vented or non-vented gas tank? - Chevelle Tech
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post #1 of 4 (permalink) Old Sep 19th, 11, 5:01 PM Thread Starter
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Dave
 
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Location: Chesterland, OH
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vented or non-vented gas tank?

This might sound dumb, but what's the difference between having a vented vs. a non-vented gas tank? Or maybe a better way to ask, why would you want one style versus the other?

I have a '70, currently with a small block. Nothing is original on my car, and I do not have the charcoal canister or any of that. I do not care about originality, only functionality. I just want something that works and doesn't spill gas out the neck on acceleration. OPG lists a non-vented tank for my car.

I just want to make sure I get the right tank and gas cap.

-Dave

'70 Chevelle ZZ383/700r4/3.55, 12.25@108 -- Megasquirt2-Extra, Holley Stealthram / Hotchkis A-arms / Hotchkis Springs / B-body 12" brakes / 1.25" F-body swaybar
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post #2 of 4 (permalink) Old Sep 19th, 11, 5:24 PM
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Claude
 
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Re: vented or non-vented gas tank?

Quote:
Originally Posted by ChevelleFan70 View Post
This might sound dumb, but what's the difference between having a vented vs. a non-vented gas tank? Or maybe a better way to ask, why would you want one style versus the other?

I have a '70, currently with a small block. Nothing is original on my car, and I do not have the charcoal canister or any of that. I do not care about originality, only functionality. I just want something that works and doesn't spill gas out the neck on acceleration. OPG lists a non-vented tank for my car.

I just want to make sure I get the right tank and gas cap.

-Dave
A vented tank is correct for a '70. I think (but not 100% sure) that non-vented systems began a few years later, maybe sometime around '74 or later...(?)

Claude.

1971 Chevelle "SS 496"
1987 Buick Grand National 9.48 @ 142 mph
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post #3 of 4 (permalink) Old Sep 19th, 11, 7:21 PM
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Bruce
 
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Re: vented or non-vented gas tank?

If you do a search of this site you'll find quite a bit of discussion on the subject of vented vs. Not-vented. Not-vented gas caps were used through the 1969 model year. The tank itself has a vent at the front of the tank, but the cap is imprinted "NOT VENTED." Beginning with the 1970 model year the "VENTED" gas caps were used. The '70 Chevelle's fuel system included pollution control systems on the engine. Some owners have removed (gasp!) the controls and then found the "VENTED" gas caps no longer functioned properly. What's bizarre is that the "NOT-VENTED" caps go on a vented tank, and the "VENTED" caps go on what is basically a closed system! Confused? Me too.

So your question depends on your engine -- do you have the factory controls? If so then you would use the "VENTED" gas cap. If you do not, then you could A) modify your "VENTED" gas cap by drilling two holes in it to allow air to enter the tank, or B) replace the tank and the cap with the aftermarket tank/cap, or C) If you're not having a problem don't "fix it." Since your engine does not have the polution controls you'd pick "A" if you're having problems and "C" if you're not. BTW: The Not-vented Gas Cap does not fit the factory Vented Tank, and the Vented Cap does not fit the factory Not-vented cap.

BOTTOM LINE: If you're not having a problem don't "fix it."

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post #4 of 4 (permalink) Old Sep 20th, 11, 8:12 AM Thread Starter
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Dave
 
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Re: vented or non-vented gas tank?

Quote:
Originally Posted by NickeyChevelle View Post
If you do a search of this site you'll find quite a bit of discussion on the subject of vented vs. Not-vented. Not-vented gas caps were used through the 1969 model year. The tank itself has a vent at the front of the tank, but the cap is imprinted "NOT VENTED." Beginning with the 1970 model year the "VENTED" gas caps were used. The '70 Chevelle's fuel system included pollution control systems on the engine. Some owners have removed (gasp!) the controls and then found the "VENTED" gas caps no longer functioned properly. What's bizarre is that the "NOT-VENTED" caps go on a vented tank, and the "VENTED" caps go on what is basically a closed system! Confused? Me too.

So your question depends on your engine -- do you have the factory controls? If so then you would use the "VENTED" gas cap. If you do not, then you could A) modify your "VENTED" gas cap by drilling two holes in it to allow air to enter the tank, or B) replace the tank and the cap with the aftermarket tank/cap, or C) If you're not having a problem don't "fix it." Since your engine does not have the polution controls you'd pick "A" if you're having problems and "C" if you're not. BTW: The Not-vented Gas Cap does not fit the factory Vented Tank, and the Vented Cap does not fit the factory Not-vented cap.

BOTTOM LINE: If you're not having a problem don't "fix it."
No factory controls. Bottom line is that I *am* having a problem. Despite getting it flushed, I seemed to be constantly getting a lot of dirty gunk into the pre-filter for my EFI pump (car was EFI past couple years, currently has a carb, but EFI will return).

So I bought a new tank, and I kinda ordered before I knew exactly what I needed.. (I know, I know..) I ordered a non-vented tank for a '70 Chevelle from OPG.. but it didn't come with a gas cap, so I'm just trying to make sure I buy compatible parts at this point.

-Dave

'70 Chevelle ZZ383/700r4/3.55, 12.25@108 -- Megasquirt2-Extra, Holley Stealthram / Hotchkis A-arms / Hotchkis Springs / B-body 12" brakes / 1.25" F-body swaybar
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