# 68 GTO Fuel Cap Issue?



## bgumpper (Feb 13, 2016)

Just picked up a 68 GTO and with a non functioning fuel gauge decided to fill it up. Well, under light acceleration, especially leaving the gas station, gas poured out of the neck and cap. The cap appears to be original and just wondering if that is just the way it is or if I should buy a new cap.


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## PontiacJim (Dec 29, 2012)

bgumpper said:


> Just picked up a 68 GTO and with a non functioning fuel gauge decided to fill it up. Well, under light acceleration, especially leaving the gas station, gas poured out of the neck and cap. The cap appears to be original and just wondering if that is just the way it is or if I should buy a new cap.



Ya, they do that if you have a vented cap, fill the tank chock full to top it off, and take off fast, but it should not pour out. As the car accelerates under a hard take-off, the nose typically lifts and the rear can squat, so this makes things worse when the tank is chock full. If you have weak or sagging springs in the rear, this is not helping either. Get the fuel level down a bit to get some weight off the rear as well as drop the gas level down and then test it to see what happens under a hard acceleration. 

You should also have a vent tube near the end of your fill tube. It should be a nipple on the side with a hose that goes up toward the trunk and then is connected to a U-shaped steel tube that hooks to the underbody bracket with the terminating end of the U-shaped tube pointing down. If this is missing, gas could also be pouring right out the nipple on the side of the filler neck when you accelerate.

There is also supposed to be one at the front of the tank as well - a rubber hose having a small filter on its end.

It may not hurt to replace the cap seeing its age BUT, you have to replace it with a like cap. If you get a non-vented cap, your engine will eventually create a vacuum within the tank as the fuel level goes down and you will starve the engine for fuel or possibly collapse your tank. So make sure you get a factory replacement from a reputable Pontiac parts supplier. Your local auto parts store will not have the correct one or they will have a Chinese knock-off that will look the same but isn't. :thumbsup:


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## bgumpper (Feb 13, 2016)

Thanks Jim, I'll take a look at all that stuff. Just thought it was odd how much gas poured out under acceleration, especially with a full tank.


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## pjw1967 (Mar 10, 2014)

This is what the tank vent looks like on my '67.

GTO Tank Vent by pjw1967 | Photobucket


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## GTO JUDGE (May 14, 2005)

Make sure you have the correct gas tank with the correct neck. A Friend with a '68 had the exact same issue you describe with gas pouring out, vent issue was first thought was not the issue and new gas caps didn't correct it. Turned out the angle of the neck was not correct. Gas tank was removed, vacuumed neck cut off a new one installed with the correct angle and the problem was resolved. Make sure the neck has the correct degree of angle.


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## geeteeohguy (Feb 2, 2008)

All of my '65-'67 GTO's with original tanks and vented caps would dump fuel on fast take offs with full tanks of fuel. Nature of the beast. Not a _lot _of fuel, but _some. _In close to 40 years of driving them, it never really concerned me.


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## bgumpper (Feb 13, 2016)

Well, I guess it's time to fess up. First, I bought the car from a friend who has bought and sold more muscle cars than I can count. He drove the car to my house with his dealer tag and with a non functioning gas gauge I decided to fill it up to make sure. Well he actually filled it up and having had and been around cars so long thought for sure he would know how to put a gas cap back on properly.

Shame on me for not checking that first and I think I'm good for now. I put some gas in yesterday for the first time and realized the cap wasn't even close to being put on properly.


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