Vented or Non-vented Fuel cap ? - Chevelle Tech
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post #1 of 10 (permalink) Old Jun 21st, 20, 1:50 PM Thread Starter
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Sam
 
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Vented or Non-vented Fuel cap ?

64' Malibu, 350, 4-speed. I filled up today and just happened to read my fuel cap, non-vented. I have been having some fuel gauge up and down readings at the dash. Topped off needle gone, ran a bit to to needle at 12:00 added 7 gallons as a test. needle moved a little. Just curious if there is a plus/minus for vented cap or if it matters.

Thanks,

Sam in Lansing, Michigan
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post #2 of 10 (permalink) Old Jun 21st, 20, 8:44 PM
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Jeff
 
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If your tank is stock it should already have a vent tube between the tank and axle that goes to the passenger side, up through the trunk, then back down and venting into the rear passenger wheel well. If it's working correctly non-vented cap is what you should use.

*Jeff*

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post #3 of 10 (permalink) Old Jun 21st, 20, 10:07 PM
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Verle
 
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re: Vented or Non-vented Fuel cap ?

Quote:
Originally Posted by Hotwire View Post
If your tank is stock it should already have a vent tube between the tank and axle that goes to the passenger side, up through the trunk, then back down and venting into the rear passenger wheel well. If it's working correctly non-vented cap is what you should use.
This is correct. If you have a vented cap you will likely spill gas under acceleration. The fuller the tank the more spill.
Open the trunk and look toward the back right corner, you should see a tube that makes a loop. That is the vent mentioned.
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post #4 of 10 (permalink) Old Jun 21st, 20, 10:40 PM
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re: Vented or Non-vented Fuel cap ?

And vented cap or non vented cap isn't going to affect your gas gauge since your tank has the atmosphere venting tube as described above which vents the tank 100% of the time, running or not.


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post #5 of 10 (permalink) Old Jun 22nd, 20, 4:40 AM
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re: Vented or Non-vented Fuel cap ?

vented caps let air in to keep from pulling a vacuum in the tank. unless somebody alters with a drill or it's just shot they don't let fuel out.

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post #6 of 10 (permalink) Old Jun 22nd, 20, 11:57 AM
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Greg.
 
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re: Vented or Non-vented Fuel cap ?

My 67 Gas Tank Vent Tube is on the Passengerside in the Trunk


67 Chevelle Malibu SS Cdn
Born 283 / PG / A51
468/TH400 2,500 stall/ S60 3.70 Gs
Prev Best on M/T ET S/S #3454 street Tires/Dress 2018/05/20
60' = 1.664
1/8 = 7.532 et / 91 mph
1/4 = 11.814 et / 115 mph
NEW Best with 3,500+ Stall TC 2019/09/08
60' = 1.547
1/8 = 7.311 et / 91.76 mph
1/4 = 11.595 et / 114.28 mph


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post #7 of 10 (permalink) Old Jun 23rd, 20, 7:17 AM
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re: Vented or Non-vented Fuel cap ?

Quote:
Originally Posted by Tom Mobley View Post
vented caps let air in to keep from pulling a vacuum in the tank. unless somebody alters with a drill or it's just shot they don't let fuel out.
Not all vented caps have the "one way" vent.
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post #8 of 10 (permalink) Old Jul 13th, 20, 8:19 PM Thread Starter
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Sam
 
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re: Vented or Non-vented Fuel cap ?

I really appreciate all the replies, I do have the vent in the trunk, and I actually just replaced the fuel tank and sending unit. The tank is still settling in, I can tell because the filler tube clearance on the bottom is opening up more. I carry a 9/16 ratchet wrench to tweek the nuts and bolts, I'll trim the bolts when I feel it's settled all the way.
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post #9 of 10 (permalink) Old Jul 13th, 20, 8:20 PM Thread Starter
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re: Vented or Non-vented Fuel cap ?

Thank you, very good information.
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post #10 of 10 (permalink) Old Jul 13th, 20, 9:32 PM
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Re: Vented or Non-vented Fuel cap ?

Those vents are favorite locations for dirt dobbers to nest and clog things up. At one time I had five 67 Chevelles, three of which were parts cars. Four of the vent tubes were clogged. Music wire and carb cleaner were what I used to clean them out.

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