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[GMCnet] In tank fuel pumps, or external pumps. [message #316290] Wed, 19 April 2017 22:36 Go to next message
BobDunahugh is currently offline  BobDunahugh   United States
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Registered: October 2010
Location: Cedar Rapids, IA
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Both ways have their own good, and bad points. Pulling tanks isn't a real big deal. It's the getting the GMC high enough to do it. And if your on the road. That really gets more complicated. I'm going to put in 1 pump per tank. One way, or the other. And take the tank selector valve out. So since I'm thinking of external pumps mostly for simply of installation, and access for repair. What's the advantages of the in tank installation? Bob Dunahugh 78 Royale
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Re: [GMCnet] In tank fuel pumps, or external pumps. [message #316292 is a reply to message #316290] Wed, 19 April 2017 22:41 Go to previous messageGo to next message
USAussie is currently offline  USAussie   United States
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Registered: July 2007
Location: Sydney, Australia
Karma: 38
Senior Member
If you cut two "port holes" in the floor replacing a defective in-tank fuel
pump becomes an easier job than an external one, you can do it with the roof
A/C running! :-)

Regards,
Rob M.
The Pedantic Mechanic
USAussie - Downunder
AUS '75 Avion - The Blue Streak TZE365V100428
USA '75 Avion - Double Trouble TZE365V100426
USA '77 Kingsley - TZE 267V100808

-----Original Message-----
From: Gmclist [mailto:gmclist-bounces-AT-list-DOT-gmcnet-DOT-org] On Behalf Of Bob
Dunahugh
Sent: Wednesday, April 19, 2017 10:37 PM
To: gmclist-AT-list-DOT-gmcnet-DOT-org
Subject: [GMCnet] In tank fuel pumps, or external pumps.

Both ways have their own good, and bad points. Pulling tanks isn't a real
big deal. It's the getting the GMC high enough to do it. And if your on the
road. That really gets more complicated. I'm going to put in 1 pump per
tank. One way, or the other. And take the tank selector valve out. So since
I'm thinking of external pumps mostly for simply of installation, and access
for repair. What's the advantages of the in tank installation? Bob Dunahugh
78 Royale
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Regards, Rob M. (USAussie) The Pedantic Mechanic Sydney, Australia '75 Avion - AUS - The Blue Streak TZE365V100428 '75 Avion - USA - Double Trouble TZE365V100426
Re: [GMCnet] In tank fuel pumps, or external pumps. [message #316295 is a reply to message #316290] Wed, 19 April 2017 23:19 Go to previous messageGo to next message
A Hamilto is currently offline  A Hamilto   United States
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Registered: April 2011
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Senior Member
BobDunahugh wrote on Wed, 19 April 2017 22:36
...What's the advantages of the in tank installation? Bob Dunahugh 78 Royale
Absolute elimination of vapor lock.

It would take an act of God for the fuel to vaporize at the inlet of a submerged pump.


73 23' Sequoia 4 Sale
73 23' CanyonLands Parts Unit 4 Sale
Upper Alabama
"Every day I become more convinced that I am the only person left on the planet that recognizes nonsense for what it is."
Re: [GMCnet] In tank fuel pumps, or external pumps. [message #316296 is a reply to message #316290] Thu, 20 April 2017 00:14 Go to previous messageGo to next message
Ken Burton is currently online  Ken Burton   United States
Messages: 7959
Registered: January 2004
Location: Hebron, Indiana
Karma: 25
Senior Member

I have never experienced vapor lock on my GMC with one exception. That was my Onan quit multiple times at 100+ degrees going to GMCMI Branson last summer. Some People here have had problems boiling fuel in the tank on a GMC.

I have experienced vapor lock on a vehicle with in tanks pumps. That was at 100 + degrees in the desert on some no name road with no place to hide out of the sun until the vehicle cooled down. There wasn't a tree anywhere for miles in all directions to hide under. This vehicle has an in tank pump with the output pressure of 55 to 60 PSI. So an in tank pump is not a guarantee of no vapor lock.

