Home » Public Forums » GMCnet » Reversing main and Aux tank
| Reversing main and Aux tank [message #73616] |
Fri, 12 February 2010 08:16  |
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RF_Burns
Messages: 2277
Registered: June 2008
Location: S. Ontario, Canada
Karma: 3
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Senior Member |
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I have experienced the "running out of gas" while driving in a hilly area and main (rear) tank selected, so when I replaced the fuel valve I wired it so the front tank is Main.
My experience has been that since the filling pipe is connected to the front of the tanks, when going down hill the rear tank flows into the front tank. When going up hill the front tank holds its fuel as the gas moves to the back of the tank. While the coach is level, the tanks will equalize if above 1/3 full... in hilly areas the front tank tends to fill and the rear empties.
My question is has anyone else done this?
Is there any major issues with this?
Bruce Hislop
ON Canada
77PB, 455 Dick P. rebuilt, DynamicEFI EBL EFI & ESC.
1 ton front end
http://www.gmcmhphotos.com/photos/showphoto.php?photo=29001
My Staff says I never listen to them, or something like that
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| Re: [GMCnet] Reversing main and Aux tank [message #73619 is a reply to message #73616] |
Fri, 12 February 2010 09:27  |
Mr ERFisher
Messages: 7117
Registered: August 2005
Karma: 2
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Senior Member |
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This shows the problem
http://gmcmotorhome.info/tank.html
and it is even more noticeable with the Howell TBI system, since the return
from the pressure regulator tends to move gas to the AUX tank.
So I always run in the AUX position ---- no wireing changes ;>)
gene
On Fri, Feb 12, 2010 at 6:16 AM, Bruce Hislop <bruce@perthcomm.com> wrote:
>
>
> I have experienced the "running out of gas" while driving in a hilly area
> and main (rear) tank selected, so when I replaced the fuel valve I wired it
> so the front tank is Main.
>
> My experience has been that since the filling pipe is connected to the
> front of the tanks, when going down hill the rear tank flows into the front
> tank. When going up hill the front tank holds its fuel as the gas moves to
> the back of the tank. While the coach is level, the tanks will equalize if
> above 1/3 full... in hilly areas the front tank tends to fill and the rear
> empties.
>
> My question is has anyone else done this?
>
> Is there any major issues with this?
> --
> Bruce Hislop,
> S. Ontario Canada
> 77PB, 455 Dick P. rebuilt, DynamicEFI EBL EFI and ESC.
> http://www.gmcmhphotos.com/photos/showphoto.php?photo=29001
> _______________________________________________
> GMCnet mailing list
> List Information and Subscription Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>
--
Gene Fisher -- 74-23,77PB/ore/ca
“Give a man a fish; you have fed him for today --- give him a URL and
-------
http://gmcmotorhome.info/
Alternator Protection Cable
http://gmcmotorhome.info/APC.html
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| Re: Reversing main and Aux tank [message #73635 is a reply to message #73616] |
Fri, 12 February 2010 12:08 |
bobby5832708
Messages: 237
Registered: November 2006
Location: Winter Springs FL
Karma: 3
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Senior Member |
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Bruce,
I did the same thing several years ago. The front tank is used when the dash switch is in the 'main' position and the selector valve is powered off. The rear tank is used when the dash switch is in 'aux' and the selector valve is energized.
A previous owner had modified the filler system by putting a piece of pipe that looks like an ohms symbol between the tanks. This effectively isolates the two tanks from just over 3/4 tank on down to empty. In other words, starting with everything full, the fuel level goes down to between 3/4 and full on both tanks and from there on the two tanks are pretty much seperate. I've not seen this modification on any other GMC so I don't know if this sort-of-upside-down-u-shaped-pipe-thing was marketed by anyone or whether this was a one-off custom job done by or for a previous owner.
The reason I replumbed the tanks is so when dry camping I can start with about 20 gallons of fuel in the back tank for the Onan. Or sometimes after a trip the front tank is almost empty so I switch to the back tank for a moment to get up my driveway. I just like having greater control of the fuel levels in the tanks.
JWID, YMMV.
Bob Heller
2017 Winnebago 29VE
Winter Springs FL
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| Re: Reversing main and Aux tank [message #73638 is a reply to message #73616] |
Fri, 12 February 2010 12:44 |
bryant374
Messages: 563
Registered: May 2004
Location: Pleasant Valley, NY 12569
Karma: 1
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Senior Member |
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Reversing main and Aux tank Fri, 12 February 2010 09:16
RF_Burns
I have experienced the "running out of gas" while driving in a hilly area and main (rear) tank selected, so when I replaced the fuel valve I wired it so the front tank is Main.
My experience has been that since the filling pipe is connected to the front of the tanks, when going down hill the rear tank flows into the front tank. When going up hill the front tank holds its fuel as the gas moves to the back of the tank. While the coach is level, the tanks will equalize if above 1/3 full... in hilly areas the front tank tends to fill and the rear empties.
My question is has anyone else done this?
Is there any major issues with this?
Please don't anyone take offense at this.........none intended.
