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Press in gas tank
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59 in Calif
Posted 2018-05-27 12:27 AM (#564059)
Subject: Press in gas tank


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Location: Hayward, Calif
Hey Guys, I took wife's 59 Dodge out for a spin yesterday. And stopped to put gas in it. When I removed the gas cap I got a small burst of air out from the tank. There was about 1/4 tank of gas in it, not setting in the sun, ( only been getting up to about 65 - 70 degrees weather lately ). I thought that was a bit odd. I looked at that new cap, it's not a vented cap. Don't know how I did that. So will get a vented cap and put on it. But it still puzzles me why there was press in that tank. I didn't smell any heavy gas fumes. Eng was running fine. Jerry
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mikes2nd
Posted 2018-05-27 7:01 AM (#564062 - in reply to #564059)
Subject: Re: Press in gas tank


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you probably still had winter blend in the car(creates more pressure)?


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Powerflite
Posted 2018-05-27 9:52 AM (#564072 - in reply to #564059)
Subject: Re: Press in gas tank



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Location: So. California
Pressure and vacuum are normal and happen every day. When it cools at night, the air and gasoline get cool and create a vacuum in the tank. If you open it at night, you will get an inrush of air. As the morning comes and it gets hotter, the tank will expand with pressure. A vented cap will expel that pressure and vacuum, but unfortunately, the new vented caps don't actually vent enough. It is as if they are set to vent only at very large pressures - too large for our huge tanks. I haven't done it yet, but I am considering to drill a tiny hole into the cap to see how that works.
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59 in Calif
Posted 2018-05-27 11:38 AM (#564076 - in reply to #564059)
Subject: Re: Press in gas tank


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Location: Hayward, Calif
I checked it this AM, probably about 55 -60 degrees in garage. I removed the cap and no in or out flow of air. And it probably had the winter blend of gas. I have about 3/4 tank of gas now. There is a small check valve in the underside of the cap. I put the cap up to my mouth and tried blowing thru it. It was pretty hard to build up enough press like that. I jammed a small piece of wire in it and unseated that valve. I could then blow and suck air thru it. So if I leave that wire jammed in there, I'm wondering just how good an idea this is. I can't say I noticed this happening in past gas fillups. Jerry
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1960fury
Posted 2018-05-27 2:37 PM (#564084 - in reply to #564072)
Subject: Re: Press in gas tank



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Powerflite - 2018-05-27 9:52 AM

Pressure and vacuum are normal and happen every day.


But not in an automobile gas tank.
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christine-lover
Posted 2018-05-29 9:02 AM (#564157 - in reply to #564084)
Subject: Re: Press in gas tank



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I noticed this when I fueled up my 61 yesterday, removed the cap and noticed pressure. Quite possibly the newer vented cap don't vent as they should. It does have a newer style vented cap.
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Darryl T
Posted 2018-05-29 2:26 PM (#564176 - in reply to #564157)
Subject: Re: Press in gas tank



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When I had this problem and mentioned it to my local NAPA "expert" he said the vented caps let air in as fuel is used, but not pressure out. Don't know if there is any truth to that.
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59 in Calif
Posted 2018-05-29 3:59 PM (#564186 - in reply to #564176)
Subject: Re: Press in gas tank


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Location: Hayward, Calif
This is the same thing I noticed when I checked out that cap. I could suck air thru it but really hard to blow air thru it. I'm not to fond of having that tank pressurized. I'm really seriously thinking of jamming a wire in that cap valve and let that tank breathe as it sees fit. I'd appreciate any other opinions on this. I can't say this ever happened on my 65 New Yorker, and it uses the same cap. Jerry
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ttotired
Posted 2018-05-29 4:50 PM (#564193 - in reply to #564059)
Subject: Re: Press in gas tank



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I don't have a "59" anything, so I might be wrong, but my 60 Plymouth has a thin steel line that goes from the filler neck around the side and to the front of the tank (in the diff tunnel) where it then connects to a small rubber hose and then to a small hook shaped pipe, this is the vent pipe

I wonder if yours is the same and maybe it got blocked up with mud or a wasp or something?

Vented caps do only let air in, if you do the wire thing, you risk fuel coming out of the filler neck while driving, that's why the vent one way

Just remember, your needle and seat take about 5 psi to open, if your not getting flooding issues, you may not have a problem, but I would look for the vent tube

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Powerflite
Posted 2018-05-29 4:57 PM (#564195 - in reply to #564059)
Subject: Re: Press in gas tank



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Location: So. California
None of my '57's or '58's have a vent tube. I think that's where the problem lies.
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60 dart
Posted 2018-05-29 11:27 PM (#564222 - in reply to #564059)
Subject: Re: Press in gas tank



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Location: WHEELING,WV.>>>HOME OF WWVA
vent tube = non vented cap . no vent tube =vented cap -----------------------------------------------------later
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