VACUUM SOUND WHEN REMOVING GAS CAP?????????
Thread Starter
Safety Car
Joined: Mar 2002
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From: Okeechobee Florida
VACUUM SOUND WHEN REMOVING GAS CAP?????????
when removing the gas cap to fill up i get this huge vacuum from the cap as i remove it...
whats up with that?? is this normal?
thanx.....
whats up with that?? is this normal?
thanx.....
Thread Starter
Safety Car
Joined: Mar 2002
Posts: 4,411
Likes: 1
From: Okeechobee Florida
Re: VACUUM SOUND WHEN REMOVING GAS CAP????????? (One GM A Tech)
really? i didnt think that this could be normal...is my cap messed up or is a design thing? did they actualy put a non vented cap on the car when they built it?
it seems as tho if there is a vacuum in the tank that the engine would have a hard time "pulling" the gas to the engine...
it seems as tho if there is a vacuum in the tank that the engine would have a hard time "pulling" the gas to the engine...
Burning Brakes
Joined: Mar 2002
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From: If you can read this, thank a teacher. If it is in English, thank a veteran.
Cruise-In IV Veteran
Cruise-In V Veteran
Re: VACUUM SOUND WHEN REMOVING GAS CAP????????? (SIGNGUY)
In the warm summer months, my Shark sings to me. When the air passes through the vented gas cap, something is acting as a reed and the cap sings. It sounds like a dolphin or whale or something. She does it both while driving and at rest and has done it since I bought her. I have actually caught myself talking back to the car when she makes these noises. Might as well, I talk to my cat and dogs too. :crazy:
Thread Starter
Safety Car
Joined: Mar 2002
Posts: 4,411
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From: Okeechobee Florida
Re: VACUUM SOUND WHEN REMOVING GAS CAP????????? (L48Shark)
WOW...im enlightened...now that i think about it, sometimes when taking off from a dead stop it kinda "hogs up" like its starving for fuel but otherwise runs perfectly...
could this be why????
could this be why????
Team Owner
Joined: Jul 1999
Posts: 26,545
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From: Huntersville NC
Re: VACUUM SOUND WHEN REMOVING GAS CAP????????? (SIGNGUY)
WOW...im enlightened...now that i think about it, sometimes when taking off from a dead stop it kinda "hogs up" like its starving for fuel but otherwise runs perfectly...
could this be why????
could this be why????
Safety Car
Joined: Sep 1999
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From: AnyTown NJ
St. Jude Donor '08-'09-'10-'11-'12-'13-'14-'15
Re: VACUUM SOUND WHEN REMOVING GAS CAP????????? (MNJack)
I don't think it's so much a vacumn as it is a build up of pressure in the tank and when you open the cap you are releasing that pressure. Gas vapor expands as the car and tank heat up and build up pressure. Thats why a nearly empty tank is much more dangerous than a full tank (gas vapor is highly explosive). :eek:
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Advanced
Joined: Mar 2002
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From: Colorado
Re: VACUUM SOUND WHEN REMOVING GAS CAP????????? (SIGNGUY)
:smash: :yesnod: Know for a fact with mine -- it's pressure. Wondered about it for years if it was hurting anything - never any adverse affect so far. I always thought the vented cap had a one way check valve (little steel ball) that allowed atmosphere to enter, but kept the gas vapor from escaping. :confused: Willing to learn something new every day...especially in this GREAT forum!! :yesnod: :chevy
Instructor
Joined: Jun 2001
Posts: 229
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From: Uxbridge MA
Re: VACUUM SOUND WHEN REMOVING GAS CAP????????? (SIGNGUY)
I recently replaced my vented cap because the original was very badly rusted and was flaking into the gas tank. Upon fillup after a long drive, I would open the cap and it would pop up because of pressure build up. There is a check valve in the center underside of the cap and I could push the valve open with a small pin. It just did not seem to open eventhough the tank was pressurized. I got tired of this gas game and drilled a 1/16" whole through the check valve in the cap. Maybe I just got a bum replacement cap.
--Andy
--Andy
Melting Slicks
Joined: Dec 2000
Posts: 3,407
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From: Carmichael CA
Re: VACUUM SOUND WHEN REMOVING GAS CAP????????? (SIGNGUY)
I don't get any pressure or vacuum...none of my cars do, and when one of them had a problem I would first suspect the gas cap, so I'd buy a new one. If it still had pressure/vacuum then I'd check the evaporation canister which plugs up sometimes. The evap canister has a replaceable filter...it whoud be replaced every 50,000 miles I think...something like that. I'm not sure if the filter is still available, you may need to get another canister. There is no other way for a pressure/vacuum problem to occur in the tank. Either the cap, or the evap canister are failing.
I've never heard of a gas cap singing, well I suppose it can just whistle cause how would it know the words?
I've never heard of a gas cap singing, well I suppose it can just whistle cause how would it know the words?
