Which is better, a vented gas tank, or a vented gas cap? I'm getting ready to modify an unvented Mustang tank to fit into my Econoline. The original Econoline tank had a ~1/2" tube on top that vented the tank, but if I can use a vented cap instead it will one less thing to weld to the tank.
I had a lot of trouble with my tank after I got the car on the road. I vented it at the top near the filler but it was dificult to fill up because it wasn't venting at the tank. It literally took about a half an hour to get it filled if I didn't loosen the sending unit to vent it. There was a bung on the top of the tank that I had originally plugged. I ran a vent tube off of it and no more problems. I'm no rocket scientist but my guess is that too much air preasure would build up and cause the gas nozzle to kick off when I was putting gas.
I put a new tank in my Galaxie and it didn't have a vent built into it. I now wish I had welded a bung in the filler neck or near the top of the tank to vent it. I bought a "vented cap" from Napa that doesn't actually vent the tank. It has built up a ton of pressure a few times. I even drilled a small hole in the cap to help it vent, but the rubber rotates under the cap and seals it back up. I've resorted to installing the cap, but barely tightening it, hoping it will vent. Maybe I should just try a different cap... Malcolm
I put a bung type tank vent on my t-bucket. The tank is under the bed area, and the filler and neck come into a compartment in the bed. When I fill it up, it fills to the top of the filler neck and then proceeds to leak fuel until the neck is empty and the fuel level is lower than the vent. I am probably going to plug the vent and go with a vented cap.
I was wondering about that very thing, Briggs. The stock Econo tank has a elbow on top. I'm going to look in the manual to see if I can figure out where it was originally vented to, but I'm going to guess that the hose went up so that it would fill along with the filler neck and dump all that gas.
My falcon has a tank vent and a vented cap. Not sure exactly where the tank vent goes, haha. http://www.jalopyjournal.com/forum/picture.php?albumid=405&pictureid=16097 http://www.jalopyjournal.com/forum/picture.php?albumid=405&pictureid=16096 I'm planning on moving my gas filler into the trunk and changing to a non-vented cap. We'll see if anything changed after I do that. Norton
Speedway sells a right angle vent fitting that has a rollover valve in it. It's brass and has a ball in it for the valve, and a 5/16" nipple to attach a vent hose to. It threads into an NPT bung. I used one on a tank I made. I welded a bung into the top of the tank and the fitting just screws right in. I made a homemade brass thing that plugs up the end of the vent hose with a 3/32" hole drilled through it to keep dust and bugs from getting up inside the vent hose, and that seems to vent it fine.
clarence has similar issues. back when we used leaded gas i could just put the gas nozzle in the filler neck, click it up on high, walk away, and come back when it turned itself off. now i have to baby sit the nozzle the whole time. i have to hold it out to where it barely sticks into the filler neck and hold the handle to where it runs as slowly as possible (much slower than the slowest "click" setting). yeah, this has been going on for 15-20 years. i thought that the vent tube was clogged so i dismantled the whole shebang last year, cleaned, and reassembled. i was really bummed when it didn't help anything at all. i guess that unleaded gas bubbles up worse than leaded. so the next time i need to work on the fuel system for any reason i'm going to install a bung into the top of the tank with a bigger/additional vent tube. the only vent tube now is a steel tube about 3/8" i.d. that runs from the bottom of the filler tube to the top of the filler tube. that's confusing. it's parallel to the filler tube and attaches at both ends of the filler tube, but not into the tank itself.
Maybe I can scan my service manual. It shows the vent exiting the top of the tank and running parallel to the filler neck and then up past the filler about 6", then looping over and heading back down.
From what I have been told the "vented caps" only allow air to enter the tank....not escape. When you cars goes through a hot/cold cycle pressure builds up in the tank. I experience this on my '64 Tempest and it does not seem to be a problem.
How are you mounting the tank? Will it be inside with the fill outside? If you're doing it inside, you'll need a hose to vent the tank to the outside, not in the cabin.
Why would I vent it inside? The tank is mounted under the van and the stock vent followed the filler neck to the outside of the van and vented externally. None of it enters the cargo area at all (unlike the 61-64 Econos). Maybe that's what you're thinking of.
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