Well, here's what a new gas tank looks like when it isn't vented. It collapses. I have a 1970 non-evap., non-vented system, with non-vented gas cap, which is correct for '70-71. I'm at a loss on why this happened, other than a bad design. I have posted on this before the tank was ruined, but it's a mystery for me. I am suspicious that they used vented caps until '69, and then again in '72 on. Did they run into this? Can any other 70 or 71 owners elaborate on their situation? Thanks
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Well, that sucks... Sorry, the devil made me do it *NM*
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Re: collapsing gas tank C3
Mark-----
Post a photo of the tank taken taken from the top.In Appreciation of John HinckleyComment
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Re: collapsing gas tank C3
I would find me a pooped out gas cap and fashion a valve stem to it and give it a shot of air. It will pop it out without much pressure. If it is a reproduction with OLAnderson logo on it, you can send it to me
TerryComment
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Re: collapsing gas tank C3
Mark,
In your text you mentioned non vented caps for '70 & '71's. Both of my '71's gas caps have the word SEALED stamped into it and a raised red colored metal tag with white lettering saying CAUTION OPEN SLOWLY. Are these considered vented or non vented.Comment
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Re: collapsing gas tank C3
Mark all 71 tanks were sealed type non vented. PaulComment
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Re: collapsing gas tank C3
Warren - the sealed caps are non-vented. That is what's on mine. I'm wondering if your tank has a vent valve on it to keep it from pressurizing, or as in my case, collapsing? Mine has a safety valve about the size of a quarter on the top and to the left of the filler neck. According to the supplier I bought it from, the manufacturer said it is only to release built up pressure, not keep it from becoming a negative atmosphere, as what happened in my case.Comment
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Re: collapsing gas tank C3
Joe - here is another pic from the top.
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Re: collapsing gas tank C3
Mark------
OK, from a combination of the 2 pictures that you posted I can tell you that this is the correct tank for the car. I could not be sure from just the first picture.
The valve that you noted which is to the left of the filler opening is a pressure/vacuum valve, notwithstanding what anyone else may have told you. It serves exactly the same function as a vented fuel cap, but allows a sealed fuel cap to be used. As a matter of fact, over 25 years ago, GM discontinued all 63-L69 fuel tanks which originally did not have this valve and replaced them with tanks WITH the valve. GM's instructions were that when an original tank was replaced with one of the SERVICE tanks with the valve, then a sealed cap was to be used. This, of course, would apply to all 1963-69 Corvettes.
My strong suspicion is that the pressure vacuum valve failed which caused unrelieved vacuum in the tank. That's the only thing that I can imagine would have caused a failure like this.
The pressure/vacuum valve cannot be replaced. Although it's conceivable that someone could unsolder and resolder a new valve (albeit a dangerous activity if not done properly), no valves like these are anywhere available as a seperate part. So, if one fails, the complete tank must be replaced.
An alternative would be to try to pressurize the tank to "pop out" the collapsed areas and then use a 63-69 vented style cap. To be honest, I would not even consider this alternative if it were me. Not for one second!In Appreciation of John HinckleyComment
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Re: collapsing gas tank C3
I'm thinking your old post said you have a 70 L-46, Non Calif.
I remember way back when I replaced the gasket on my fuel cap,(same car as yours), the only one available was a rubber one. The original was cork, and I noticed as soon as I changed it, there was a rather uncomfortable whosh when I opened the cap. Put the cork one back on. Guess it leaks enough to relieve the pressure.
I also had the fuel sucked through the carb, filling the oil pan. I fortunately opened the hood and smelled the gas before I started it. I blame this on that rubber cap seal, although many have suggested other causes.Comment
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Re: collapsing gas tank C3
Dennis-----
A CORK gasket on a Corvette fuel cap? I've never seen one. It's possible that it was unique to the 1970-only fuel cap, but it surprises me. 1963-1968 used a tan cellulose fibre gasket; 1969 and 71-74 used a rubber gasket. So, if 1970 used cork, it was the only one that did.In Appreciation of John HinckleyComment
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If it's new, I would return it
If this was a new tank you just bought, the manufacturer should make good on it and replace it for you. As Joe said, if the vent valve were functioning properly, it should be impossible to do this to the tank.
MarkComment
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Re: collapsing gas tank C3
Joe / All -
The supplier did send me a new tank, no charge. (it took about 45 minutes on the phone before the agreed to it). The manufacturer footed the bill, from what I was told. I too, thought that the valve was a two-way device, and not just to relieve pressure. I was told by the supplier that the manufacturer said it was only for releiving pressure. That might have been the supplier just feeding me a line...
I do have the new tank in, and have ordered a '69 vented-style cap, taking no chances!
Thanks for the responses.Comment
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Re: collapsing gas tank C3
Mark------
If the manufacturer told the supplier that the valve was only for pressure relief, then the supplier should have asked them "...then what provisions are there on the tank to relieve vacuum..."? The cap used with all these tanks with the valves is a sealed cap, so it can't be that (actually, the sealed cap WILL relieve pressure at a certain point if the pressure vacuum valve fails to do so but it won't relieve vaccum).
The fact is that if this is not a failure of the pressure/vacuum valve, then it must be that the tank was "weak" and could not withstand "normal" build up of vaccum. It's got to be one or the other. Either way, it's a problem with the tank.
On the other hand, if the manufacturer is correct and the valve is only designed to relieve pressure, then they're putting the wrong valves in the tank.In Appreciation of John HinckleyComment
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Re: collapsing gas tank C3
Not much pressure but quite a bit of air. Since the vender replaced the tank I don't expect there is any reason to try and pop it back into shape but, if was doing it I'd figure out a way to use water pressure rather than air.
Same pressure, smaller bang if something goes wrong.Comment
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