After sitting out there in the sun for about an hour with the hood up, the vehicle and fuel cooled down and it restarted. I continued on my way for something like 30 or 40 miles to the next town. There I had lunch at the only restaurant and killed a few hours in town until the sun was almost set. Then I took the car to a self service car wash and cooled down everything under the hood and also the tank with spray water. After that I drove very late into the night (actually a few hundred miles to the next state) to burn off that fuel. I never had another vapor lock problem again. I never removed the gas cap to see if the fuel was boiling inthe tank.

In tank pumps while a better idea, are no guarantee against vapor lock. While killing time in that town, I stopped by the only garage and wrecker service to get his name and phone number in case I got stalled again. He told me that he tows in 3 or 4 cars a week with vapor lock off of that stretch of highway when it is around 100 degrees or better. I did not ask how he knew when to get one of them as there was no cell service out there and only one car passed me in the hour that I sat out there.


Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
Re: [GMCnet] In tank fuel pumps, or external pumps. [message #316334 is a reply to message #316296] Thu, 20 April 2017 16:49 Go to previous messageGo to next message
A Hamilto is currently offline  A Hamilto   United States
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Registered: April 2011
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Ken Burton wrote on Thu, 20 April 2017 00:14
...I have experienced vapor lock on a vehicle with in tanks pumps. That was at 100 + degrees in the desert on some no name road with no place to hide out of the sun until the vehicle cooled down. ...In tank pumps while a better idea, are no guarantee against vapor lock.
In-tank pumps are the best you are going to do. If that vehicle had a mechanical pump exterior to the tank, you would have been there with no place to hide out of the sun for several hours instead of just one.


73 23' Sequoia 4 Sale
73 23' CanyonLands Parts Unit 4 Sale
Upper Alabama
"Every day I become more convinced that I am the only person left on the planet that recognizes nonsense for what it is."

[Updated on: Thu, 20 April 2017 16:49]

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Re: [GMCnet] In tank fuel pumps, or external pumps. [message #316339 is a reply to message #316290] Thu, 20 April 2017 17:17 Go to previous messageGo to next message
Glenn is currently offline  Glenn   Canada
Messages: 82
Registered: February 2004
Location: Northwestern Ontario
Karma: 1
Member
Access on the frame rail is good but not on the side of the interstate as the pumps are most likely on the drivers side. In tank pumps with access from the inside ports have worked for us with no vapour lock or pump failure in 40K. Have on the other hand had the opportunity to change frame rail pumps while my lovely gal watched to make sure my legs did not protrude into the oncoming trucks etc. Also of note the trucks were travelling in excess of 70mph and buffeting the mh as I was underneath. Not fun

HTH.........
Glenn
76 Glensbroke
Re: [GMCnet] In tank fuel pumps, or external pumps. [message #316350 is a reply to message #316290] Thu, 20 April 2017 18:38 Go to previous messageGo to next message
kerry pinkerton is currently offline  kerry pinkerton   United States
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Registered: July 2012
Location: Harvest, Al
Karma: 18
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I went with two external pumps as previously described. Pumps push better than suck but the pumps are about as close to the tank as possible. If I was going to use internal tanks, I'd definitely cut access holes in the floor and have a screw down cover that I could remove. That said, the odds of BOTH pumps failing is remote and as long as you never get below 1/2 tank, you should be able to get out of trouble.

Perhaps someone should investigate putting a cooling coil inside the fuel tanks??? :0


Kerry Pinkerton - North Alabama 77 Eleganza II, 403CI, Manny Brakes, 1 ton, tranny, lots of aluminum goodies. http://www.bdub.net/pinkerton/ '03 Fleetwood Discovery 39L
Re: [GMCnet] In tank fuel pumps, or external pumps. [message #316360 is a reply to message #316350] Thu, 20 April 2017 22:20 Go to previous messageGo to next message
Ken Burton is currently online  Ken Burton   United States
Messages: 7959
Registered: January 2004
Location: Hebron, Indiana
Karma: 25
Senior Member

How about using a cheap ethanol / gasoline separator. (I have never seen one.) That would bring the RVP back to what we had before this EPA madness. With the separator you could dump the excess ethanol in the exhaust just like the thermosan units, or you could mix it with water and put it in the black tank for later disposal.

