Vented gas caps
Thread Starter
Pro
Joined: Apr 2005
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Vented gas caps
I continue to have concerns about the venting of my gas tank. I have a vette w/o the evaporative cannister (it never had one). So, the only venting to atmosphere the tank gets, is through the "vented" gas cap.
I went to fill it up the other day and the cap just about blew out of my hand. I have heard of some people drilling a small hole in the cap to ensure a good vent.
Anyone have experience with this? Until I come up with something, I'm going to run the cap without the rubber gasket.
Thanks.
I went to fill it up the other day and the cap just about blew out of my hand. I have heard of some people drilling a small hole in the cap to ensure a good vent.
Anyone have experience with this? Until I come up with something, I'm going to run the cap without the rubber gasket.
Thanks.
Former Vendor
Joined: Aug 2006
Posts: 76,656
Likes: 1,853
From: Jeffersonville Indiana 812-288-7103
St. Jude Donor '08-'09-'10-'11-'12-'13-'14-'15
Are you sure the cap vent is working? If you remove the gasket you’re going to leak gas out of the cap if you get any splash in the tank.
Racer
Joined: Nov 2006
Posts: 495
Likes: 1
From: Lubbock TX
what about putting on one of those locking gas caps where when you push the key in to turn, the extra pressure is released safely. But otherwise shouldnt your vented cap already of released the pressure built up?
Safety Car
Joined: Sep 2005
Posts: 4,229
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From: Orange County Ca
My 69 has a locking cap with a vent hole. Some times I get a little gas oozing out of the vent with a full tank on a hot day. Don't worry about a few drops. If it is hot enough to puke gas, it is hot enough to evaporate quickly.
I believe you do need a vent for the system to work properly. Be careful if you drill or hog out a hole, you only need a real small hole, or gas will splash out with a full tank or hard cornering. Try ultra small. You can always go bigger.
I believe you do need a vent for the system to work properly. Be careful if you drill or hog out a hole, you only need a real small hole, or gas will splash out with a full tank or hard cornering. Try ultra small. You can always go bigger.
Last edited by Sayfoo; Apr 12, 2008 at 10:41 PM.
Le Mans Master
Joined: Sep 2000
Posts: 9,078
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From: DFW TX
Cruise-In VII Veteran
St. Jude Donor '07
I have a gas hot water heater in my garage. I alway hate that night after a cruise and the garage wreaks of gas fumes.
To your point, I assume the gas is sloshing around before you stop at the gas station and causing some pressure. That and the return line from the fuel filter add additional pressure.
To your point, I assume the gas is sloshing around before you stop at the gas station and causing some pressure. That and the return line from the fuel filter add additional pressure.
Last edited by Budman68; Apr 12, 2008 at 11:28 PM.
Thread Starter
Pro
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The cap is working, as I can physically push in on the inside and you can see the movement of it; I think it might be too strong of a spring in the cap, because it shouldn't be a gigantic rush of air (enough to blow the cap off when you remove it) in my opinion. Originally, the 1970 non-California cars (mine) had a SEALED cap, which really doesn't make any sense at all; serious design oversight!
I will drill a tiny hole and that sounds like it should do the trick. I have tried a locking gas cap in the past, but it got stuck on the tank once, and that sucked, so I don't use it.
I wish there was a legitimate fix for this, as I can't believe there's only a handful of vettes with this problem. They went to a vented cap in '71 or '72 and more importantly, the EEC cannister which keeps the tank pressure in check. I'm wondering what a '64 or a '58 vette does for venting?
I will drill a tiny hole and that sounds like it should do the trick. I have tried a locking gas cap in the past, but it got stuck on the tank once, and that sucked, so I don't use it.
I wish there was a legitimate fix for this, as I can't believe there's only a handful of vettes with this problem. They went to a vented cap in '71 or '72 and more importantly, the EEC cannister which keeps the tank pressure in check. I'm wondering what a '64 or a '58 vette does for venting?
