Re: Expanding Gas and/or Air? or What?
Is the fuel fill and vent both at the highest point of the tank where it was parked? If not what is to stop air from being trapped at the other end of the tank? Is the fuel vent at the top of the tank? Does the vent tube protrude down into the fuel when full? I had one tank which had the vent and fill tubes at one end, which in the way it was mounted ended up being half way rearward on that tank. If the tank was full, and the boat jacked up high in the bow, the vent which was about 4" rearward on the top of the tank would be blocked by the tank as the fuel sloshed back and found level. A rise in temp would expand the fuel, compressing trapped air which would then force it's way out of the tank by first pushing fuel up the vent or out the cap vents. The ticket was not to fill the tank that full, keeping the tank about 4" from the top was the key.
Since neither the fill or vent tubes protruded down into the tank at all, it was possible to fill that tank to the very top, even to fill the fill hose as well, when of which gas would find it's level at the same time in the vent tube. Which on this boat was a few inches below the filler port. (The filler port was on the top of the gunwale, the vent came out just below the rub rail up near the tank). If you filled the tank too far, it would pump gas right out the vent if the boat was level, worse yet, it would dump gas if you happened to have squeezed in every last drop while on the trailer,then launched the boat right away. It was a factory tank in a 20' Sea Ray. The vent in that boat was up front on the side of the bow, the filler was at about mid ship and ran forward about 8' along the gunwale and down to the tank below the deck.
