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Like many of you I have a portable 6gallon fuel tank for my boat. I have the one with the vent screw on the cap. I always thought you unscrew the thingy on the cap and now it's venting. Close the little thingy and it is sealed.
Question is when I unscrew the thingy on the cap and start motoring around the lake my tank still seems not to vent. It will cavitate when there is no sun or ballon up when the sun it on it.
Is it a certain pressure that makes it vent or do I have a Monday made tank.
Sounds like you got some gunk getting in the way of the vent. You're right that the vent cap should be unscrewed to allow venting, and screwed down to seal it off.
I'm assuming it's a plastic tank, and not a brand new one ?? I'd take the whole gas tank cap off, and see if I could clean it ... or maybe take a air hose to it. Lots of dirt & debris can get sucked into the bilge area, while trailering a boat, and some of it could have ended up in the vent screw housing. Open bilge boats are the worst for this, but even those with a hatch/platform over them, have the air scoops to circulate air thru the closed system, and they can capture road dirt/film & debris. They can even stir up any dried up stuff, that may be in the bilge area. Ever wonder just how in the heck a bilge area (gas tanks/batteries/onboard charger) that's in a closed system, can get so dang dirty & funky .... LOL !! ... now you know.
If push comes to shove, and you have to replace the tank : BEFORE you hook it up and put gas/oil in it .... take a minute to run a vacuum line down inside it, and vacuum it out real good. Little pieces of plastic shavings can get inside, during the making process, and they can cause major problems. It may not be a bad idea to vacuum it out ... then tap around on the outsides (esp the top & corners) ... then vacuum again, just so you have a shot at knocking loose any shavings that might be out of reach of direct contact with the vacuum hose.
... cp
Thanks Pappy. I am going to get to the bottom of this tomorrow.
A good indication that the tank is not venting is the primer bulb will collapse.