I just converted to the mustang gas tank in my 55 F-100, as you probably already know there isn't a vent hose inthe tank, the cap I have is vented which I think it allows air to scape when you turn it before opening it. Should there be a vent hose in the tank will it damage anything if I don't have a return line or vent?
Jaye

 

If you have a carbuerated engine the cap will need to be vented. I have the Mustang tank and installed a vapor recovery fitting for the fuel injected 5.0. In this case the cap is not vented so the vapor recovery system will capture all the vapors.

 

When caps are vented does this allows air to escape while the cap is closed or does the air escape just prior to opening the cap. Could I weld a pipe on the filler neck for air to escape?
Thanks
Jaye.

 

the vented cap allows air to enter the tank, so it doesn't create a vacuum in the tank, if it wasn't vented you would create enough of a vacuum that the fuel pump wouldn't be able to pull fuel

 

That's what I did with my original tank. I'm using a non-vented cap and slipped a piece of rubber hose over the pipe and routed it through the floor in the cab corner to keep fumes out of the cab.

Vern

 

Bememe,
Do you need the smog pump for the vapour recovery to work?
I deleted my smog pump but have a gas fume problem around my truck as I vented the tank out the back of my cab wall.
I scrounged some charcoal filters from the scrap yard and was thinking of using them and wondered about somehow returning it to the air intake.
Is this possible, safe and would it solve my gas fumes problem?
Anyone know?
GW

 

There is no need to vent the tank if you use a vented cap. as was stated the cap has a one way valve which allows air INTO the tank to replace the fuel as it is used. An open air vent allows gas fumes to EXIT the tank, a potentially unsafe condition, plus you are evaporating the "lights" in the fuel, an important component in the combustion process. Also you are allowing air to enter the tank at will, not just when the engine is running which can lead to condensation in the tank. Bottom line: DON'T open air vent your tank, especially if you garage your truck! Some (most) tanks will require a vent for filling purposes, but that vent should be piped back into the filler neck above the pump nozzle end when filling the tank and becomes a closed loop when the cap is replaced.

 

This may help. Copied it from a "know your car" website.

Gasoline evaporates quite easily. In the past these evaporative emissions were vented into the atmosphere. 20% of all HC emissions from the automobile are from the gas tank. In 1970 legislation was passed, prohibiting venting of gas tank fumes into the atmosphere. An evaporative control system was developed to eliminate this source of pollution. The function of the fuel evaporative control system is to trap and store evaporative emissions from the gas tank and carburetor. A charcoal canister is used to trap the fuel vapors. The fuel vapors adhere to the charcoal, until the engine is started, and engine vacuum can be used to draw the vapors into the engine, so that they can be burned along with the fuel/air mixture. This system requires the use of a sealed gas tank filler cap. This cap is so important to the operation of the system, that a test of the cap is now being integrated into many state emission inspection programs. Pre-1970 cars released fuel vapors into the atmosphere through the use of a vented gas cap. Today with the use of sealed caps, redesigned gas tanks are used. The tank has to have the space for the vapors to collect so that they can then be vented to the charcoal canister. A purge valve is used to control the vapor flow into the engine. The purge valve is operated by engine vacuum. One common problem with this system is that the purge valve goes bad and engine vacuum draws fuel directly into the intake system. This enriches the fuel mixture and will foul the spark plugs. Most charcoal canisters have a filter that should be replaced periodically. This system should be checked when fuel mileage drops.

My 54 Merc car with the original fuel tank has a vented cap with a steel tube that vents to the atmosphere.

The new tank I bought from No Limit for my 56 F100 has a fitting at the top of the tank with a long hose and it also vents to the atmosphere.

Chuck

 

OK. So I'm doing something dangerous and harmful to the environment...don't want to do that!
I have an unvented Hagens cap and filler door + neck. When I first started running the truck, I had a problem with the warm fuel returning from the Fuel Rails [I'm running a 5.0L Fuel injected engine with twined stock tanks on my '53].
The pressure got so much with a full tank and the heat that fuel came spewing out the vent! Running a tube through the top of the Filler cap has releived the pressure but now I've got the fumes and evaporation!

I have some charcoal filters, but how do I route the vent tube back to the engine...safely and economically?

GW

 

Thanks for all the advice I went to Advance today and they had a vented cap for a 56 F100 which is what I got the gas filler off of.
Jaye