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Old 03-31-2021, 01:02 PM
Terry M. Hunt Terry M. Hunt is offline
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Default Vented gas cap

My 64 GTO has a fuel tank vent on the filler neck. I’m using a “Vented. Anti Surge” repro gas cap from our host. If I tighten this cap all the way to the right, I often get a big whoosh of air when removing it for a fill up signaling built up pressure in the tank. Only way to avoid this is to only tighten the cap to the first stop and not all the way to the second stop. If the tank and the cap are both vented, how the h can this happen? If the tank is vented at the filler neck, should the cap then be a non vented cap? Yes, I have tested the vent on the filler neck and it is not blocked: obstructed.

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  #2  
Old 03-31-2021, 01:18 PM
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bill ryder bill ryder is offline
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Cap and tank don't match up. Cap must be sealing below vent tube.

"Bill"!

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Old 03-31-2021, 01:23 PM
Terry M. Hunt Terry M. Hunt is offline
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Default Vented gas cap

Okay, I’m an idiot. The fuel tank is NOT vented on the filler neck. I was going by memory and having too many cars makes it easy to make a goof like this. Soooo, the question is really why am I getting pressure build up in the tank if I’m using a vented cap? How would I test this cap(it’s newish, butwe all know that often means nothing) to be sure it is actually allowing the tank to vent?

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Old 03-31-2021, 01:39 PM
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Wrong cap is a guess. Is tank new or original?

"Bill"!

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Old 03-31-2021, 02:36 PM
Terry M. Hunt Terry M. Hunt is offline
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Default Vented gas cap

Original tank/repro cap. The bottom(tank side) of cap has a small hole in the center through which I can see what appears to be a black rubber diaphragm. When I blow really hard into this hole I can feel the diaphragm flex away from the pressure I’m creating and the air starts to flow. The problem seems to be the amount of pressure it is taking to get this diaphragm to move and allow tank pressure to be vented. I would have thought it would activate at a much lower pressure, so I’m not surprised that I get the big whoosh I get indicating the tank is not venting.. It’s simple enough to just not crank the cap down tight, but it really bugs me when stuff does not operate as it should and I have to band aid or rig it some way so it will.

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Old 04-01-2021, 05:07 AM
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JSchmitz JSchmitz is offline
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You need to get a different vented gas cap.

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