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'63 Avanti fuel tank vent tube issue


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Hello all. I recently had to replace my Avanti's fuel tank vent tube because I could smell gas coming out of the pores of the rubber. I believe it was original to the car. Certainly the sending unit was, which I replaced, and its gasket was nearly dust. However after all this I was still getting a strong gas odor from the car. I crawled around sniffing everything I could find and discovered that the smell was most notably coming from the end of the vent tube under the car!

I thought that since gas fumes are heavier than air that the figure 8 arrangement would have kept gas fumes from exiting the hose. I would have liked to have run the hose up in the c-pillar like the factory one, but there is no practical way to access that area. As a test I used a piece of a Home Depot bag and a rubber band to cap off the bottom of the hose, and the next day the gas smell in my shop was almost gone! But obviously that isn't a solution...so what is?

p.s. I am using a new Avanti fuel cap, I think I had bought it from Studebaker Intl but it's been 6-7 years. If memory serves it is a vented cap.


 

21,04-28, new fuel tank vent tube (2)_72.jpg

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The vent originally connected to a hard line, then the rubber line went up into the 1/4 panel, and was secured by a riveted on clip. then it went back down to the hole in the floor. That way it's up high enough that no amount of fuel sloshing would cause the vent line to fill up with fuel. 

Also, check the fill tube large hose, they can hide cracks behind that are not visible unless you take it out. If you do, pay attention to the clocking of the fuel cap, so when tight the ear doesn't hit the filler door when it's closed. Also check the solder joints on both the return line and the vent line on the top of the tank. A poor trunk gasket, and also exhaust deflectors that have slots in the clamp end can all contribute to fumes.

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I agree with Bez and add the following; The idea of a vent tube is to let the fumes escape and to let air in as you use fuel. It doesn't matter what bends you put in it. It should exit outside of the car.

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4 hours ago, brad said:

The vent originally connected to a hard line, then the rubber line went up into the 1/4 panel, and was secured by a riveted on clip. then it went back down to the hole in the floor. That way it's up high enough that no amount of fuel sloshing would cause the vent line to fill up with fuel. 

Also, check the fill tube large hose, they can hide cracks behind that are not visible unless you take it out. If you do, pay attention to the clocking of the fuel cap, so when tight the ear doesn't hit the filler door when it's closed. Also check the solder joints on both the return line and the vent line on the top of the tank. A poor trunk gasket, and also exhaust deflectors that have slots in the clamp end can all contribute to fumes.

I doubt I have fuel inside the hose, the engine has not been turned over since I started to fix the gas smell issue. The figure 8 arrangement was partly because I didn't know if it would be a permanent solution so I didn't want to cut the line shorter than might be needed, and also because the figure 8 would keep the hose longitudinally stable during driving - relevant since it wouldn't be stabilized by going into the c pillar area like the stock one.

Sending unit was replaced and is sealing well. The filler neck doesn't smell at all and is not sweating. The tank's solder joints are solid.

There is no large hole for the original vent tube to go up into the c pillar area, there are two small holes each barely large enough to accommodate the Studebaker hose. As I mentioned in my OP, I would have replaced the hose exactly if it were possible, but currently I don't see a way to do that. Open to ideas...pictures would be even better.

The gas smell is definitely coming out of the vent tube. And I confirmed this by temporarily plugging it. What I would like to know is: WHY? The vapor, which is heavier than air, would have to travel up the new hose twice before falling down and exiting outside the car. And I cannot have fuel vapor leaking out making my warehouse stink. It's chemically bad for all plastics, and a potential fire hazard.

As for letting fumes escape, since I have a vented gas cap would that not also allow equalization of air pressure? So why have a second vent (tube) if the gas cap is already vented?
 

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You might want to consider making a charcoal canister for the vent hose. I have had the same issue over the years with a variety of cars that vented into the open air and it resolved the issue.

Bob Caser

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Posted (edited)
On 5/8/2021 at 5:21 PM, bob caser said:

You might want to consider making a charcoal canister for the vent hose. I have had the same issue over the years with a variety of cars that vented into the open air and it resolved the issue.

Bob Caser

Got a link to one I could buy that would fit the hose?

