Vented Gas Cap Not Venting - Team Camaro Tech
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post #1 of 8 (permalink) Old Sep 23rd, 09, 06:32 AM Thread Starter
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Vented Gas Cap Not Venting

I bought a new GM vented gas cap for my '69 Camaro last year. I drove the car and after parking it I heard a high pitched hissing sound. I followed the sound to the gas cap. I pulled the gas cap off and heard a big whoosh of air rushing into the tank. Apparently the new "vented" gas cap is not venting. Does anyone know how to remedy this issue?

Northstar
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post #2 of 8 (permalink) Old Sep 23rd, 09, 06:43 AM
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Re: Vented Gas Cap Not Venting

Normal effect. Cap allows air in, not out. Pressure on tank keeps fuel pump primed.
Cap keeps fumes inside tank, not in enclosed garage.

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post #3 of 8 (permalink) Old Sep 23rd, 09, 07:06 AM Thread Starter
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Re: Vented Gas Cap Not Venting

The problem is the cap is not letting air in. The only pressure developed on the fuel pump is a vacuum in the tank. The vacuum being caused by the fuel pump removing fuel from the tank. This doesn't seem normal to me. Am I wrong?

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post #4 of 8 (permalink) Old Sep 23rd, 09, 07:16 AM
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Re: Vented Gas Cap Not Venting

Quote:
Originally Posted by Everett#2390 View Post
Normal effect. Cap allows air in, not out. Pressure on tank keeps fuel pump primed.
Cap keeps fumes inside tank, not in enclosed garage.
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post #5 of 8 (permalink) Old Sep 23rd, 09, 09:45 AM
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Re: Vented Gas Cap Not Venting

I think people are missing his point. He is saying that the cap is not working in the way that you guys are describing.

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post #6 of 8 (permalink) Old Sep 23rd, 09, 02:53 PM
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Re: Vented Gas Cap Not Venting

Thanks for pointing the situation out. Yes, a simple check is to suck on the inside of the cap, cap should allow air to pass into the tank.

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post #7 of 8 (permalink) Old Sep 23rd, 09, 05:17 PM
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Re: Vented Gas Cap Not Venting

mmmm nothing like the taste of 89 octane!

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post #8 of 8 (permalink) Old Sep 24th, 09, 01:48 AM
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Re: Vented Gas Cap Not Venting

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Originally Posted by lortsie View Post
mmmm nothing like the taste of 89 octane!

Try seven year old 93 octane. That's what my last mouthful was. Exquisite on the palette with an intriguing bouquet. No ethanol so it didn't even count as one of my vegetables for the day. But it did actually fire up in the car.

Northstar, I bought a vented cap from AutoZone recently and it seems to work fine. It was a Stant I believe. My tank definitely pressurizes. The cap has a warning "Open Slowly" and believe me you have to. It blows little gas sprinkles out if you crack it too fast.

The vented caps do only let air in but if the tank pressure gets high enough they act like a radiator cap and will let air out. It's quite possible that's what you heard as the exhaust heat will cause the fuel/vapors to expand. Next time you drive it for awhile, hold a well worn dollar bill by the edge of the cap while you open it and see if it gets blown back or sucked toward the edge.

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