We have guys at the airport doing this separation with water but it is a standalone operation. We have never found a use for the removed ethanol and water mixture, so it just gets dumped. I'm sure the EPA is not happy about that but they are the ones who caused the problem in the first place.


Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
Re: [GMCnet] In tank fuel pumps, or external pumps. [message #316363 is a reply to message #316290] Fri, 21 April 2017 00:24 Go to previous messageGo to next message
BobDunahugh is currently offline  BobDunahugh   United States
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Registered: October 2010
Location: Cedar Rapids, IA
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Senior Member

A hole in the floor is fine if you have carpet. But a vinyl, or other hard surfaces to me is an other subject. In our burned 78 GMC. I had the electric pump just at the front of the tanks. I never had vapor lock. Even being in Arizona during a hot week in July. With my tanks being at 115 degrees. And with the amount of gas coming out of those tanks to cool those gas lines. Apparently gas got to my carb before the gas got to a temp to create a vapor lock condition. So I just don't see how moving the pumps just outside the tanks can help reduce vapor lock to any measureable degree. That 115 degree gas might hit the external pumps at 118 degrees. That's along way from vapor lock temps. I don't see in tank pump as a bad idea. I just would like to find a reason to justify the extra work for me. Bob Dunahugh


Both ways have their own good, and bad points. Pulling tanks isn't a real big deal. It's the getting the GMC high enough to do it. And if your on the road. That really gets more complicated. I'm going to put in 1 pump per tank. One way, or the other. And take the tank selector valve out. So since I'm thinking of external pumps mostly for simply of installation, and access for repair. What's the advantages of the in tank installation? Bob Dunahugh 78 Royale
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Re: [GMCnet] In tank fuel pumps, or external pumps. [message #316365 is a reply to message #316363] Fri, 21 April 2017 05:32 Go to previous messageGo to next message
USAussie is currently offline  USAussie   United States
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Location: Sydney, Australia
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Bob,

How about a deck plate that sits flush with a hardwood or vinyl floor
covered with a custom fit bound carpet that fits the area perfectly.

You have easy access to the fuel tank senders / pickups and a carpet you can
remove and clean.

They come in brass and stainless steel so if you have a wood floor and don't
want a carpet you leave them exposed, they do that on hi end yachts.

http://www.ebay.com/sch/i.html?_from=R40&_trksid=p2047675.m570.l1313.TR11.TR
C1.A0.H0.Xdeck+plate.TRS0&_nkw=deck+plate&_sacat=0

Regards,
Rob M.
The Pedantic Mechanic
USAussie - Downunder
AUS '75 Avion - The Blue Streak TZE365V100428
USA '75 Avion - Double Trouble TZE365V100426
USA '77 Kingsley - TZE 267V100808

-----Original Message-----
From: Gmclist [mailto:gmclist-bounces-AT-list-DOT-gmcnet-DOT-org] On Behalf Of Bob
Dunahugh
Sent: Friday, April 21, 2017 12:24 AM
To: gmclist-AT-list-DOT-gmcnet-DOT-org
Subject: Re: [GMCnet] In tank fuel pumps, or external pumps.


A hole in the floor is fine if you have carpet. But a vinyl, or other hard
surfaces to me is an other subject. In our burned 78 GMC. I had the
electric pump just at the front of the tanks. I never had vapor lock. Even
being in Arizona during a hot week in July. With my tanks being at 115
degrees. And with the amount of gas coming out of those tanks to cool those
gas lines. Apparently gas got to my carb before the gas got to a temp to
create a vapor lock condition. So I just don't see how moving the pumps just
outside the tanks can help reduce vapor lock to any measureable degree. That
115 degree gas might hit the external pumps at 118 degrees. That's along way
from vapor lock temps. I don't see in tank pump as a bad idea. I just would
like to find a reason to justify the extra work for me. Bob Dunahugh


