Hi Guys, I have excess amount gas fumes on my newly installed gas tank. looking for ways to route vent line on 56 f100. also Im reading on the internet that vent line should higher than filler neck?? Can some tell me why. I have about 3 inches from neck to planks of the bed of the truck. i have vent line out of the top off tank with hose running to side of tank about the height off the tank. any ideas locations for vent??
thanks Kenny

 

I am working on that one right now too. I thought I would run it up into the box channels on the bed sides but I have the roll over vent end from summit and it needs to sit the other way up so that didn't work for mine but it would have been well hidden. Now I'm thinking running it into the fender well area and making a little baffle thing for it to keep the dirt and water kicked off of the tire from getting around it.

 

Geooffthepiolt , my ideas are , 1 venting the hose back into cab , enclosed the original gas filller pipe end plumbing rubber cap with a nipple to reduce to 3/8 hose fitting. Using a 2 way gas venting gas cap. When neutral position is closed . 2nd idea is run the vent hose from tank to rear fender ,running up to highest point drilling a hole in towards the inside bed . Using a 45degree vent from a boat west marine store. Still on fence how to do this...

 

Gas tank needs two vents.
One is used when filling the gas tank to let the displaced air out.
Second is used when the engine is running to allow air into the tank to take up the space left by the gas being used.

First one is normally created by either a gas tank filler tube that is a wide open tube, much larger diameter than the nozzle at the gas station. Cars well up into the 1970s had them. Newer cars with the filler tube that has a hole only big enough for the fill nozzle use a separate 1/2" or so tube that is connected to the top of the tank and runs to the very top of the filler tube, above where you fill it. While the tank is being filled the air escapes out the top of the tank, through the 1/2" tube, and is vented from smaller holes that are around the filler tube hole.
Second vent for allowing air into the tank while the engine is running is normally either from a vented gas cap (non sealed fuel system) or an external vent. The external vent can be a simple 1/4" line from the top of the tank to a charcoal canister which will absorb the fumes. This vent does not have to be above the filler neck, the charcoal canister can be mounted where ever there is room. It has to be coming from the top of the tank to minimize the chance of liquid fuel getting in the line. Factory systems sometimes have a vapor separator unit but I have not needed one.
Where are the fumes coming from?
If this is a factory style system with a vented gas cap you should not need another vent. If you are using a sealed cap then you will need the vent and I would run your vent to a charcoal canister.
I run only sealed gas systems on my builds and have no issues with fumes in the garage.
With my fuel injected setups I use the factory purge solenoid to pump out the fumes from the charcoal canister into the engine as needed, but because of the way my latest computer was programmed that function was eliminated. I have a 1/4" vent line running into the charcoal canister with no pump out provision and I have no issues with gas fumes.
Early carb setups with the canister used a complicated vacuum system to pump out the canister, not easy to duplicate.

 

Hey Kenny,
I second Dave's suggestion to use a charcoal canister. My wife can detect gas fumes at microscopic levels.... I was taking a lot of incoming griping.
We use the rollover vent with a line over to a charcoal canister we got off of a minivan at a salvage place. (A new canister is ridiculously expensive... our's was $5).

Our under bed tank was making some odd whistling noises in the summer before we added the vent.

Good luck over there.

Ben in Austin
1950 F1

 

Here is another solution. If you use this you do not need a vented cap . . . which are getting harder to find anyhow:

Tip Valve for Tank Vent - AN8