Thread Starter
Safety Car
Joined: Mar 2002
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From: Okeechobee Florida
Re: VACUUM SOUND WHEN REMOVING GAS CAP????????? (Rockn-Roll)
wer'nt all gas caps vented years ago and then went to vented in the 70's?
i wonder??? and if thats so...i wonder when it changed and why??
hhhmmmm...???
i wonder??? and if thats so...i wonder when it changed and why??
hhhmmmm...???
Thread Starter
Safety Car
Joined: Mar 2002
Posts: 4,411
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From: Okeechobee Florida
Re: VACUUM SOUND WHEN REMOVING GAS CAP????????? (SIGNGUY)
i just read this in another post concerning the vacuum canister...
The canister you are talking about (under the washer fluid) is the fuel vapor recovery system. While the engine sits the fuel bowl of the carb evaporates. The system is designed to store the fuel vapor in the canister so when you start the car it will suck the vapor into the engine and burn it instead of letting it vent to the atmosphere. It is also designed to vent the fuel tank though the intake manifold. Removing it will make your garage stink and could cause pressure (or vacuum) to build in the fuel tank.
could the cap be alright and the canister be the culprit????????
OR...is this normal and we're all wasting our time with this post??
i REALLY would like to know as im sure you guys would too... :)
The canister you are talking about (under the washer fluid) is the fuel vapor recovery system. While the engine sits the fuel bowl of the carb evaporates. The system is designed to store the fuel vapor in the canister so when you start the car it will suck the vapor into the engine and burn it instead of letting it vent to the atmosphere. It is also designed to vent the fuel tank though the intake manifold. Removing it will make your garage stink and could cause pressure (or vacuum) to build in the fuel tank.
could the cap be alright and the canister be the culprit????????
OR...is this normal and we're all wasting our time with this post??
i REALLY would like to know as im sure you guys would too... :)
Team Owner
Joined: Jul 1999
Posts: 65,492
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From: Orange Park Florida
Re: VACUUM SOUND WHEN REMOVING GAS CAP????????? (SIGNGUY)
OK, on the driver's side top of the tanks there is a black plastic float ball thingy designed to stop liquid flow toward the top of the thing, but allow fuel vapors to continue on to the charcoal reservoir....that black canister on the frame rail under the master cyl.....
the top valve typically has two hoses to the engine, one to open the valve with main manifold vacuum, the other larger one to pass the fumes into the carb/throttle body above or before the throttle blades, this is a large porten vacuum source...same kind of source used tor vacuum advance in later carb'd cars....
thing is, if the tank is full, and the check ball up top is closed, it's possible to build up pressure in the tank on a hot day, and keep the checl ball closed, tank builds pressure, only relief is through the gas cap then and top gasket....the whole idea was to prevent gas smells and evaporative emissions...
at any rate, the systems are old now, and of course gasoline is lots more stinky and objectionable than it used to be....so we notice it more....
thing is, strong fumes indicate rotten hoses...or worse....have to keep an eye on them.....seems that new fuel hose is much shorter lived than the old stuff used to be....
GENE
the top valve typically has two hoses to the engine, one to open the valve with main manifold vacuum, the other larger one to pass the fumes into the carb/throttle body above or before the throttle blades, this is a large porten vacuum source...same kind of source used tor vacuum advance in later carb'd cars....
thing is, if the tank is full, and the check ball up top is closed, it's possible to build up pressure in the tank on a hot day, and keep the checl ball closed, tank builds pressure, only relief is through the gas cap then and top gasket....the whole idea was to prevent gas smells and evaporative emissions...
at any rate, the systems are old now, and of course gasoline is lots more stinky and objectionable than it used to be....so we notice it more....
thing is, strong fumes indicate rotten hoses...or worse....have to keep an eye on them.....seems that new fuel hose is much shorter lived than the old stuff used to be....
GENE
Race Director
Joined: Oct 2000
Posts: 15,087
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From: central FL, near the beach.
Re: VACUUM SOUND WHEN REMOVING GAS CAP????????
Modern cars (not ours) use a PRESSURE/VACUUM cap. They can and do have either. But their cap has a relief valve for both.
I put one on my 67 ford; it can sit for months and it(pressure) keeps the carb full of gas(it used to evaporate)
I put one on my 67 ford; it can sit for months and it(pressure) keeps the carb full of gas(it used to evaporate)
Thread Starter
Safety Car
Joined: Mar 2002
Posts: 4,411
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From: Okeechobee Florida
Re: VACUUM SOUND WHEN REMOVING GAS CAP???????? (drives61)
i read this in my manual while at work today (the one that comes with the car new), under "how to fill up the gas tank"...and i quote...
"Rotate cap counterclockwise to clear the inside of the filler neck. This will allow any residual pressure to escape."
sounds like a normal thing to me...
"Rotate cap counterclockwise to clear the inside of the filler neck. This will allow any residual pressure to escape."
sounds like a normal thing to me...
