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Discussion Starter · #1 ·
Has anyone encountered a problem with their fuel cap leaking when making a sharp right turn after filling the gas tank? My '98 Formula started this not too long ago, maybe a month or so. I replaced the original gas cap last year with an AC/Delco but now I'm thinking I should've tried for an OE one. It did not do this before the replacement and I had the same issue with a '94 Formula I previously owned. If it weren't for the fact that the gas runs down the side of the 1/4, I wouldn't care. Makes me wonder why the designers didn't leave the filler neck under the trunk lock!
 

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Ramblin' Wreck
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My 98 does that because the metal flapper inside the neck is bent and doesn't block the surges anymore. No way to fix it without replacing the tank, so I just never fill above 3/4. I have the genuine GM replacement cap and the original cap but neither one stops the leaking.

And according to the GM parts manuals, the 98 cap is unique and can't use any other year. Probably a bad design.
 

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Discussion Starter · #3 ·
Update: In the four and a half years since I posted this, I have gone through 5 fuel caps. Typically a new fuel cap stops the problem for a few months but doesn't solve the problem. The other day I thought about perhaps replacing just the o-ring on the gas cap with a thicker one. When I looked at the o-ring, I noticed that there is a small gap between the o-ring itself and the lip that prevents the o-ring from moving. That gap, I believe, is the reason why fuel will leak out of the filler neck while making a right turn on a full tank. I ultimately decided to add another o-ring that was thinner to fill the gap, so I went to my local hardware store. I purchased an o-ring that is the same diameter as the existing o-ring but was thin enough to fill the gap. After installing the additional o-ring on the cap and the cap on the car, I drove in tight circles in the parking lot. When I looked at the side on the car, no new fuel had come out of the filler neck. Hopefully this will continue to solve the problem and I will no longer need to replace the fuel cap.
 

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Ramblin' Wreck
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You are band-aiding the problem. It may work for a while. Have you inspected the flapper valve in the neck yet?

I did something similar since it is very difficult to fix the valve. I wrapped and tied a 1/4" nylon cord around the cap under the seal to give it some extra height. Just another band-aid fix that does not work perfectly.
 
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