I need to vent................

[mobileortho]

Or do I? I'm trying to determine if I need to run a vent line to my underbed tank. I went with the bed fill spout and the illustrations I've seen show the spout attached directly to the tank via a short hose, but there is no provision on the spout itself for the vent as it is on the stock unit. Is there another way to run a vent line or is it really necessary? There is also an additional outlet on the opposite side of the tank that I don't know what its used for. Someone suggested that it was there to relieve pressure buildup, but how do you go about doing that?

[CAL 58 GMC]

You definitely need to run a vent line. It's like drinking out of a plastic water bottle with your mouth sealed around the rim as you suck water into your mouth, the bottle starts to collapse and water gets harder to suck out. The fuel will flow alot better with a vent.

[OrrieG]

If you are running conventional carb with stock engine mounted fuel pump you need a vent. Like Cal said without it and an unvented cap you get a vaccum in the tank. Also no pressure relief when filling. I don't know anything about modern injected engines with the fuel pumps in the engines. My after market tank came with a threaded hole for attaching a 3/8" hose fitting. I a using the stock filler relocated to the bed side so that is where the vent will go. You can get aftermarket fillers from marine suppliers that have the vent line configuration too. Some guys just run the hose higher than the tank and put in a check valve. Search some of the build threads using "gas tank" as a search word and you will find an bunch of different ideas with manf. info or links to suppliers.

[mobileortho]

OK, I think I figured it out. I found this vent tube off of a late model fuel spout. It has a a cap on the end that allows pressure to bleed off as needed. Is it ok for me to mount it on the spout as shown and run the other end to the opposite side of the tank?

[Atomsplitter]

My motor is fuel injected and has a return line but I vented it anyway. I ran my vent line up the inside of the rear fender about a foot and back down. This was my only choice as my tank sits alot higher than yours and I wanted the vent well above the full level in the tank, where did you get the "one way" vent fitting from?

[entourageguy]

I've seen the one way fitting from compa ies like russell that make the an type fittings.

[mobileortho]

Originally Posted by Atomsplitter

where did you get the "one way" vent fitting from?

I believe it came off of a late model chevy truck. I picked it up at a local body shop that was about to trash it.

[mr48chev]

I'd run a vent similar to what Atomsplitter said he has on his truck. You might run a line over to one of the posts(bed corners) and run it up inside it with some type of vent cap on it. Out of the way and high enough so that it wouldn't bleed over if the fuel expanded in the tank on a hot day.
It's not rocket science, you just need to be able to vent the tank and have the vent high enough so that you don't create a leak when the tank is full.

[mobileortho]

I talked to the guys at Tanks Inc. and they suggested that I use this rollover vent valve. It will vent the tank and also seal itself off in case of a rollever. I mounted it in the right rear stake pocket, ran the hose through the frame then to the tank. I'm not sure if moisture will be able to get in so I'll eventually get some covers for the opening.