4 winns gas tank venting

[VMAX]

Hi guys,<br />It's my first time back on the forum this year, and I need some help.<br />Last year, I bought a 4 winns 170 horizon 3.0 liter. It's been a good little boat, except for one problem. When I fill the gas tank after a day of boating, and then park at home, everything is fine. The next day, when the sun comes out and heats things up a bit, fuel spews forcefully out of the vent. The vent hose enters the tank below the level of the fuel when full. This can be very dangerous. Now that I'm thinking about it, my other boat, a Hustler did the same thing last year.<br />Both boats have the same type of metal screw-in filler caps with o-ring seals on them.<br />It seems that the vent hose must have a pressure-relief valve in it? or something, since a fair amount of pressure builds in the tank before she blows.<br />Just for the heck of it, I tried leaving the filler cap slightly loose, and the problem seems to be under control now.<br />Is it possible that the boat should have a vented cap instead of a sealed one, or am I missing something obvious? Please help!<br />John

 

[DJ]

Re: 4 winns gas tank venting

VMAX,<br /><br />Are you sure you do not have a bow in the vent line. If so, it will trap air.<br /><br />Your only solution is to fill the tank only to the vent outlet. You should not be packing the filler neck full.<br /><br />The fuel cap cannot be vented.

 

[VMAX]

Re: 4 winns gas tank venting

C'mon guys, you mean to tell me that out of two boats that I own, two of them spray fuel out the vent when parked, but nobody else has run into this problem? I must have really bad luck. Let me know what you think,<br />John

 

[Mikedg]

Re: 4 winns gas tank venting

Over filling is the problem. I filled my boat to the brim in the cool of last fall for winter storage. This spring as the temperature came up the both tanks started spilling gas from the vents due to expansion. I had to syphon off some gas to stop it. It is amazing how much gas will expand on a warm day. The only cure is to not over fill the tank, leaving room for expansion.

 

[DJ]

Re: 4 winns gas tank venting

VMAX,<br /><br />The same principles apply to a car. However, a boat is a bit different.<br /><br />On a car, the pressure is vented through the charcoal canister system. "Packing" the fuel system in a car causes running problems. <br /><br />A boat is a huge heat sink, especially with a cover on it. The amount of "engineering" that goes into a boat fuel system is miniscule compared to autos.<br /><br />Also, fuel types can make a difference. Fuels high in MTB or alcohol content expand at different rates.