whooshing sound when removing gas cap

[Dan Raymond]

I own a 1987 Acura Integra. I've noticed that when I stop for gas and
remove the fuel cap a loud whooshing sound ensues as if a large volume
of air is suddenly being drawn into the fuel tank. Is this normal?
Does it indicate a problem that should be fixed?

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[y_p_w]

Dan Raymond wrote:
>
> I own a 1987 Acura Integra. I've noticed that when I stop for gas and
> remove the fuel cap a loud whooshing sound ensues as if a large volume
> of air is suddenly being drawn into the fuel tank. Is this normal?
> Does it indicate a problem that should be fixed?

It's normal. It's probably a vacuum developing in the tank as the
fuel is pumped. The air pressure then normalizes when you open the
gas cap. It haapens with every car in my family. I thought that
it might be gas vapor going out the other way, but I usually don't
see that visual distortion like you see from the fumes in a gas
can.

[- Philip]

> I've noticed that when I stop for gas and
>remove the fuel cap a loud whooshing sound ensues as if a large volume
>of air is suddenly being drawn into the fuel tank. Is this normal?

Odds are you have a PRESSURE build up. This happens as the your fuel warms up
from being recirculated up to the engine and back... again and again. The fuel
tank vapors are vented only when there is a light load on the engine (ported
vacuum) to the charcoal canister and then drawn into the engine. NO raw
gasoline is to allowed into the atmosphere.

NOW... when heating the fuel and the resulting pressure build up is faster than
the venting process, you will find a slightly pressurized fuel tank (the whoosh
you get while removing the fuel cap).

The phenominon is more pronounced with oxygenated fuel.

~~Philip

"Vituperation is a Usenet hallmark"

[- Philip]

> I thought that
>it might be gas vapor going out the other way, but I usually don't
>see that visual distortion like you see from the fumes in a gas
>can.

Try this: Locate the vent line on your charcoal canister that goes back to the
fuel tank. When you are ready to refuel your warm car, before removing the
cap, raise the hood and pull the fuel tank vent line at the charcoal canister.
If you feel a small amount of pressure (you'll smell gasoling too), you'll know
the 'whoosh' you hear is pressure....not vacuum.

With the event of screw-in emission fuel caps, these caps have either been non
vented or pressure/vacuum vent to atmosphere.

[Robert Hancock]

Unlikely it's a vacuum, likely a pressure buildup from fuel vapors -
normal..

--
Robert Hancock Saskatoon, SK, Canada
To email, remove "nospam" from hanc...@nospamhome.com
Home Page: http://roberthancock.netfirms.com/

"Dan Raymond" <dray...@foxvalley.net> wrote in message
news:3ac67b48...@news.foxvalley.net...

[Richard S Krause]

It's normal and it's vacuum. Gas caps used to be vented, in the days
before emissions controls. Now they aren't and the phenomenon you describe
occurs. Cars with OBDII emissions controls even monitor gas tank pressure.
If a leak is detected (such as from a loose gas cap) the SES light is
triggered.

Rich Krause

[kev...@gmail.com]

That is not normal, there is a vent valve to compensate for that.

[thekma...@gmail.com]

What has not been breached here - and should have been long
ago - is if the owner was in the habit of topping off when gassing
up at the station: 'click-thunk', 'click-thunk'. That action could
contribute to his 'whooshing' experience.

[The Real Bev]

I hear no whooshing sounds and I always do three topoff click-thunks --
even then I don't approach spillage level.

--
Cheers, Bev
You need only three tools: WD-40, duct tape and a hammer. If it doesn't
move and it should, use WD-40. If it moves and shouldn't, use duct tape.
If you can't fix it with a hammer you've got an electrical problem.

[Steve W.]

The Real Bev wrote:
> On 04/01/2019 04:57 PM, thekma...@gmail.com wrote:
>> What has not been breached here - and should have been long
>> ago - is if the owner was in the habit of topping off when gassing
>> up at the station: 'click-thunk', 'click-thunk'. That action could
>> contribute to his 'whooshing' experience.
>
> I hear no whooshing sounds and I always do three topoff click-thunks --
> even then I don't approach spillage level.
>

On anything newer than 2000 that is a good way to wipe out the charcoal
canister. Fuel goes down the vent line attached to the side of the fill
pipe and drowns the canister.

--
Steve W.

[The Real Bev]

How far from the top is the vent line attached? LA County filler tube, BTW.


--
Cheers, Bev
"At the core of liberalism is the spoiled child,
miserable, as all spoiled children are, unsatisfied,
demanding, ill-disciplined, despotic and useless.
Liberalism is a philosophy of sniveling brats."
PJ O'Rourke

[Steve W.]

The Real Bev wrote:
> On 04/03/2019 12:24 AM, Steve W. wrote:
>> The Real Bev wrote:
>>> On 04/01/2019 04:57 PM, thekma...@gmail.com wrote:
>>>> What has not been breached here - and should have been long
>>>> ago - is if the owner was in the habit of topping off when gassing
>>>> up at the station: 'click-thunk', 'click-thunk'. That action could
>>>> contribute to his 'whooshing' experience.
>>> I hear no whooshing sounds and I always do three topoff click-thunks --
>>> even then I don't approach spillage level.
>>>
>> On anything newer than 2000 that is a good way to wipe out the charcoal
>> canister. Fuel goes down the vent line attached to the side of the fill
>> pipe and drowns the canister.
>
> How far from the top is the vent line attached? LA County filler tube, BTW.
>
>

Most are just below the flapper valve in the filler neck.

