Hi all, First off a big thanks. Through all the posts here, you have all helped my newbie self tremendously in getting my 53 chevy up and running. I'm now driving it daily and it's running great. One issue has come up, and as i've gathered from some of the posts here, it could be a dangerous one. I have replaced the entire fuel system and on the new gas tank, I noticed that after driving a bit, and then letting the truck sit, gas would puddle at the top of the tank around the fuel gauge sending unit. (It's a 54 unit, so it has the little tube coming off the top but the gas is run out of the bottom of the tank. The tube though has a proper copper fitting in it to plug it - sorry for my lack of proper terminology.) Initially I thought it was just not seal well, so I pulled it out and put silicone around the gasket and then reattatched. It still puddled after driving for a while and then leaving the truck. Another thing I noticed is that gas would pour out of the filler spout under the same conditions (driving for a while then letting it sit). The rubber seal in the gas cap was totally dry and cracked so I got a new gas cap. Now the new gas cap, under the same conditions, makes a whoosh noise when you take it off. I thought I must have gotten a non-vented gas cap, but check and it is definitely vented (so the autoparts store says based on their catalogue). Also, the gas is still puddling on the top of the tank, but not nearly as much. Any thoughts? Is the puddling from fumes or from actual gas leak? And the only thing I haven't replaced is the tubing that goes from the tank to the filler spout nor the filler spout itself. Thanks!
Whatever it is, it's dangerous as hell. Fix it immediately. Sounds like for some reason, your tank is NOT venting properly. Are you sure you have the proper cap for the filler? Get new filler to tank rubber hoses (the short ones-two different sizes). Pull out the filler tube and check for blockages in both tubes. Get a new sending unit gasket. They are cheap. Silicone is not meant for being in contact with fuel. However, it's probably the cap. You probably have a non-venting cap on the filler. Andy
fuel I was going to say that the tank is getting a vacuum after driving which normally leads to a whoosh as you open the cap, a pressure build up normally makes a hiss and you can feel the cap being pushed off the neck. but the fuel around the sender leads me to believe its pressure build up and its being released at the weakest point of the tank, the gasket, your cap is not venting for one reason or another and along with this you should check the filler hoses have not collapsed inside causing a blockage (unlikely but possible) i would try driving round without the seal on the cap (normally easy to pry out) on a cool day and see if you still have the problem. (silicone just turns to a slippery jelly when exposed to fuel so best to use a sealant specified as safe for fuel)
The silicone I used was a fuel specific silicone. The leak there seems to be from gas condensing on the spout off the top of the unit. I notice a droplet there almost every time I drive. I checked the cap and it is definitely venting. I'll replace the hoses tomorrow and see what shape they are in. Can anyone explain to me how the gas pressure and vacuum issues work? I can understand that as gas is used, air needs to replace the volume of gas and if it can't, a vacuum is created. But how does pressure build up happen? And is there any easy way to see which one I'm dealing with? Thanks.
Pv=nrt Physics teaches us that! First time i've used my formal education in over 32 years Basically what that means is that liquid turns to a gaseous form when pressure and temperature increase. When gasoline gets hot it has a tendency to turn into a gaseous state. The molecules expand and as they do, the pressure on a vessel holding it increases. As the pressure increases, so does the amount of space as takes to hold the expanding volume. The gaseous vapor is going to find a way to "vent" itself to relieve the pressure. That is going to be at the place of least resistance. Most times, it will be a vented cap. If the cap is not vented, it will find the weakest part of of the vessel, normally the sending unit, and try to equalize the pressure. When that occurs, the cooling effect of it will cause condensation, or in other words, a re-liquification of the gaseous state, into gas. My head hurts now, because I actually used my brain for something other than bein a wise-acker! Hope this helps.
You ' Checked It ' ? But it's obviously not venting else you'd not have the leak nor the whoosh.... Better get this fixed (drill a single 3/16" hole right through the middle of the cap for now) before it explodes and really spoils your day .
So I checked the filler spout hoses and they were fine. I tightened the copper fitting and added Teflon tape around the threads for a better seal. I also drilled 5 1/16" holes in my old cap. I was worried about one big hole letting water into the tank if it rains. It definitely changed how easy it was for air to pass through the cap. Seems to be working for now. This isn't a long term solution though. Any suggestions for adding that type of ventilation without having holes in my gas cap?
Buy the lockable cap from our vendor. It vents and the price of gas is going a lot higher than it was last year. Soon crooks will learn to syphon gas.