 

Or...what about using a check ball valve like this one?

https://www.amazon.com/gp/product/B08PSYF3GZ/ref=ox_sc_saved_title_1?smid=A1THAZDOWP300U&psc=1

Edited by Palantirion
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Posted (edited)

*SOLVED*  😣

21,05-12, vent tube on coat hook_72.jpg

 

Using a Dremel I was able to cut out the panel between the two holes for the OEM vent tube, and eventually (rotating locking pliers against the panel for torque) I removed the hidden length of the original tube. It was nearly 2' long! Unfortunately I can't simply push the new tube up the gap because there is a second plate behind the panel I just cut, between the two holes. I can't see it, because of the tiny space, but I think it's fiberglass. I also am not sure if I should cut it - but it will be much more difficult because of the size of my cutoff wheel and the tight space. I was thinking of maybe trying to use thick armature wire as a guide to maybe force the new hose into turning inside the panel so I can run it like the stock hose. Does anyone know a good trick to make a rubber hose turn 180 degrees in a blind inaccessible cavity?

 

p.s. My gas cap is not vented, I checked: Blew into the vent tube with the cap on - blew gas vapor back at me. With the cap off it did not.

Edited by Palantirion
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If you remove the right rear window, you can peel back the unpholstery, reach into the C pillar and deal with the 2' loop. It's tight, but doable and with all 2' of new hose up in there, no gas smell.  Add rollover vents, etc. under the car as you wish!

 

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  • 2 weeks later...

For those (like me most of the time) that think kids these days don't care about working on cars...well, most of the time they'd be right. But there are exceptions: A front desk kid at a local BMW shop (where I was having some other work done) suggested that I drill a hole through the tube and use string to guide it around the internals. He was on to something. I ended up having to use a long twist tie to curve around whatever is inside that panel and then used that to pull the string which then pulled the tube successfully through both holes! It took a bit of futzing to get the right degree of tension on the tube to make it line up and pass through the 2nd hole, but overall it was not a nightmare. Kudos to those of the new car guy generation.

 

21,05-26, vent tube threaded_72.jpg

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  • 4 weeks later...

Aaaaaand we're back. I ran the new vent tube through the same hole as the original. The gas smell never quite went away. First I thought to blow out my shop to ensure no previous vapor was hanging around. Then I thought maybe there was something within the fuel system that might change after the car was run so I took it to a local show and back. I had it on my rack today after noticing the faint smell of gas vapor and vapor is definitely being pushed out through the vent tube. There was no dripping that I could see, but there is enough vapor to build up to visible moisture. Why is this happening?

12155126_2106-18fuelvaporoutvent_72.thumb.jpg.d36f3de2adf6e40cdaecb0d1495187e4.jpg

 

I am considering using a 1-way ball check valve to prevent gas from escaping the vent tube while still allowing it to draw in air. But I wonder if there might be any negative consequences if the tank can't push vapor pressure out (except through the fuel lines) if it's outside on a hot day.

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You have to allow for expansion with an increase in temperature.  The car does not have a closed system, like a modern car.  Unless you do a complete conversion on your car, you should live with the small amount of vapors from the system.  The vent should work in both directions.   

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4 hours ago, studegary said:

You have to allow for expansion with an increase in temperature.  The car does not have a closed system, like a modern car.  Unless you do a complete conversion on your car, you should live with the small amount of vapors from the system.  The vent should work in both directions.   

- I had thought about that, but two points that puzzle me: 
1) The car is kept in a air conditioned warehouse (max 75F) and yet the vent still expels fuel vapor. The only differential would be from the temp dropping at night, rarely below 60F.
2) The car did not used to make gas smell. Not until the original vent tube started weeping fuel, which was then smelling inside the car. I was not getting fuel vapor from the original vent tube with the car in the same condition and space.

Come to think of it, I didn't get any fuel vapor smell even year ago when the car was in a garage with a much wider temperature swing.

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If you have not buttoned up the back area, suggest you cap off the fuel vent tube by the sender, find a non-vented gas cap and give it a day at the constant 75 degrees in the warehouse. If no smell, go back to vented gas cap, run the gas vent hose as you did out the quarter window, up to top of roof and back to middle wheel. Let stand for a day again. It's detective work for sure.

Goal is to be certain 1) nothing else is leaking, and 2) you got high enough with that vent hose. There are actually four fiberglass holes that have to be passed through to get that vent hose all the way to the roof.

 

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Posted (edited)
3 hours ago, Ntenna said:

If you have not buttoned up the back area, suggest you cap off the fuel vent tube by the sender, find a non-vented gas cap and give it a day at the constant 75 degrees in the warehouse. If no smell, go back to vented gas cap, run the gas vent hose as you did out the quarter window, up to top of roof and back to middle wheel. Let stand for a day again. It's detective work for sure.

Goal is to be certain 1) nothing else is leaking, and 2) you got high enough with that vent hose. There are actually four fiberglass holes that have to be passed through to get that vent hose all the way to the roof.

