fuel leak gas cap 71 LS-5
I have a sealed cap now. It appears like my gas cap is leaking fuel. I had changed the cap gasket as I smelt gas when tank was full. It seemed to improve but still having problem so I change the gasket on fuller neck which, when I took the neck off, the filler neck gasket was mostly gone. I filled the tank above the bottom of neck to test. In a short time it started leaking from cap and when I open cap the fuel was right up to the cap. I was on an incline facing down,so I moved the car to flat level and the fuel level lowered. I assume that even with the fuel up to the cap it should not come out of a sealed cap. Is that correct? The cap seems tight so I am wondering if maybe I need to change filler neck too? My cap now is a silver color but online some of them are cadmium plated. I also see on corvette central their cap is listed as good through early 71. My car was produced on 3/22/71 so I do not think early. So my question is what should be my next step? Second question: What is the proper cap and where best to get it? Thanks, Ed
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Re: fuel leak gas cap 71 LS-5
Does your fuel cap have a rubber gasket or a cardboard gasket? I've found that the rubber gaskets swell over time and don't seal well. I've installed a cardboard gasket and that seemed to fix the problem. -
Re: fuel leak gas cap 71 LS-5
Thanks. The cap gasket has not been in long. It is fiber type, not rubber. I am not sure if there is a way to know if cap is faulty other than changing it. There seems to be a good fit but no vacuum to hear.Comment
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Re: fuel leak gas cap 71 LS-5
Ed------
I'm not aware of any 1970-74 fuel cap that used a fiber gasket. In any event, a new cap is available from GM. It's GM #3994339. It won't be configurationally correct for a 1971 but it will SERVICE your application. You could, at least, obtain one to see if it corrects your problem.
Your problem could also be due to a leaking pressure/vacuum valve on the tank. This valve is located several inches to the left of the filler opening. If this valve leaks, the fix is a new tank. While a radiator shop (many of which also repair fuel tanks) might be able to solder in a new valve, I don't know of any source for these valves.In Appreciation of John HinckleyComment
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Re: fuel leak gas cap 71 LS-5
Ed
The correct cap for your car has a silver plated finish and a red label with the wording "OPEN SLOWLY CAUTION"1971 Gas Cap 1st Design.jpg The rubber gasket should be the best at sealing the tank filler neck the paper gasket would eventual absorb gas and leak. I am not saying that the rubber would not swell if it is old type rubber not designed for alcohol.
My question would be why are you filling the tank to the bottom of the filler neck? With the expansion and contraction of the fuel due to temperature changes this could cause problems. When I owner and drove my 1971 I would never fill the tank to that level even in storage. I would leave at least 1" when driving the car after fueling and 2 " for storage space from the top of the tank to the level of the fuel. At the level you are filling the tank you are also having fuel sitting on the check ball in the fuel/vapor check valve (EVAP for the Charcoal Canister) on the left side of the tank. Which then could be prone for leakage.
So my suggestion would be leave at least 2" for storage filling to the level you are is not a good thing.Comment
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Re: fuel leak gas cap 71 LS-5
Thanks Joe and Paul. I do not have same cap as in Paul's picture. Mine has caution stamped in top and looks a little different. Where can I get correct cap? Are they available new? It is a good point not to fill to full for all the reasons you listed. I did so as a test of leaks after putting in a new filler neck gasket. Maybe not such a good idea as Paul indicates. I still would like to know how to test seal on my gas cap though. Thanks, EdComment
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Re: fuel leak gas cap 71 LS-5
Ed Paragon sells a cap that is as good as it gets for now there are errors in it the red label is of an incorrect size and the handle is spot weld in backwards. The other option is to find a used cap have it replated or just replace the gasket with a new one or buy one from a people who restore the caps some should be listed in the Driveline. They are not cheap.
Here is a link to Paragon. https://www.paragoncorvette.com/p-35...iller-cap.aspx
As far as testing you could do what you are doing or make tooling that could simulate the neck and cap installed and apply a liquid under a slight pressure to see where the leak is occurring. Not easy to do. I do not remember ever seeing a gas cap tester for cars of this era as is the case for today's caps.
A2378.jpgHere is a photo of the cap you may have it is a service replacement for a 1971 was used on 1972 and later Corvettes.Comment
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Re: fuel leak gas cap 71 LS-5
My 70 original gas cap is still in use. I know it still seals the closed system because of the pressure release I hear when I remove the gas cap for a fill up. I have 160K + miles on my 70 and when I was making a road trip I would fill the tank to the brim and get back on the road. Never had a problem with this procedure. My 70 was not equipped with a charcoal canister system from the factory.Comment
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Re: fuel leak gas cap 71 LS-5
I seem to remember the filler neck gasket as a cork material, not paper. Is it my memory or they are now servicing the gasket with a different material?TerryComment
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Re: fuel leak gas cap 71 LS-5
Terry
The initial gasket conversation was about the gasket on the gas cap. Ed added that he had also replaced the filler neck gasket and I agree with you the originals were a cork type material much like a valve cover gasket. Do not know what type of material they using to make the gaskets of today for the filler neck.Comment
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In Appreciation of John HinckleyComment
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Re: fuel leak gas cap 71 LS-5
Thanks Joe and Paul.This is my cap now: DSCN8339.jpgDSCN8337.jpgI am not going for judging but do try to replace with proper parts. From what you say even the Paragon one is not 100% accurate. Would it past judging? Mine seems to be of the replacement type but silver color. I am not sure if getting a new cap will solve my problems but I guess I have to buy a new cap to find out? I probably will not fill tank all the way any more but still think I should have a proper working cap. One cap is about $30 and the other $60. Any other thoughts to add? I see there are some other posts for me to check too. Thanks, EdComment
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Re: fuel leak gas cap 71 LS-5
I used a cork gasket. Pretty thin with 9 bolt holes. Also I noticed that each of the bolts have a rubber washer too.Comment
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Re: fuel leak gas cap 71 LS-5
Ed
The rubber washer on the bolt is to seal the bolt due to it entering the tank thru the nut plate.Comment
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