Both ways have their own good, and bad points. Pulling tanks isn't a real
big deal. It's the getting the GMC high enough to do it. And if your on the
road. That really gets more complicated. I'm going to put in 1 pump per
tank. One way, or the other. And take the tank selector valve out. So since
I'm thinking of external pumps mostly for simply of installation, and access
for repair. What's the advantages of the in tank installation? Bob Dunahugh
78 Royale
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Regards, Rob M. (USAussie) The Pedantic Mechanic Sydney, Australia '75 Avion - AUS - The Blue Streak TZE365V100428 '75 Avion - USA - Double Trouble TZE365V100426
Re: [GMCnet] In tank fuel pumps, or external pumps. [message #316366 is a reply to message #316365] Fri, 21 April 2017 06:27 Go to previous messageGo to next message
kstockwell is currently offline  kstockwell   United States
Messages: 177
Registered: May 2016
Location: Putney VT
Karma: 0
Senior Member
OK, I don't fill up at 1/2 a tank, I go below that. Like this spring when I unwinterized the low fuel light was occasionally coming on, drove 8 miles and put 41 gallons in the rig

What are the concerns with going below 1/2 a tank (and I assume you mean 1/2 a tank when level)

-kelly


PS one thing the PO did just before I got the rig (after I agreed to buy it) was put in an additional tank (exterior). He is a great PO


1978 Kingsley Putney VT

[Updated on: Fri, 21 April 2017 06:27]

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Re: [GMCnet] In tank fuel pumps, or external pumps. [message #316372 is a reply to message #316366] Fri, 21 April 2017 08:02 Go to previous messageGo to next message
lqqkatjon is currently offline  lqqkatjon   United States
Messages: 1392
Registered: October 2010
Location: St. Cloud, MN
Karma: 3
Senior Member
Normal world, nothing but greater chance of running out of gas if you are not close to gas station.

There is slight bit of chance of getting sediment and junk off bottom of gas tank. But probably not an issue with a regular driven coach. Also if you need generator, That usually will not get gas at less then 1/4 tank. So if you need that for ac or other.


Jon Roche 75 palm beach St. Cloud, MN http://lqqkatjon.blogspot.com/
Re: [GMCnet] In tank fuel pumps, or external pumps. [message #316374 is a reply to message #316290] Fri, 21 April 2017 08:28 Go to previous messageGo to next message
Larry is currently offline  Larry   United States
Messages: 1918
Registered: January 2004
Location: Menomonie, WI
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Senior Member
A lot of us have "been there" with different ways of plumbing fuel to the engine. IMO, pumps in the tanks and all steel fuel lines is the final answer. Two tanks, two pumps. Both pumps are a back-up for the other. Either will allow you to drain...I'd guess...2/3rd s of the 50gal of fuel you can carry, meaning you can get'r home. JMHO

As far as having access holes in the floor of your coach to change the pumps, personally, I would not bother. If you put pumps in the tanks, as outlined in the Stora article, because the assembled tank unit is fairly big, (especially if you change to all steel lines) you need a lot of room around the tank hole to manipulate the assembly when inserting it into the tank. You'd have to have quite a large hole in the floor. I have a small hole (6" in dia.) to check in case of leaks or electrical issues. Dropping the tanks is not as big of a deal as made out to be. The hardest part of the whole thing is draining of the tanks and where to put all of that fuel. Draining is actually relatively easy. Just hook a section of rubber fuel line to the line at the fuel rails, throttle body or a convenient spot in the fuel lines, and wire the pump to pump the fuel out. I can drop both tanks, fix and replace in a morning. .

