Gas tank pressue
Thread Starter
Pro
Joined: Mar 2010
Posts: 615
Likes: 25
From: Graham NC
Gas tank pressue
Hello, the last couple times after driving the car and taking off the gas cap, I noticed a high pressure hissing swooshing sound. Is this normal and any thoughts and remedies are appreciated. Thank you
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From: Sunshine Coast, Queensland, Australia
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I'm thinking a vented gas cap will get you out of the woods.
The environmentally correct repair could be a bit more involved.
The environmentally correct repair could be a bit more involved.
Safety Car
Joined: May 2001
Posts: 4,757
Likes: 1,647
From: Fairfax Virginia
By 1971 there were probably some venting equipment on your fuel system.
By going to a vented gas cap you will be potentially bypassing the issue itself. Take your Factory Service Manual and troubleshoot the problem with the venting. I have a 1968 BB C3 and it's gas cap is a vented type which works great. My car has no fuel tank vent system and has never has any problems with fuel delivery.
It is up to you personally whether or not you fix the issue or just switch to the vented gas cap. The difference might be gas fumes when parked in a garage.
After looking at ZIP PRODUCTS I was surprised to see the vented gas cap listed for the 1971 models. It seems that your fuel system is a bit more complicated than my 1968's.
When it comes to anything related to gasoline I tend to try and fix it properly. Pressurized gasoline is even more dangerous!
By going to a vented gas cap you will be potentially bypassing the issue itself. Take your Factory Service Manual and troubleshoot the problem with the venting. I have a 1968 BB C3 and it's gas cap is a vented type which works great. My car has no fuel tank vent system and has never has any problems with fuel delivery.
It is up to you personally whether or not you fix the issue or just switch to the vented gas cap. The difference might be gas fumes when parked in a garage.
After looking at ZIP PRODUCTS I was surprised to see the vented gas cap listed for the 1971 models. It seems that your fuel system is a bit more complicated than my 1968's.
When it comes to anything related to gasoline I tend to try and fix it properly. Pressurized gasoline is even more dangerous!
Melting Slicks
Joined: Aug 2001
Posts: 3,050
Likes: 124
From: Wichita KS
Take ctmccloskey's advice and sort your pressure issue out.
In process of replacing fuel tank on my 71. Driver's side has this Rube Goldberg system of dealing with gas fumes BEFORE fumes are sent forward to charcoal canister and ultimately engine. If fuel tank was dropped for repair/replacement, then don't be surprised if someone capped off this apparatus at the tank.
As ctm stated, pressurized gasoline is not a good thing.
Your 1971 Assembly Manual should help. May need one of those camera on a stick (flex cable) to see over there. I would open fuel door and push rubber dam aside, to fish camera cable to left side of fuel tank. Trying to reach from below, muffler is in your way.
Mapman
Le Mans Master
Joined: Aug 2017
Posts: 8,336
Likes: 2,810
From: Cool Northern Michigan
The tank is not pressurized where fumes blow out necessarily. That was somewhat common back in the day when you just filled the tank and because of expansion on a hot-hot day.
Raw fuel would actually drip on the ground. (Very few of my cars did that, too poor to fill the tank)
But with the O.Ps case, it's under pressure, but it's a vacuum. The tank is starving for air. I believe the vent system or lack of, is the issue.
In which case, a tank under vacuum is not dangerous when opened.
Back then, the owner's manuals mentioned to open cap slowly. Swoosh, air goes in.
I have heard of extreme cases where the tank actually tried to collapse with an indentation, when tanks were thinner steel.
That, is one strong fuel pump, with no return line or venting.
Raw fuel would actually drip on the ground. (Very few of my cars did that, too poor to fill the tank)
But with the O.Ps case, it's under pressure, but it's a vacuum. The tank is starving for air. I believe the vent system or lack of, is the issue.
In which case, a tank under vacuum is not dangerous when opened.
Back then, the owner's manuals mentioned to open cap slowly. Swoosh, air goes in.
I have heard of extreme cases where the tank actually tried to collapse with an indentation, when tanks were thinner steel.
That, is one strong fuel pump, with no return line or venting.
Thread Starter
Pro
Joined: Mar 2010
Posts: 615
Likes: 25
From: Graham NC
thank you, the car had vented gas cap when I got it 15 yeas ago. I just purchased a new gas cap from zip and maybe that will help.
By 1971 there were probably some venting equipment on your fuel system.
By going to a vented gas cap you will be potentially bypassing the issue itself. Take your Factory Service Manual and troubleshoot the problem with the venting. I have a 1968 BB C3 and its gas cap is a vented type which works great. My car has no fuel tank vent system and has never has any problems with fuel delivery.
t
It is up to you personally whether or not you fix the issue or just switch to the vented gas cap. The difference might be gas fumes when parked in a garage.
After looking at ZIP PRODUCTS I was surprised to see the vented gas cap listed for the 1971 models. It seems that your fuel system is a bit more complicated than my 1968's.
When it comes to anything related to gasoline I tend to try and fix it properly. Pressurized gasoline is even more dangerous!
By going to a vented gas cap you will be potentially bypassing the issue itself. Take your Factory Service Manual and troubleshoot the problem with the venting. I have a 1968 BB C3 and its gas cap is a vented type which works great. My car has no fuel tank vent system and has never has any problems with fuel delivery.
t
It is up to you personally whether or not you fix the issue or just switch to the vented gas cap. The difference might be gas fumes when parked in a garage.
After looking at ZIP PRODUCTS I was surprised to see the vented gas cap listed for the 1971 models. It seems that your fuel system is a bit more complicated than my 1968's.
When it comes to anything related to gasoline I tend to try and fix it properly. Pressurized gasoline is even more dangerous!
Thread Starter
Pro
Joined: Mar 2010
Posts: 615
Likes: 25
From: Graham NC
Thank you. I had the car for 15 years and the pressurized tank is a new problem,. I am still exploring and did purchase vented cap, maybe the old one is not working properly.
jbakyy
Take ctmccloskey's advice and sort your pressure issue out.
In process of replacing fuel tank on my 71. Driver's side has this Rube Goldberg system of dealing with gas fumes BEFORE fumes are sent forward to charcoal canister and ultimately engine. If fuel tank was dropped for repair/replacement, then don't be surprised if someone capped off this apparatus at the tank.
As ctm stated, pressurized gasoline is not a good thing.
Your 1971 Assembly Manual should help. May need one of those camera on a stick (flex cable) to see over there. I would open fuel door and push rubber dam aside, to fish camera cable to left side of fuel tank. Trying to reach from below, muffler is in your way.
Mapman
Take ctmccloskey's advice and sort your pressure issue out.
In process of replacing fuel tank on my 71. Driver's side has this Rube Goldberg system of dealing with gas fumes BEFORE fumes are sent forward to charcoal canister and ultimately engine. If fuel tank was dropped for repair/replacement, then don't be surprised if someone capped off this apparatus at the tank.
As ctm stated, pressurized gasoline is not a good thing.
Your 1971 Assembly Manual should help. May need one of those camera on a stick (flex cable) to see over there. I would open fuel door and push rubber dam aside, to fish camera cable to left side of fuel tank. Trying to reach from below, muffler is in your way.
Mapman
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