Gas tank venting

[hillsidehemi]

My next project on the 63 R1 is to remove the gas tank and replace all of the rubber fuel hose.  Trying to search tells me the line for the vent up the rear sail panel will be quite a challenge.  I also see that maybe the gas cap is not vented.  What is the reason I could not just cap off the vent hose at the tank and then use a vented gas cap?  Thanks

[mfg]

19 minutes ago, hillsidehemi said:

My next project on the 63 R1 is to remove the gas tank and replace all of the rubber fuel hose.  Trying to search tells me the line for the vent up the rear sail panel will be quite a challenge.  I also see that maybe the gas cap is not vented.  What is the reason I could not just cap off the vent hose at the tank and then use a vented gas cap?  Thanks

I'm pretty sure the original '63 gas cap was vented. 

[hillsidehemi]

1 hour ago, mfg said:

I'm pretty sure the original '63 gas cap was vented. 

You are probably right, I have not checked since the car is still in storage but I think I have found info on the forums that maybe they were not vented?  If the cap is vented why the need for the other vent line out of the tank?

[mfg]

5 hours ago, hillsidehemi said:

You are probably right, I have not checked since the car is still in storage but I think I have found info on the forums that maybe they were not vented?  If the cap is vented why the need for the other vent line out of the tank?

Good question!....could be the odd shape of the tank, or its high mounting position in the car.

[silverstude]

The gas cap is vented.   Lately there's been a lot of speculation about what that escape hose is/was for.  I've owned Avantis since the late 60's and the only purpose I have observed is that hose serves as an overflow for the tank, not a vent for the tank.  ( the extended section over the axle certainly might create a draw at road speed to evacuate fumes, but certainly would not have been a mandated usage then because EPA wasn't born yet) .   The Avanti tank filler is somewhat high on the body and there's a ~6"  connector hose which has 2 clamps that can likely allow fuel to seep by if it were contained in that section.   Fuel escaping the filler in that area will drain into the rear seat alcove  and cause fumes in the car.    

Automatic fuel nozzle shutoffs were few and far between when the Avanti was a new car, probably not even invented yet....   The only way you knew the tank was full was when  you watched and heard it come up in the filler tube.  Taking your mind off the task would often allow  it to slop out the filler  and ruined lacquer paint was a big issue then.   One owner came up with a rubberized bib that fit around the filler neck that stowed inside the gas filler door.  When you pulled into a station and proudly hopped out to fill your tank, opening the filler door would allow the bib to flop out like a large tongue and extend almost a foot down the fender.  It was certainly different, but helpful in  preventing paint problems.  So, the overflow tube allowed the excess fuel in the filler tube above the tank,  and probably a little more to exit out of the tank and flow out over the right rear axle tube.  

 The rubber should be replaced, since it's likely dry rotted.  Even if it isn't, todays ethanol fuel will do it in quickly.  Replacing the loop in the sail is not easy, but if you can thread a length of maleable wire ( rebar tie?) through the old one, you may be able to connect it to a length of new and pull it backwards through the sail, or even just push a decent length into the sail from one of the holes and allow it to naturally loop.  

 

Edited April 11, 2022 by silverstude

[hillsidehemi]

All good information here.  Today turned out to be a pretty good weather day so I went out to the garage and uncovered and moved things around to get to the Avanti.  This Avanti definitely had a non vented gas cap.  Who knows if it is original or not.  I removed the rear seat and took a look at the tank and lines.  No real signs of rot but the rubber lines probably are original.  I'm going to borrow a camera scope this weekend and see if any rust in the tank.  If so I will remove it and then deal with the rubber hoses then.  If I can I will try to fish a new one in there.  I am also going to add a vented cap and see how that works. 

As far as the vent hose being used as more of an expansion overflow, I'm skeptical.  Seems to me if gas was forced up into the vent hose it would also be forced up into the fill tube if a vented cap.  If a non vented cap I suppose the air pressure could not escape the fill and that might keep the gas from going into the fill hose. Then possibly the vent hose would work as described for expansion.   Liquid will seek the path of least resistance and if it can escape 2 ways it will balance itself.  Probably over thinking it and will just try to replace everything the way it is.  Thanks for the help.

[regnalbob]

 

10 hours ago, hillsidehemi said:

My next project on the 63 R1 is to remove the gas tank and replace all of the rubber fuel hose.  Trying to search tells me the line for the vent up the rear sail panel will be quite a challenge.  I also see that maybe the gas cap is not vented.  What is the reason I could not just cap off the vent hose at the tank and then use a vented gas cap?  Thanks

An original Avanti gas cap is not vented.

Edited April 12, 2022 by regnalbob
Added Photos

[brad]

Exactly, they were Non-Vented. The hose up into the sail panel and don again through the floor is the vent. 

[silverstude]

Ok, the cap wasn't vented.  The hose still poured out excess fuel from overfilling tho. 

[mfg]

35 minutes ago, brad said:

Exactly, they were Non-Vented. The hose up into the sail panel and don again through the floor is the vent. 

This 'old dog' just learned something!!....Thanks!

[Kodjo]

8 hours ago, silverstude said:

Ok, the cap wasn't vented.  The hose still poured out excess fuel from overfilling tho. 

I disagree as the top of the ventilation hose is much higher than the filler opening. So, the excess of fuel would pour out the filler opening. The hose is there for ventilation. Even the parts catalog states "0307-18 HOSE, gas tank vent".

[tanda62]

So on one of the original questions can the vent hose be capped if you use a vented gas cap?

[Rob Dudley]

I suspect if you were to park on an angle with the right side high and a full tank then fuel could be forced out the gas cap without the vent on the other side. 

[Gunslinger]

35 minutes ago, Rob Dudley said:

I suspect if you were to park on an angle with the right side high and a full tank then fuel could be forced out the gas cap without the vent on the other side. 

Been there...done that.  I learned the hard way never to completely fill an Avanti gas tank and park it driver side with any kind of down angle...especially on a hot day.