HTH


Larry Smile
78 Royale w/500 Caddy
Menomonie, WI.
Re: [GMCnet] In tank fuel pumps, or external pumps. [message #316375 is a reply to message #316374] Fri, 21 April 2017 09:22 Go to previous messageGo to next message
James Hupy is currently offline  James Hupy   United States
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Senior Member
It is not a problem, IF you are in a shop with a hard floor WHEN the pump
(s) fail and you need to drop the tanks. Carefully read the submission by
Glen Gregory about fixing fuel pumps alongside a busy highway while semi's
blow past at 70 per. Not a very safe way to spend an afternoon.
Jim Hupy
Salem, Or
78 GMC ROYALE 403

On Apr 21, 2017 6:28 AM, "Larry" wrote:

> A lot of us have "been there" with different ways of plumbing fuel to the
> engine. IMO, pumps in the tanks and all steel fuel lines is the final
> answer. Two tanks, two pumps. Both pumps are a back-up for the other.
> Either will allow you to drain...I'd guess...2/3rd s of the 50gal of fuel
> you
> can carry, meaning you can get'r home. JMHO
>
> As far as having access holes in the floor of your coach to change the
> pumps, personally, I would not bother. If you put pumps in the tanks, as
> outlined in the Stora article, because the assembled tank unit is fairly
> big, (especially if you change to all steel lines) you need a lot of room
> around the tank hole to manipulate the assembly when inserting it into the
> tank. You'd have to have quite a large hole in the floor. I have a small
> hole (6" in dia.) to check in case of leaks or electrical issues.
> Dropping the tanks is not as big of a deal as made out to be. The hardest
> part of
> the whole thing is draining of the tanks and where to put all of that
> fuel. Draining is actually relatively easy. Just hook a section of rubber
> fuel
> line to the line at the fuel rails, throttle body or a convenient spot in
> the fuel lines, and wire the pump to pump the fuel out. I can drop both
> tanks, fix and replace in a morning. .
>
> HTH
>
> --
> Larry
> 78 Royale w/500 Caddy
> Menomonie, WI.
>
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Re: [GMCnet] In tank fuel pumps, or external pumps. [message #316376 is a reply to message #316375] Fri, 21 April 2017 09:35 Go to previous messageGo to next message
jimk is currently offline  jimk   United States
Messages: 4123
Registered: July 2006
Location: Belmont, CA
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Senior Member
I take the stand that when the in tank pump goes out, the other inline pump
will work.

On Fri, Apr 21, 2017 at 7:22 AM, James Hupy wrote:

> It is not a problem, IF you are in a shop with a hard floor WHEN the pump
> (s) fail and you need to drop the tanks. Carefully read the submission by
> Glen Gregory about fixing fuel pumps alongside a busy highway while semi's
> blow past at 70 per. Not a very safe way to spend an afternoon.
> Jim Hupy
> Salem, Or
> 78 GMC ROYALE 403
>
> On Apr 21, 2017 6:28 AM, "Larry" wrote:
>
>> A lot of us have "been there" with different ways of plumbing fuel to the
>> engine. IMO, pumps in the tanks and all steel fuel lines is the final
>> answer. Two tanks, two pumps. Both pumps are a back-up for the other.
>> Either will allow you to drain...I'd guess...2/3rd s of the 50gal of fuel
>> you
>> can carry, meaning you can get'r home. JMHO
>>
>> As far as having access holes in the floor of your coach to change the
>> pumps, personally, I would not bother. If you put pumps in the tanks, as
>> outlined in the Stora article, because the assembled tank unit is fairly
>> big, (especially if you change to all steel lines) you need a lot of room
>> around the tank hole to manipulate the assembly when inserting it into
> the
>> tank. You'd have to have quite a large hole in the floor. I have a
> small
>> hole (6" in dia.) to check in case of leaks or electrical issues.
>> Dropping the tanks is not as big of a deal as made out to be. The hardest
>> part of
>> the whole thing is draining of the tanks and where to put all of that
>> fuel. Draining is actually relatively easy. Just hook a section of rubber
>> fuel
>> line to the line at the fuel rails, throttle body or a convenient spot in
>> the fuel lines, and wire the pump to pump the fuel out. I can drop both
>> tanks, fix and replace in a morning. .
>>
>> HTH
>>
>> --
>> Larry
>> 78 Royale w/500 Caddy
>> Menomonie, WI.
>>
>> _______________________________________________
>> GMCnet mailing list
>> Unsubscribe or Change List Options:
>> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>>
> _______________________________________________
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>



