Gas Tank Venting

[Chooch]

My gas tank on my 73 Challenger is making noise, popping sound, when hot. Iam worried its not venting.  So I leave the gas cap barely on.  The gas cap is old school, not a modern venting type. Does anyone know anything about the venting process in this vehicle?  Thanks for everything, mike

[1 Wild R/T]

On the front upper area of the tank there should be four hoses, those connect to a small metal tank mounted on the shock crossmember... Another line attached to the tank & it goes to the engine compartment where it attaches to the charcoal canister.. Often the charcoal canister is gone & the line gets plugged... It needs to be open....  But also the small tank rusts out & the lines from the tank get plugged.. again they need to be open but they also need to run up as high as possible so fuel can't siphon through them... 

[crash340]

So, if the charcoal canister is removed and the pipe capped/plugged you must change the filler cap to a venting cap is that correct?

[dfrazz]

I don't mean to hijack your thread but currently I have my 4 vent holes capped and am curious if you can't just run the one line from the vapor separator to the filler neck like this.

[1 Wild R/T]

I don't mean to hijack your thread but currently I have my 4 vent holes capped and am curious if you can't just run the one line from the vapor separator to the filler neck like this.

Thats a 70 only 49 state filler neck, it uses a non-vented tank & cap, that vent line drops into the right frame rail.... If you sourced a 70 only 49 state filler & looped the vapor separator line back to it your have created a complex closed system with no venting....

[dfrazz]

Thats a 70 only 49 state filler neck, it uses a non-vented tank & cap, that vent line drops into the right frame rail.... If you sourced a 70 only 49 state filler & looped the vapor separator line back to it your have created a complex closed system with no venting....

So, if the charcoal canister is removed and the pipe capped/plugged you must change the filler cap to a venting cap is that correct?

If you did the 70's line from to the filler neck with a vented cap, would that be enough venting?  Also, do you need to do all 4 lines?  What if you attached 2 lines to a "T" or "Y" connection then to the line going to the filler neck with a vented cap?

[1 Wild R/T]

If you have the four lines capped I would run the 70 only 49 state filler & dump the vent line in the frame like the factory intended..

Or tie the four lines to the vapor separator that's supposed to mount in the trunk, then leave the fifth line (the one that should go forward to the charcoal canister) open..

[dfrazz]

If you have the four lines capped I would run the 70 only 49 state filler & dump the vent line in the frame like the factory intended..

Or tie the four lines to the vapor separator that's supposed to mount in the trunk, then leave the fifth line (the one that should go forward to the charcoal canister) open..

Is my vented gas cap enough or do I need run this line from the neck to the frame rail too?

[1 Wild R/T]

As far as I'm aware of the factory never ran just a vented cap so it may not be enough.. Then there's the fact allot of "vented" caps open allow air into the tank so the engine can draw fuel out of the tank without collapsing the tank (It can happen, I've seen tanks sucked in dramatically) but they don't allow air out like when on a warm day the fuel expands... So the tank pressurizes... Also when you try to fill an unvented tank with the new vapor recovery style pumps the pump can click off if you try to fill quickly...

All that said try it & see if it works for you...

[Chryco Psycho]

Under extreme situation you could use maybe 1/2 gallon in 11 seconds or so & wide open throttle even at that rate I doubt you create enough vacuum to collapse the tank , air can move through a vented cap relatively quickly

[1 Wild R/T]

Yeah if you reread my post you'll see I say the vented cap would prevent collapsing the tank but but allow air to escape...

[Chooch]

I checked the current system on my 73 Challenger pertaining to gas tank venting. I found out that the vapor separator has been removed and the 4 ports mounted on the front of the gas tank have been capped with rubber caps. So basically my gas tank is not vented and that's why it makes the popping sound when I drive it in hot weather. It also explains why its hard to get the gas cap off and when I do it makes a loud swishing sound.

I plan on placing a section of rubber gas line hose over one of the four tank outlets and running high and placing a fuel filter at the end and mounting it all to some place on the vehicle.  Does this sound like a good idea? Mike

[1 Wild R/T]

Should work..

[msbaugh]

Why over-complicate it?? Just take your regular, non-vented cap and drill a small hole in the middle. That's what I did!

[crash340]

just on tanks expanding and contracting in the heat etc, i had a car once that did that, nothing huge, take the cap off and you would get a small woosh, anyway, it had a small crease on the bottom of the tank, like a small dent, due to the tank expanding and contracting, like a coke can one day it just split open along the crease!