Gas OVerflow problem 1988 20' searay i/o

[Bobbybones]

Gas is coming out of the vent hole on hot humid Mississippi days. If I unscrew the gas cap I get a hissing sound and then the leak stops. I initially thought I overfilled the gas tank which could still be the problem. Have been out on the boat on three short trips and the tank is showing between 3/4 to full still leaking. Any suggestions greatly appreciated.

Thanx
BB
View attachment gas overflow.bmp


You can see the gasoline stain around vent hole, the gas cap is directly above.

 

[jeeperman]

Re: Gas OVerflow problem 1988 20' searay i/o

Perhaps the vent line has a sag in it like the trap on a sink drain.
And your really seeing the "trapped" fuel (or even rain water) being pushed out.
But not enought to clear the trap totally.

 

[Bondo]

Re: Gas OVerflow problem 1988 20' searay i/o

Perhaps the vent line has a sag in it like the trap on a sink drain.
And your really seeing the "trapped" fuel (or even rain water) being pushed out.
But not enought to clear the trap totally.

Ayuh,... or it's on the Low end of the tank when parked where it is...

 

[BWT]

Re: Gas OVerflow problem 1988 20' searay i/o

I'm kinda thinking the same thing as Jeeperman. Check to see if the vent line has a loop or sags before it gets to the fitting on the hull. If gas is being pumped out then the line is allowing flow, and if you're getting a VERY slight hiss when opening the fuel cap then that would explain it. If the vent line is coiled it's acting as a trap (much like your kitchen sink). As pressure builds / expands when it get hot, it's the fuel in this coil that's being pushed out (but yet there's enough resistance because of this trapped fuel that it's allowing a small amount of pressure to build in the tank). I'm not a betting man, but suspect this is what you're going to find. Shorten the vent line so that it's as straight of a vertical run as possible and the problem should be solved.. Hope this helps!