Pro
Joined: Jan 2006
Posts: 703
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From: Berwyn IL
ALL 1969-1972 (and maybe newer, but I don't know for sure) OEM Corvette gas tanks have a vent valve built into the gas tank, whether the car came with an evaporative canister or not. The gas cap was vented (stamped on the cap) until 1970 (when the cap has sealed stamped on it). The fuel tank has a vent valve regardless of the cap. The vent valve is soldered into the top of the tank.
If you have a 1969-1972 and there is a pressure built up in the tank it is a good chance the vent valve is malfunctioning -- unless the valve is mechanically blocked with something. This valve is not replaceable -- a new fuel tank is the fix. A temporary "solution" is a vented fuel cap, but at the chance of some spilled fuel when the tank is full.
If you have a 1969-1972 and there is a pressure built up in the tank it is a good chance the vent valve is malfunctioning -- unless the valve is mechanically blocked with something. This valve is not replaceable -- a new fuel tank is the fix. A temporary "solution" is a vented fuel cap, but at the chance of some spilled fuel when the tank is full.
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Drifting
Joined: Sep 1999
Posts: 1,970
Likes: 91
The cap is working, as I can physically push in on the inside and you can see the movement of it; I think it might be too strong of a spring in the cap, because it shouldn't be a gigantic rush of air (enough to blow the cap off when you remove it) in my opinion. Originally, the 1970 non-California cars (mine) had a SEALED cap, which really doesn't make any sense at all; serious design oversight!
I will drill a tiny hole and that sounds like it should do the trick. I have tried a locking gas cap in the past, but it got stuck on the tank once, and that sucked, so I don't use it.
I wish there was a legitimate fix for this, as I can't believe there's only a handful of vettes with this problem. They went to a vented cap in '71 or '72 and more importantly, the EEC cannister which keeps the tank pressure in check. I'm wondering what a '64 or a '58 vette does for venting?
I will drill a tiny hole and that sounds like it should do the trick. I have tried a locking gas cap in the past, but it got stuck on the tank once, and that sucked, so I don't use it.
I wish there was a legitimate fix for this, as I can't believe there's only a handful of vettes with this problem. They went to a vented cap in '71 or '72 and more importantly, the EEC cannister which keeps the tank pressure in check. I'm wondering what a '64 or a '58 vette does for venting?
As you say,your 70 should use a sealed cap. When you open it a "whosh "is normal. As someone has said the pressure relief valve on the tank will handle excess pressure. It's suppose to keeps the tank from collapsing. They seldom go bad, but I guess its possible.
I once had all the fuel in my tank get siphoned into the crankcase. I swore it had to do with the fuel cap. I had replaced the worn out cork gasket with a rubber one. Started to get that cap pop off you mention. Put a cork gasket,(which is what should be there). on the cap, and replaced the tank that developed a slight leak, and all is well.
Thread Starter
Pro
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I bought this tank new 2 yrs ago, from Quantra; it's an OEM correct tank. However, it is the 2nd new tank, as the first one I installed collapsed inward due to a vacuum lock. At the time, everyone I talked to said the built-in valve was only to relieve pressure, not to relieve vacuum. This tank has been okay, so far, with respect to vacuum, but I'm keeping my fingers crossed. I'm just getting really sick of having to worry and deal with a stupid tank. I will try a cork gasket, along with a tiny drilled hole in the cap. Thanks all!
Drifting
Joined: Sep 1999
Posts: 1,970
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[QUOTE=AirTrafficController;1564997997. However, it is the 2nd new tank, as the first one I installed collapsed inward due to a vacuum lock. At the time, everyone I talked to said the built-in valve was only to relieve pressure, not to relieve vacuum. tank. I will try a cork gasket, along with a tiny drilled hole in the cap. Thanks all![/QUOTE]
You are correct, the valve is to relieves to much pressure.
However the outward pressure that builds up pryor to the valve activating, is suppose to prevent the vacuum lock/ tank collapse.
Would seem a vented cap would solve both problems
You are correct, the valve is to relieves to much pressure.
However the outward pressure that builds up pryor to the valve activating, is suppose to prevent the vacuum lock/ tank collapse.
Would seem a vented cap would solve both problems
