| Boiling gas vs tank venting [message #89946] |
Fri, 25 June 2010 22:45  |
midlf
Messages: 2212
Registered: July 2007
Location: SE Wisc. (Palmyra)
Karma: 1
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I have read the posts about "boiling" gas, or least vaporizing gas, causing fuel spewing from the filler when the cap is removed. Shouldn't this pressure be relieved by the emissions tank venting system?
Steve Southworth
1974 Glacier TZE064V100150 (for workin on)
1975 Transmode TZE365V100394 (parts & spares)
Palmyra WI
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| Re: [GMCnet] Boiling gas vs tank venting [message #89951 is a reply to message #89946] |
Fri, 25 June 2010 23:09  |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma: 9
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Yes. The liquid/vapor separator in the left rear wheel well should vent all
vapor through the charcoal cannister under the passenger's feet.
If that route is blocked, usually because the float in the separator is
stuck in the closed position by the distorted walls of its enclosure, the
filler cap's pressure/vacuum vent should open. According to a test I did
and published a while back, the cap should vent at about +-1 psi. Even 1
psi will probably give a pretty good "swoosh" when the cap's removed.
Another common reason for the L/V separator not doing its job is blocked
vent lines from the tanks -- squeezed shut on top of the tanks.
Those vent lines and L/V separators really do need to be checked from time
to time. They all come together at the front of the left rear wheel well
and are not difficult to reach with that wheel removed. Don't forget to
remove the gas cap before you start blowing through the 3 lines that join at
a tee there. Mine are overdue.
Ken H.
Americus, GA
'76 X-Birchaven
www.gmcwipersetc.com
On Fri, Jun 25, 2010 at 11:45 PM, Steve Southworth <midlf@centurytel.net>wrote:
>
>
> I have read the posts about "boiling" gas, or least vaporizing gas, causing
> fuel spewing from the filler when the cap is removed. Shouldn't this
> pressure be relieved by the emissions tank venting system?
> --
>
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Ken Henderson
Americus, GA
www.gmcwipersetc.com
Large Wiring Diagrams
76 X-Birchaven
76 X-Palm Beach
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| Re: Boiling gas vs tank venting [message #89954 is a reply to message #89946] |
Fri, 25 June 2010 23:36 |
Bob de Kruyff
Messages: 4260
Registered: January 2004
Location: Chandler, AZ
Karma: 1
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Senior Member |
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| midlf wrote on Fri, 25 June 2010 21:45 |
I have read the posts about "boiling" gas, or least vaporizing gas, causing fuel spewing from the filler when the cap is removed. Shouldn't this pressure be relieved by the emissions tank venting system?
|
If the system hasn't been screwed with. the primary ventilation will happen thru the charcoal cannister. unfortunately many people have disabled the system trying to compensate for poor engine vacuum levels. The secondary ventilation is thru the gas cap at 1 to 1.5 psi. Also, contrary to coomon lore, the vapor seperator has always been availble under the original p/n from most Corvette parts suppliers
Bob de Kruyff
78 Eleganza
Chandler, AZ
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| Re: [GMCnet] Boiling gas vs tank venting [message #89957 is a reply to message #89951] |
Sat, 26 June 2010 00:06 |
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ljdavick
Messages: 3548
Registered: March 2007
Location: Fremont, CA
Karma: -3
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Senior Member |
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Vent lines can also become clogged from vapor crystalizing in the
lines, if I remember Arch's Lon ago post correctly.
Ljdavick at comcast.net
On Jun 25, 2010, at 9:09 PM, Ken Henderson <hend4800@bellsouth.net>
wrote:
> Yes. The liquid/vapor separator in the left rear wheel well should
> vent all
> vapor through the charcoal cannister under the passenger's feet.
>
> If that route is blocked, usually because the float in the separator
> is
> stuck in the closed position by the distorted walls of its
> enclosure, the
> filler cap's pressure/vacuum vent should open. According to a test
> I did
> and published a while back, the cap should vent at about +-1 psi.
> Even 1
> psi will probably give a pretty good "swoosh" when the cap's removed.
>
> Another common reason for the L/V separator not doing its job is
> blocked
> vent lines from the tanks -- squeezed shut on top of the tanks.
>
> Those vent lines and L/V separators really do need to be checked
> from time
> to time. They all come together at the front of the left rear wheel
> well
> and are not difficult to reach with that wheel removed. Don't
> forget to
> remove the gas cap before you start blowing through the 3 lines that
> join at
> a tee there. Mine are overdue.