--
Jim Kanomata
Applied/GMC, Fremont,CA
jimk-AT-appliedairfilters-DOT-com
http://www.appliedgmc.com
1-800-752-7502
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Jim Kanomata
Applied/GMC
jimk-AT-appliedairfilters-DOT-com
www.appliedgmc.com
1-800-752-7502
Re: [GMCnet] In tank fuel pumps, or external pumps. [message #316377 is a reply to message #316363] Fri, 21 April 2017 09:42 Go to previous messageGo to next message
BobDunahugh is currently offline  BobDunahugh   United States
Messages: 1338
Registered: October 2010
Location: Cedar Rapids, IA
Karma: 7
Senior Member

To get 87 octane gas to boil. You need temps that are approaching 200 degrees. Those are temps that you can't touch. I've had an electric fuel pump near my tanks fail on a day when the temp was near 100. The tank, pump, and frame were no were near that. Maybe 125 at most. That day I was pulling my enclosed trailer. GVW was at about 21,000 lbs. Anyone in the Southwest. Check the temps on days like that. Gas just can't boil back there. Even on a hot day.




A hole in the floor is fine if you have carpet. But a vinyl, or other hard surfaces to me is an other subject. In our burned 78 GMC. I had the electric pump just at the front of the tanks. I never had vapor lock. Even being in Arizona during a hot week in July. With my tanks being at 115 degrees. And with the amount of gas coming out of those tanks to cool those gas lines. Apparently gas got to my carb before the gas got to a temp to create a vapor lock condition. So I just don't see how moving the pumps just outside the tanks can help reduce vapor lock to any measureable degree. That 115 degree gas might hit the external pumps at 118 degrees. That's along way from vapor lock temps. I don't see in tank pump as a bad idea. I just would like to find a reason to justify the extra work for me. Bob Dunahugh


Both ways have their own good, and bad points. Pulling tanks isn't a real big deal. It's the getting the GMC high enough to do it. And if your on the road. That really gets more complicated. I'm going to put in 1 pump per tank. One way, or the other. And take the tank selector valve out. So since I'm thinking of external pumps mostly for simply of installation, and access for repair. What's the advantages of the in tank installation? Bob Dunahugh 78 Royale
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Re: [GMCnet] In tank fuel pumps, or external pumps. [message #316379 is a reply to message #316377] Fri, 21 April 2017 10:21 Go to previous messageGo to next message
emerystora is currently offline  emerystora   United States
Messages: 4070
Registered: January 2004
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Senior Member
Gasoline does not have to boil to cause vapor lock. It just has to vaporize. Liquids can change to a vapor well below their boiling point. Just look at the roads after a rain. The water dries up from the road by changing to a vapor into the air and yet the surface of the road is not at 212 degrees, the boiling point of water.

I had an external electric pump just outside my tanks but still got vapor lock at times, especially at the high altitudes here in Colorado.

I installed the in-tank pumps in 2010 and have not had any vapor lock since. They now have about 8 years on them and no failures. I probably put more miles on each year than most of you. I have gone to Michigan and to Florida each year plus most of the GMCMI conventions.

My feeling is that if a pump should ever fail on a trip I can get by with one pump or I could easily mount a pump outside the frame rail where it used to be and pull through the failed pump if I am 2000 miles from home and don't want to fill as often.

It will be interesting to see how many years the pumps last.

The in-tank pump in my 1973 Jeep Grand Cherokee never failed in the 20+ years I owned it (over 200,000 miles) so in-tank pumps seem to last a long time. I think people's fears of pump failure are overrated. Of course it can happen but it's a risk I can accept. My pumps are Airtex. I would not buy cheaper pumps.

