 years are NOT problems at all. There is nothing wrong with my boat’s fuel system or my transfer pump….only with my boat’s owner.

I realize now that I have overfilled the tank, and that overflow should be expected if filled to capacity. My 50 gal tank, if full, can expand by over a gallon’s volume in hot weather.

I realize now that the fill tube makes a 90 degree turn at the tank with a metal fitting, and that my transfer pump’s suction line fitting will not go through the turn. This is what my pump’s suction line fitting was rattling against…..not the innards of the tank. This is why I can only pump gas that is in the fill tube.

I know now that I’ve spent many frustrating hours dealing with problems that existed only in my mind. You would think a guy with 6 boats and 40 yrs of boating experience would know better.

CASE CLOSED