>
> Ken H.
> Americus, GA
> '76 X-Birchaven
> www.gmcwipersetc.com
>
>
> On Fri, Jun 25, 2010 at 11:45 PM, Steve Southworth <midlf@centurytel.net
> >wrote:
>
>>
>>
>> I have read the posts about "boiling" gas, or least vaporizing gas,
>> causing
>> fuel spewing from the filler when the cap is removed. Shouldn't this
>> pressure be relieved by the emissions tank venting system?
>> --
>>
> _______________________________________________
> GMCnet mailing list
> List Information and Subscription Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
_______________________________________________
GMCnet mailing list
List Information and Subscription Options:
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Larry Davick
A Mystery Machine
1976(ish) Palm Beach
Fremont, Ca
Howell EFI + EBL + Electronic Dizzy
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| Re: Boiling gas vs tank venting [message #89960 is a reply to message #89954] |
Sat, 26 June 2010 01:49 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Senior Member |
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| Bob de Kruyff wrote on Fri, 25 June 2010 23:36 |
| midlf wrote on Fri, 25 June 2010 21:45 |
I have read the posts about "boiling" gas, or least vaporizing gas, causing fuel spewing from the filler when the cap is removed. Shouldn't this pressure be relieved by the emissions tank venting system?
|
If the system hasn't been screwed with. the primary ventilation will happen thru the charcoal cannister. unfortunately many people have disabled the system trying to compensate for poor engine vacuum levels. The secondary ventilation is thru the gas cap at 1 to 1.5 psi. Also, contrary to coomon lore, the vapor seperator has always been availble under the original p/n from most Corvette parts suppliers
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Jim K. also had a "improved" one available. I assume he still has them.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: [GMCnet] Boiling gas vs tank venting [message #89962 is a reply to message #89957] |
Sat, 26 June 2010 01:53 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Senior Member |
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| ljdavick wrote on Sat, 26 June 2010 00:06 |
Vent lines can also become clogged from vapor crystalizing in the
lines, if I remember Arch's Lon ago post correctly.
Ljdavick at comcast.net
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After the hose goes up front on the left side, it connects to a small diameter steel tube and crosses over the the right side. On mine that steel tube was corroded and rusted shut. It was so bad that replacing it was the only option.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: [GMCnet] Boiling gas vs tank venting [message #90034 is a reply to message #89962] |
Sat, 26 June 2010 19:09 |
midlf
Messages: 2212
Registered: July 2007
Location: SE Wisc. (Palmyra)
Karma: 1
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Senior Member |
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| Ken Burton wrote on Sat, 26 June 2010 01:53 |
After the hose goes up front on the left side, it connects to a small diameter steel tube and crosses over the the right side. On mine that steel tube was corroded and rusted shut. It was so bad that replacing it was the only option.
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Yep, replacing that line is on my to do list.
Steve Southworth
1974 Glacier TZE064V100150 (for workin on)
1975 Transmode TZE365V100394 (parts & spares)
Palmyra WI
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| Re: Boiling gas vs tank venting [message #90088 is a reply to message #89954] |
Sun, 27 June 2010 00:36 |
midlf
Messages: 2212
Registered: July 2007
Location: SE Wisc. (Palmyra)
Karma: 1
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Senior Member |
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| Bob de Kruyff wrote on Fri, 25 June 2010 23:36 |
If the system hasn't been screwed with. the primary ventilation will happen thru the charcoal cannister. unfortunately many people have disabled the system trying to compensate for poor engine vacuum levels. The secondary ventilation is thru the gas cap at 1 to 1.5 psi. Also, contrary to common lore, the vapor separator has always been available under the original p/n from most Corvette parts suppliers
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I think sometimes we are our own worst enemies. The maintenance manual X-7425 section 8 (fuel tank) Trouble Diagnosis section covers most of the complaints mentioned in this thread. Unfortunately the cure for the problem of "high volatility fuel" is to "change brand of fuel".
One thing I noticed when I dropped my fuel tanks was the long roundabout route the fuel vapor lines took to get to the fuel/vapor separator. Also that the tank vapor lines are most definitely placed on opposite sides of the tanks from each other. GM had a reason for doing it that way. I plan to keep that arrangement when the tanks go back in. Also I will ensure that there are no droops or sags in any of the vapor or vent lines that could trap liquid and inhibit the flow of air or vapors.
Steve Southworth
1974 Glacier TZE064V100150 (for workin on)
1975 Transmode TZE365V100394 (parts & spares)
Palmyra WI
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