Emery Stora
77 Kingsley
Frederick, CO

> On Apr 21, 2017, at 8:42 AM, Bob Dunahugh wrote:
>
>
> To get 87 octane gas to boil. You need temps that are approaching 200 degrees. Those are temps that you can't touch. I've had an electric fuel pump near my tanks fail on a day when the temp was near 100. The tank, pump, and frame were no were near that. Maybe 125 at most. That day I was pulling my enclosed trailer. GVW was at about 21,000 lbs. Anyone in the Southwest. Check the temps on days like that. Gas just can't boil back there. Even on a hot day.
>
>
>
>
> A hole in the floor is fine if you have carpet. But a vinyl, or other hard surfaces to me is an other subject. In our burned 78 GMC. I had the electric pump just at the front of the tanks. I never had vapor lock. Even being in Arizona during a hot week in July. With my tanks being at 115 degrees. And with the amount of gas coming out of those tanks to cool those gas lines. Apparently gas got to my carb before the gas got to a temp to create a vapor lock condition. So I just don't see how moving the pumps just outside the tanks can help reduce vapor lock to any measureable degree. That 115 degree gas might hit the external pumps at 118 degrees. That's along way from vapor lock temps. I don't see in tank pump as a bad idea. I just would like to find a reason to justify the extra work for me. Bob Dunahugh
>
>
> Both ways have their own good, and bad points. Pulling tanks isn't a real big deal. It's the getting the GMC high enough to do it. And if your on the road. That really gets more complicated. I'm going to put in 1 pump per tank. One way, or the other. And take the tank selector valve out. So since I'm thinking of external pumps mostly for simply of installation, and access for repair. What's the advantages of the in tank installation? Bob Dunahugh 78 Royale
> _______________________________________________
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Re: [GMCnet] In tank fuel pumps, or external pumps. [message #316381 is a reply to message #316377] Fri, 21 April 2017 10:32 Go to previous messageGo to next message
Matt Colie is currently offline  Matt Colie   United States
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Registered: March 2007
Location: S.E. Michigan
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Senior Member
BobDunahugh wrote on Fri, 21 April 2017 10:42

To get 87 octane gas to boil. You need temps that are approaching 200 degrees. Those are temps that you can't touch. I've had an electric fuel pump near my tanks fail on a day when the temp was near 100. The tank, pump, and frame were no were near that. Maybe 125 at most. That day I was pulling my enclosed trailer. GVW was at about 21,000 lbs. Anyone in the Southwest. Check the temps on days like that. Gas just can't boil back there. Even on a hot day.

Bob,

You are stuck on soft ground....
You don't need the fuel to "boil" to get vapor lock. All you need is the local conditions inside the fuel lines to get below the vapor pressure of any of the myriad of components of that fuel. That component will flash to vapor. As soon as that happens, the pump can't get a grip on the fuel and the game is over.

Matt


Matt & Mary Colie - '73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Still Loving OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Twixt A2 and Detroit
Re: [GMCnet] In tank fuel pumps, or external pumps. [message #316382 is a reply to message #316379] Fri, 21 April 2017 10:30 Go to previous messageGo to next message
emerystora is currently offline  emerystora   United States
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Registered: January 2004
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That should have read 1993 Jeep, not 1973.

Emery Stora

> On Apr 21, 2017, at 9:21 AM, Emery Stora wrote:
>
> Gasoline does not have to boil to cause vapor lock. It just has to vaporize. Liquids can change to a vapor well below their boiling point. Just look at the roads after a rain. The water dries up from the road by changing to a vapor into the air and yet the surface of the road is not at 212 degrees, the boiling point of water.
>
> I had an external electric pump just outside my tanks but still got vapor lock at times, especially at the high altitudes here in Colorado.
>
> I installed the in-tank pumps in 2010 and have not had any vapor lock since. They now have about 8 years on them and no failures. I probably put more miles on each year than most of you. I have gone to Michigan and to Florida each year plus most of the GMCMI conventions.
>
> My feeling is that if a pump should ever fail on a trip I can get by with one pump or I could easily mount a pump outside the frame rail where it used to be and pull through the failed pump if I am 2000 miles from home and don't want to fill as often.
>
> It will be interesting to see how many years the pumps last.
>
> The in-tank pump in my 1973 Jeep Grand Cherokee never failed in the 20+ years I owned it (over 200,000 miles) so in-tank pumps seem to last a long time. I think people's fears of pump failure are overrated. Of course it can happen but it's a risk I can accept. My pumps are Airtex. I would not buy cheaper pumps.
>
> Emery Stora
> 77 Kingsley
> Frederick, CO


