Gas tank trouble

[383man]

Frank have you looked at a factory service manual to see just what your car used to vent from the factory ? I ask because some years did not leave room in the gas tank for fuel exspansion as some used a liquid vapor seperator that was not part of the tank but was in the trunk-1/4 panel area as it let the fuel go into it and then vented the fumes either to the eng crankcase or a charcoal canister. The fuel that was in liquid form the liquid vapor seperator drained back into the tank. Also I am guessing you have the right filler neck on the tank as the filler neck will stop venting when the full gets so high and cut the station pump off when filling the tank. Some cars do that so the tank has enough room for the fuel to exspand as thats why the filler necks have the smaller line on the side of them. If it had the wrong filler neck and did not shut the pump off at the right time it could fill the tank to full and leave no room for fuel exspansion. Ron

 

[Yatzee]

Any tank with vent outlets at the front of the tank should actually have the tubes internally run both to the rear of the tank and the front of the tank. This guaranties that any fuel in the vent lines do not experience internal fuel pressure and at least one of them is in open space (no fuel just air) internally. In many cases the two tubes were connected together at a high point, usually 8 - 10 inches or more above the top of the tank. Barring this arrangement a vent of at least 1/2 inch should be run from the top, front left side of the tank back to an inlet on the side of the fill tube just below the cap by an inch or so. With a rear fill tank, the 1/2 vents have to run from the rear top side of the tank to the front top side of the tank, looped 8 -10 inches higher than the tank and again 1/2 inch in diameter. This allows pressurized fuel at either end of the tank to flow to the void at the other end of the tank. Gravity and pressure determine weather the fuel actually flows over the top of the loop or not. Higher the loop the better. This occurs on acceleration, deceleration and when parked on a slant. One end of the tank will obviously be in an air space at the top of the tank that the vent tube can dump fuel back into from the pressurized tube end. The advantage of a larger tube is that it's harder and takes more pressure to push fuel up a larger diameter vent tube. 3/8 vents can be tried but will probably require looping at a higher point from the top of the tank, maybe as high as the underside of the package tray. This system requires the installation of vent nipples but remains a "closed" system with no odor venting or external dripping. As air enters the vent tube from one end or the other ( one end will always be in an air pocket within the tank ) the saturated end will drain back into the tank itself by gravity as air enters the tube from the vacant end. You will never be able to completely fill the vent with fuel - it will come out the filler tube first on over filling.