Gas cap venting?

[alfabits]

Hi, I noticed when removing my gas cap on my newly restored Giulietta, a air hissing sound. Sounds like a vacuum noise. My gas cap has no breather hole. The cap came with the disassembled car so there's no way to know if it is correct. Should I have a vented cap? Is this a standard cap I could purchase from Moss motors?

This is the last time I ever restore any vehicle that wasn't running when I got it!

Any info on this matter would be appreciated.

[Gordon Raymond]

George,
The venting is supposed to be taken care of by the overflow line in the metal section that drains under the trunk. The old spiders were not meant to have either a positive or negative pressure in the tank. Thus, no vented cap. With modern fuels with iso propane and other added gasses, modern fuels are more prone to vaporize and stink up your car, with the factory overflow system. Yours may have been blocked, plugged or otherwise altered to decrease fumes. If you need photos of the correct vented system, let me know and I will post them for you. In another thread, "mud dauber" wasps were the cause of a plugged vent! Gordon Raymond

[alfabits]

H Gorgon. Actually the vents are open fine. I had the tank out again yesterday to fix a small leak coming from the vent tube where it comes out of the tank. I had to re-solder around the tube. I checked all the openings with air and filled the tank with water to remove all fumes before soldering. I don't understand how the vent works. It doesnt vent to the outside. It appears to only acts as a loop within the system. If you don't vent to the outside and you remove fluid (volume) then you will create a vacuum.

George

[Collivanfan]

George,
The pipe between left side of the tank & filler neck is, as you deduced, merely a breather to facilitate filling the tank.
A vented type cap should be used. The breather hole is often hidden under the cap & is virtually invisible.
Hope that this is of some help.
Tony
England

[Gordon Raymond]

Hi George,
By whatever name, Pn 1365.85.063, a metal tube, not all of it shown in the parts book, leads under the trunk floor, and is supposed to be open at the end to prevent tank overfill. As such, the tank and filler are not sealed by virtue of this "breather pipe" as referred to in the parts book. Not to disagree with Tony, but the main "breather" for this system is this pipe. I will send photo's of the correct tank cap, and this plumbing later today. This is not supposed to be a sealed system. Any pressure or vacuum when opening the cap, is a sign that your system has somehow become sealed. I will send you some close up's of the OEM cap from my totally original spider, with the other photo's later today. Gordon Raymond

[alfabits]

Quote:

Originally Posted by Collivanfan George, The pipe between left side of the tank & filler neck is, as you deduced, merely a breather to facilitate filling the tank. A vented type cap should be used. The breather hole is often hidden under the cap & is virtually invisible. Hope that this is of some help. Tony England

[alfabits]

Quote:

Originally Posted by Gordon Raymond I will send you some close up's of the OEM cap from my totally original spider, with the other photo's later today. Gordon Raymond

[101/105guy]

I too would love to see a pic of the 'vent pipe' with an opening to the atmosphere!
Gordon, does your '65 have this??
On my '65, tyhe tube just vents air from the front of the tank to the filler neck.

[Gordon Raymond]

Hi George, Hi Tony, Hi 101 /105 guy,
Let me start by saying I must be suffering mind melt down. TONY IS 100% correct. 43 years working on these things and I should read more carefully, not trust opinions possibly gathered from other Alfa's, and not trusted the Alfa parts book. Here are a series of photo's of the #1365.85.063 "breather pipe" in it's entire glory, INCLUDING where it is connected back to the top left of the tank! (I owe Tony a pint!) When one becomes even slightly "agism challenged", one tends to make assumptions, based on experiences from years, now, gone by. Not good. Also included are three (3) of the VENTED cap, an original cap, showing a little hole in the middle with a pin valve, plus holes all around the outside lip to VENT IT! No more excuses! Sorry Tony! Gordon Raymond

[Gordon Raymond]

George and all others watching my embarrassment, here's the last three photos of the VENTED OEM cap! Gordon Raymond

[alfabits]

Quote:

Originally Posted by Gordon Raymond Hi George, Hi Tony, Hi 101 /105 guy, Let me start by saying I must be suffering mind melt down. TONY IS 100% correct. 43 years working on these things and I should read more carefully, not trust opinions possibly gathered from other Alfa's, and not trusted the Alfa parts book. Here are a series of photo's of the #1365.85.063 "breather pipe" in it's entire glory, INCLUDING where it is connected back to the top left of the tank! (I owe Tony a pint!) When one becomes even slightly "agism challenged", one tends to make assumptions, based on experiences from years, now, gone by. Not good. Also included are three (3) of the VENTED cap, an original cap, showing a little hole in the middle with a pin valve, plus holes all around the outside lip to VENT IT! No more excuses! Sorry Tony! Gordon Raymond

[Gordon Raymond]

George,
You might try Christian Ondrak, OK parts in Germany for the correct OEM cap. The pin valve is a stubby nail like thing that hangs through the hole. Any liquid sloshed up closes the valve so it can't escape through the vents around the rim. I tested it by blowing on it. It seals about 90%. The OEM caps were painted black. Probably the only way to modify yours would be to disassemble it. They look like the outside is pressed over the inner riveted assembly. I'm not sure how it would come apart without damage. Try Christian first for an original. If that fails I may be able to scrounge up a restorable one.
Let me know. Best, Gordon Raymond

[Alfajay]

I just use the cheapie, universal, "bayonette"-style caps that they sell at NAPA auto stores. They don't seal all that tightly, so I suppose you could say that they self vent. I haven't noticed fuel sloshing out from the filler when the tank is full, though obviously that would be a safety hazard.

[101/105guy]

I would try drilling your cap to match Gordon's. It will vent and you will save the new chromed part.
Just keep under 1 G cornering and no gas will spill out! ;^)
Randy

[ecdysiast]

Seems to me that as long as there was no venting going on, simply drilling through the cap outside of the gasket would solve the problem. The people who made the replacement gas cap the original poster has forgot the holes.

Now, with gas fumes inside the cockpit when the tank is over half full I'll have to go out and check my own holes!

Jeffrey