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Re: [GMCnet] In tank fuel pumps, or external pumps. [message #316383 is a reply to message #316377] Fri, 21 April 2017 10:29 Go to previous messageGo to previous message
James Hupy is currently offline  James Hupy   United States
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Vapor lock occurs at a FAR LOWER TEMPERATURE THAN BOILING in a
non-pressurized container like a GMC MOTOR HOME FUEL SYSTEM. Depending upon
atmospheric pressure and temperature, whether you are using winter or
summer blend, and about a Jillion other variables. Anytime bubbles form in
gasoline, you have the potential for vapor lock. Aeromatic components of
hydrocarbon fuels will enter the atmosphere at -20° farenheit or lower.
What vapor lock is, is an inability to pump fuel through a line
because the non liquid gasses contained within bubbles in liquid fuel,
compress with pump pressure instead of travel through the line. This can
happen anytime bubbles are present in fuel.
How do you prevent bubbles from forming in liquid fuels? Blend in some
anti-foaming agents, pressurize the fuel system, eliminate aromatic
components from fuel stocks, chill the fuel, pump from behind the fuel
stream rather than sucking it through, eliminate all sources of cavitation
within the system, prevent air or other gasses from mixing into the fuel
stream, and there are other ways as well. Pick the methods that we can
accomplish, and that narrows the field a bit. In-tank pumps, we can do
that. Eliminate air infringement into our systems, we can do that, you get
the idea.
ORDINARY PRECAUTIONS are, keep a large fuel supply in your tanks, use
summer blended fuels, use fresh fuels from major brand volume dealers,
drive early in the day when it is cooler, fill up early in the day. That's
what I do. Don't run on the fumes, you are asking for fuel delivery
problems if you do it.
Personally, I have a Quadra jet carb on a stock iron manifold without
blocked exhaust crossovers, a nearly stock 403 Olds with Thorley headers
into two MagnaFlow mufflers, y-pipe and stock diameter exhaust pipe. I have
dropped my tanks years ago, replaced all hoses with Gates barrier hose,
replaced the original selector valve, and run an in-line metal fuel filter
and Carter 4070 electric pump. Yes, I have had vapor lock.
Jim Hupy
Salem, Or
78 GMC ROYALE 403

On Apr 21, 2017 7:43 AM, "Bob Dunahugh" wrote:

>
> To get 87 octane gas to boil. You need temps that are approaching 200
> degrees. Those are temps that you can't touch. I've had an electric fuel
> pump near my tanks fail on a day when the temp was near 100. The tank,
> pump, and frame were no were near that. Maybe 125 at most. That day I was
> pulling my enclosed trailer. GVW was at about 21,000 lbs. Anyone in the
> Southwest. Check the temps on days like that. Gas just can't boil back
> there. Even on a hot day.
>
>
>
>
> A hole in the floor is fine if you have carpet. But a vinyl, or other hard
> surfaces to me is an other subject. In our burned 78 GMC. I had the
> electric pump just at the front of the tanks. I never had vapor lock. Even
> being in Arizona during a hot week in July. With my tanks being at 115
> degrees. And with the amount of gas coming out of those tanks to cool those
> gas lines. Apparently gas got to my carb before the gas got to a temp to
> create a vapor lock condition. So I just don't see how moving the pumps
> just outside the tanks can help reduce vapor lock to any measureable
> degree. That 115 degree gas might hit the external pumps at 118 degrees.
> That's along way from vapor lock temps. I don't see in tank pump as a bad
> idea. I just would like to find a reason to justify the extra work for
> me. Bob Dunahugh
>
>
> Both ways have their own good, and bad points. Pulling tanks isn't a real
> big deal. It's the getting the GMC high enough to do it. And if your on the
> road. That really gets more complicated. I'm going to put in 1 pump per
> tank. One way, or the other. And take the tank selector valve out. So since
> I'm thinking of external pumps mostly for simply of installation, and
> access for repair. What's the advantages of the in tank installation? Bob
> Dunahugh 78 Royale
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