- I buttoned the back up because of a show, but it's easy enough to pull the rear seat and bulkhead again. I like your idea for diagnosing. I do NOT like that you said there are 4 holes that the hose needs to pass through...makes me wonder how high the other two are and if my hose went up to that area and then got turned around a few inches too low. You wouldn't by chance have a picture or diagram of the layout would you?

FYI, I did try something a couple weeks ago...I removed my (non-vented) gas cap and then blew through the vent tube to clear any vapor, then I left the cap off overnight. The next day my warehouse stunk SO much more than before. And that confused me because the vapor shouldn't be able to push up through the filler neck, right?

Edited by Palantirion
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2 hours ago, studegary said:

Why wouldn't the vapor be able to come out of the filler neck?

- According to what I have read (and experienced) gas vapor is heavier than air. Thus is could not go up the filler neck unless the tank experienced pressurization.

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By the same logic, if the top of the loop in the vent line is well above the tank top, why would the fumes go up and out the vent line?

Edited by Avanti83
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7 hours ago, Avanti83 said:

By the same logic, if the top of the loop in the vent line is well above the tank top, why would the fumes go up and out the vent line?

- Exactly! It would have to be positive pressure. The vent line's primary purpose is to allow air into the tank to fill the displacement of fuel leaving the tank.

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8 hours ago, Palantirion said:

- Exactly! It would have to be positive pressure. The vent line's primary purpose is to allow air into the tank to fill the displacement of fuel leaving the tank.

It also adjusts for volume changes in the tank due to temperature change of the fuel and volume change when filling the tank.   

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The second pair of holes is about 2” above the lower pair. I could be wrong, but I think the idea was to get the top curve in the vent hose well above the filler neck.

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Posted (edited)
6 hours ago, Ntenna said:

The second pair of holes is about 2” above the lower pair. I could be wrong, but I think the idea was to get the top curve in the vent hose well above the filler neck.

- Because of the tight space I was working in I never got a picture of what was up inside the two lower holes. But I could feel with my finger something like a plate a couple inches above the holes. It felt like a small plate, I didn't feel holes, and now I wonder about "running changes". Regardless, I had to bend my wire-string-hose apparatus over that plate because it wouldn't bend under it. And, from the length of the hose I pushed up into that space I'm sure it's plenty high.

p.s. I have a borescope. I remember this now. Would have been nice to have remembered it then.

Edited by Palantirion
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When you said you went through the holes, I was assuming you ran it all the way up into the 1/4 panel like was original. When they built the car, they ran the vent up into the 1/4 panel, and looped it over a clip to about 4" from the TOP OF THE ROOF !  Then they glued the outside skin on. 

 

Edited by brad
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5 hours ago, brad said:

When you said you went through the holes, I was assuming you ran it all the way up into the 1/4 panel like was original. When they built the car, they ran the vent up into the 1/4 panel, and looped it over a clip to about 4" from the TOP OF THE ROOF !  Then they glued the outside skin on. 

 

- Not having x-ray vision I cannot confirm exactly how the hose ran within the c pillar. But once I got it bent back through both holes I fed it evenly so that all the length from my first page pics was up in the c pillar - save for the 2-3' needed to go from the c pillar through the floor. 
http://aoai.org/forums/uploads/monthly_2021_05/1784714215_2104-28newfueltankventtube(2)_72.jpg.856ef74392fbde9538dd37205c45e5e1.jpg
http://aoai.org/forums/uploads/monthly_2021_05/479298818_2105-12venttubeoncoathook_72.thumb.jpg.72cefee94d7c093fae5844f88a9161fb.jpg

I felt no resistance while feeding the hose up, didn't hit anything like a clip or snag, so I am fairly confident that it stayed vertical. But I can't know for sure. I was thinking that maybe it is possible that another 2-3' (which I could add with a barb fitting) might help push the peak of the hose higher. But without being able to mechanically secure it within the c pillar it might also make it more prone to bending which might defeat the purpose. Going from my memory of removing the old hose I believe my replacement is actually a little bit longer.

What puzzles me is why, with the car just sitting and the warehouse kept at 75F (+/-2), there is still pressure being build up within the tank. Can someone explain why this would occur? AND why it didn't occur prior to me opening the tank to replace the sending unit and the vent hose. 

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You can remove the quarter window, lift the upholstery and look up into the C-pillar area. You will see where the hose has gone. First time I tried this the hose bent forward and went into the area between the channels. I can't see how the sender is leaking much even if the electric feed-thru was slightly loose, but also check that the gasket is fully seated. Best I can offer is the old-school cause and effect. If It didn't vent fumes before look at each change made and see what effect from it could cause the fumes. There is an answer somewhere! Good luck with this....

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