--
Steve W.

[The Real Bev]

From what I read, that closes when fuel gets high enough in the neck,
right? I would assume that it's located to prevent overflow...

What actually makes the nozzle shut off? Upon occasion I've put in at
least another gallon after the first automatic click-thunk shutoff. I
like to fill it as full as possible -- you never can tell when you'll
just be able to make it to the Mesquite station on fumes because it was
too hard to find a cheap gas station in Vegas.

--
Cheers, Bev
"To liberals, building a wall across the Mexican border is a
violation of the Voting Rights Act." -- Ann Coulter

[thekma...@gmail.com]

Steve W wrote: "newer than 2000 that is a good way to wipe out the charcoal

canister. Fuel goes down the vent line attached to the side of the fill
pipe and drowns the canister. "

^This!!^ Why I haven't topped off in fifteen years!

Of course, you might as well be explaining it
to a wall - present "Real" company notwithstanding.

[Steve W.]

The Real Bev wrote:
> On 04/04/2019 07:14 PM, Steve W. wrote:
>> The Real Bev wrote:
>>> On 04/03/2019 12:24 AM, Steve W. wrote:
>>>> The Real Bev wrote:
>>>>> On 04/01/2019 04:57 PM, thekma...@gmail.com wrote:
>>>>>> What has not been breached here - and should have been long
>>>>>> ago - is if the owner was in the habit of topping off when gassing
>>>>>> up at the station: 'click-thunk', 'click-thunk'. That action could
>>>>>> contribute to his 'whooshing' experience.
>>>>> I hear no whooshing sounds and I always do three topoff click-thunks --
>>>>> even then I don't approach spillage level.
>>>>>
>>>> On anything newer than 2000 that is a good way to wipe out the charcoal
>>>> canister. Fuel goes down the vent line attached to the side of the fill
>>>> pipe and drowns the canister.
>>> How far from the top is the vent line attached? LA County filler tube, BTW.
>> Most are just below the flapper valve in the filler neck.
>
> From what I read, that closes when fuel gets high enough in the neck,
> right? I would assume that it's located to prevent overflow...
>
> What actually makes the nozzle shut off? Upon occasion I've put in at
> least another gallon after the first automatic click-thunk shutoff. I
> like to fill it as full as possible -- you never can tell when you'll
> just be able to make it to the Mesquite station on fumes because it was
> too hard to find a cheap gas station in Vegas.
>

No the flap I'm talking about is the one the fuel fill nozzle opens just
below the cap. That stays open while filling to allow vapor to pass the
pump nozzle. It acts as a valve to keep debris out as well as a
restriction to keep people from using the wrong pump to fill the tank
(diesel usually has a larger nozzle diameter that won't fit) Plus it
helps prevent the fuel from pouring out at the instant the nozzle trips off.

The nozzle shuts off when it detects a change in vacuum inside the
handle. If you look inside a nozzle you will see a small hole or tube
inside. While filling the gas flow over the hole/tube creates a vacuum.
While gas is flowing that vacuum doesn't do much. However as soon as the
tank is full the gas backs up in the fill neck. That blocks the
tube/hole and the instant lack of vacuum trips a small diaphragm inside
the filler handle which stops the fuel.

--
Steve W.

[The Real Bev]

I first saw those when unleaded became the only option (remember smog
heads?) and thought it was just to restrict the size of the nozzle that
could be inserted.

> The nozzle shuts off when it detects a change in vacuum inside the
> handle. If you look inside a nozzle you will see a small hole or tube
> inside. While filling the gas flow over the hole/tube creates a vacuum.
> While gas is flowing that vacuum doesn't do much. However as soon as the
> tank is full the gas backs up in the fill neck. That blocks the
> tube/hole and the instant lack of vacuum trips a small diaphragm inside
> the filler handle which stops the fuel.

Given my sinful triple-top-up procedure, I've observed that different
pumps have different levels of stoppage. Is there an actual standard?

--
Cheers, Bev
"The almost universal access to higher education here in the US has
ruined a lot of potentially good manual laborers." -- Bob Hunt

[Steve W.]

Most of the time the "standard" is simply that it shuts off before it
sprays you with fuel.
It all depends on the flow rate from the pump and how well the fuel tank
accepts high flow of fuel. Get a real fast pump and try feeding some of
the imports where the fuel neck is just a hair larger than a garden hose
and it can be interesting. Most vehicles have multiple restrictions in
the filler neck and tank as well. Things like a screen to prevent
siphoning or the rollover ball in the top of the tank or the vapor vent
from the tank being small.

--
Steve W.

[allise...@gmail.com]

If you get a Check fuel filter light? www.arcamax.com/business/businessnews/s-2197190