I have a gas fill in my driver side fender that has a seperate tube attached for the fill vent. I am thinking about changing to one of these that has no fill vent connection. Anyone know how to vent this or is there another way to vent the tank for filling?

 

If you supplied a picture of your existing vent it would help. But I'd think you could take your existing vent, route it to a high spot, put an inline gas filter on it to keep dust/bugs from entering the tank and then a drain hose towards the ground. Just one option I'd think. Mark

 

For tanks with a filler neck only and no vent tube I run one of these off a 3/8" nipple from either the filler tube or top of the gas tank. It is a one way check valve that lets air in but fumes cant get out, they were used on 1985-1995 camaros and firebirds. They may not be easy to find new but there should be plenty of those cars in the junkyards. There should be one way check valves available aftermarket as well or you could use a rollover valve which works the same way but may need to be mounted to the top of the tank. I woudlnt use a gas filter only because the gas fumes will always be dumping around the car.

 

The existing neck looks like this one.

 

Do the same darn thing, put a small fitting in the side of your new fill cap nipple or the hose right below the nipple portion and hook a vent hose to it. Lets not re-invent the wheel, the picture you posted could not make it any easier.

 

Hey Tom,
We went with a Rollover vent in the top of the tank running to
a charcoal canister to eliminate nasty venting odor in the garage.
My wife suggested this might be a good idea....


Ben in Austin
1950 F1

 

Tapping into the new setup would work only if the new cap was a "venting cap" vs sealed "non-venting". With the rubber seal shown in the picture, my guess the new flip top setup is not vented.
Mark

 

I have done it that way, and then put the check valve on the end of the hose. The idea is to let air into the tank but not let the gas fumes out.
Nobody wants a garage smelling like gas.


Tapping in below the cap will work with a non vented cap, the check valve allows air into the tank when the engine is running so no need for a vented cap. Venting is needed to do two things
- allows air out of the tank when filling so it doesnt back up and spit back (larger the vent hose the faster you can fill the tank)
-allows air into the tank when the engine is running so a vacuum isnt formed which wants to collapse the tank and shut off the fuel supply.
I have done it both ways, with a 3/8" vent hose tapped under the cap and with the larger 1/2" vent line to the tank depending on the tank design. In this case with that sealed cap the 3/8" hose tapped into the filler tube under the cap will allow air into the tank when the engine is running and the cap is sealed which will keep the tank from collapsing. The cap looks wide open so air will come in from the outside through the open cap when filling up.

The other picture of the filler with the 1/2" vent line is a "modern" sealed system piece and the vent normally connects to the top of the tank at the sending unit or a fitting on the tank. This allows air to excape the tank during fill up (modern small hole in the gas fill to keep fumes from excaping when getting gas). Air to the tank when the engine is running comes through a small vent line hooked to a charcoal canister.
Hope that wasnt too confusing, just have to remember there are actually two ways air has to get in and out of the tank. One for engine running and the other for when filling the tank.

As an example this is the gas tank in my 47 cadillac. You can see the port for the vent to hook up from the filler tube. This allows air to push to the top of the tank during fill up and vent out into the filler neck.
Air for engine running comes from a 1/4" line that connects to the charcoal canister through a check valve on the canister. If you dont run a canister the check valve would go on that line.




Older cars with the wide open gas filler tube didnt need this system, just a vented cap to let air in when the engine was running and air out of the tank when getting gas through the huge open gas fill tube. I prefer sealed systems and I type too much!

Both trucks I am building now will get the larger 1/2"' vent line to the tank and a 1/4" vent line through a charcoal canister.

 

There are so many options for venting that I'm not really sure what I need...

This is the tank that I installed:


It has a bung for venting but I assumed it would be for the fill vent but now I think its for the running vent???

The flip cap is vented. Does that mean I don't need another vent for running, just need one for filling?

 

if the cap is vented you only need the fill vent tube into the fill neck. Make sure the fill vent opening is slightly below the top of the tank so it spits back with a little air space still in the top of the tank. Otherwise if you shoud fill up on a cool AM/from cool underground tank and park in the hot midday sun the gas can expand and push past fuel pump/carb.

 

You don't have to have a fill vent, stock they did not have one. If the cap is vented that is all you need.

 

I think I get it now but of course, I have more questions.

Since the hole is in the top of the tank do I need one of these?
1948-79 Ford F-100 Rollover Vent Valve, In Tank, 1/4 Npt

I'm not sure how to add the filler vent to the fill tube. Can I just drill and tap a hole in the filler neck or do I use an hose adapter to connect the vent tube from the tank? Is 3/8" hose big enough for the vent?

 

If you are using a vented gas cap and a wide open filler neck (larger than the gas station filler nozzle) then there is nothing more you need.
The vented cap will allow air into the tank while the engine is running.
The large gas fill neck will allow air out of the tank while filling up.
Nothing else needed, if you were running a sealed gas cap you would need to do more work. You can cap off the other ports on the tank that you do not need.

 

Thanks guys. I will try it without the fill vent and see how it goes. I can always add it later if I need it.

 

Ben, could you share who's tank you are using? I'm in the market for one for my 49 F1. thanks!