is the gas cap supposed to vent? - Team Camaro Tech
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post #1 of 11 (permalink) Old May 12th, 01, 09:07 AM Thread Starter
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i have a 69 camaro 350. the car has been running bad sometimes and other times it runs good. i've been told its the timing, vacum modulator or the torque converter. i had a lot of pressure in my gas tank. when i took off the gas cap it sounded like i just unhooked a air line from a compressor. could a non-venting gas cap make my car run bad? when i release the pressure the car runs fine. thank you for any advice!
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post #2 of 11 (permalink) Old May 12th, 01, 09:37 AM
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as far as im know the gas cap is supposed to vent. also the might be a vent on top of your tank by the ring. the cap in my 68 is sealed but it still vents.
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post #3 of 11 (permalink) Old May 12th, 01, 05:27 PM
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My 69 has a vented cap.
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post #4 of 11 (permalink) Old May 12th, 01, 06:19 PM
David Pozzi
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They are supposed to be vented, but maintain five pounds pressure or so, to prevent fuel vapor from escaping.
There is a small spring loaded valve inside the cap if you have the proper one.

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post #5 of 11 (permalink) Old May 12th, 01, 06:59 PM
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I don't think mine vents cause when it is empty and I remove the cap it shoots tons of air out. Sometimes it also gets my hand wet frm a little gas residue

69 Camaro RS, 355ci mild cam, Preformer rpm intake, edelbrock 600 carb, 350 turbo w/ shift kit 2500 stall, 10 bolt 2.73 any more questions ask
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post #6 of 11 (permalink) Old May 13th, 01, 01:27 AM
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That's too much pressure. Get a new cap. My 69 makes the sightest hiss when I open it regardless of how much driving. I once had a car that I mistakenly plugged the vent. The tank started collapsing. You don't need that!
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post #7 of 11 (permalink) Old Mar 24th, 02, 09:52 PM
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I figured I'd resurrect an old post instead of starting a new one...

I'm noticed the same problem with my 69 and a lot of pressure in the tank. I took off the cap and gas sprayed everywhere...I probably could have shot the cap out into the driveway the pressure was so great. It says it's vented but it's probably worn out.

My motor is a pre-87 with TPI and an external electric pump. Is there anything else that could cause something like this? I've heard of gas boiling if the exhaust is too close, but I'm pretty sure I'm alright there.

I guess I'll buy a new cap this weekend...and try not to be paranoid. I swear every spring something always goes wrong.
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post #8 of 11 (permalink) Old Mar 25th, 02, 01:54 AM
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I would love to know why my "vented" gas cap does not vent. If I drive it around, the suction gets high enough to partialy collapse the tank. It has done this even with a new vented cap. I might have bought a defective cap but it was that way from the start and I drove it for years that way. Not sure what to do about it.

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post #9 of 11 (permalink) Old Mar 25th, 02, 10:15 AM
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I guess my car is a voodoo car...I have positive pressure in side the tank that'll blow the cap off when you turn the key.
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post #10 of 11 (permalink) Old Mar 25th, 02, 12:32 PM
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Torker just had his tank implode due to a faulty repro gas cap.

It bent the sending unit tube and float arm. A little air pressure fixed the tank but the sending unit needed to be removed for repairs.

We ended up brazing in a small galvanized tube (3/16" brake tubing) at the top of the filler neck so it faces rearward, and the end of the tube goes out behind the tank. The tube fits inside of the rubber sleeve. I'll likely to do the same thing to mine.

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post #11 of 11 (permalink) Old Mar 30th, 02, 12:21 PM
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A vented cap allows for air to replace fuel. For emission reasons, the cap is designed to only allow air into the tank, but not allow fumes out. Atmospheric pressure plays a role...for instance if the atmospheric pressue drops a couple of points, the fuel tank can really burp when you remove the cap. Nothing to be alarmed about though...IMO.
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