I am frequently surprised at the many GMC "problems" and the many "fixes" to correct them that have appeared here over the past few years. Make changes to your coach in any way you want, have a ball :^) I just haven't found many of these items to be a problem for me, but maybe I just haven't found them yet since I've only had the coach for 27 years and over 200k miles :^)
Bill Bryant
PO 1976~PB (owned 34 years)
1914 Ford (owned 70 years)
1965 Corvette (owned 39 years)
GMC Motorhome History
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| Re: [GMCnet] Reversing main and Aux tank [message #73648 is a reply to message #73619] |
Fri, 12 February 2010 17:12 |
John Wright
Messages: 118
Registered: September 2008
Karma: 0
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Senior Member |
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The simple solution is the best solution. Running in the AUX tank position
is much better than changing the wiring and making your coach special and
different from all the rest.
J.R. Wright
On Location at Florida Space Coast
On Fri, Feb 12, 2010 at 10:27 AM, Mr.erf ERFisher <mr.erfisher@gmail.com>wrote:
> This shows the problem
>
> http://gmcmotorhome.info/tank.html
>
> and it is even more noticeable with the Howell TBI system, since the return
> from the pressure regulator tends to move gas to the AUX tank.
>
> So I always run in the AUX position ---- no wireing changes ;>)
>
> gene
>
> On Fri, Feb 12, 2010 at 6:16 AM, Bruce Hislop <bruce@perthcomm.com> wrote:
>
> >
> >
> > I have experienced the "running out of gas" while driving in a hilly area
> > and main (rear) tank selected, so when I replaced the fuel valve I wired
> it
> > so the front tank is Main.
> >
> > My experience has been that since the filling pipe is connected to the
> > front of the tanks, when going down hill the rear tank flows into the
> front
> > tank. When going up hill the front tank holds its fuel as the gas moves
> to
> > the back of the tank. While the coach is level, the tanks will equalize
> if
> > above 1/3 full... in hilly areas the front tank tends to fill and the
> rear
> > empties.
> >
> > My question is has anyone else done this?
> >
> > Is there any major issues with this?
> > --
> > Bruce Hislop,
> > S. Ontario Canada
> > 77PB, 455 Dick P. rebuilt, DynamicEFI EBL EFI and ESC.
> > http://www.gmcmhphotos.com/photos/showphoto.php?photo=29001
> > _______________________________________________
> > GMCnet mailing list
> > List Information and Subscription Options:
> > http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
> >
>
>
>
> --
> Gene Fisher -- 74-23,77PB/ore/ca
> “Give a man a fish; you have fed him for today --- give him a URL and
> -------
> http://gmcmotorhome.info/
> Alternator Protection Cable
> http://gmcmotorhome.info/APC.html
> _______________________________________________
> GMCnet mailing list
> List Information and Subscription Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>
--
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| Re: [GMCnet] Reversing main and Aux tank [message #73652 is a reply to message #73619] |
Fri, 12 February 2010 18:04 |
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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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So if the tanks were actually swapped front to back, then the generator would draw from the front tank. No matter uphill or downhill the generator would always have fuel 'till the front tank got down to 1/4.
When Jim K's guys replaced my fuel lines they mentioned that my tanks had been reversed. This made no sense to me, but they're the experts and put everything back the way it ought to be. I wonder if my P.O. was more crafty than I had originally thought...
Larry Davick
The Mystery Machine.
----- Original Message -----
From: "Mr.erf ERFisher" <mr.erfisher@gmail.com>
To: gmclist@temp.gmcnet.org
Sent: Friday, February 12, 2010 7:27:20 AM GMT -08:00 US/Canada Pacific
Subject: Re: [GMCnet] Reversing main and Aux tank
This shows the problem
http://gmcmotorhome.info/tank.html
and it is even more noticeable with the Howell TBI system, since the return
from the pressure regulator tends to move gas to the AUX tank.
So I always run in the AUX position ---- no wireing changes ;>)
gene
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Larry Davick
A Mystery Machine
1976(ish) Palm Beach
Fremont, Ca
Howell EFI + EBL + Electronic Dizzy
[Updated on: Fri, 12 February 2010 18:05] Report message to a moderator |
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| Re: [GMCnet] Reversing main and Aux tank [message #73658 is a reply to message #73652] |
Fri, 12 February 2010 19:37 |
emerystora
Messages: 4442
Registered: January 2004
Karma: 13
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Senior Member |
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I don't think they are talking about physically moving the tanks. They
are only moving the electric wires that go to the fuel selector valve
and the tank level sensors so that when the dash switch in on MAIN it
will draw fuel from the front tank instead of from the rear tank.
The Onan would still draw from the rear tank.
Emery Stora
77 Kingsley
Santa Fe, NM
On Feb 12, 2010, at 5:04 PM, Larry Davick <ljdavick@comcast.net> wrote:
> So if the tanks were actually swapped front to back, then the
> generator would draw from the front tank. No matter uphill or
> downhill the generator would always have fuel 'till the front tank
> got down to 1/4.
>
> When Jim K's guys replaced my fuel lines they mentioned that my
> tanks had been reversed. This made no sense to me, but they're the
> experts and put everything back the way it out to be. I wonder if my
> P.O. was more crafty than I had originally thought...
>
> Larry Davick
> The Mystery Machine.
>
> ----- Original Message -----
> From: "Mr.erf ERFisher" <mr.erfisher@gmail.com>
> To: gmclist@temp.gmcnet.org
> Sent: Friday, February 12, 2010 7:27:20 AM GMT -08:00 US/Canada
> Pacific
> Subject: Re: [GMCnet] Reversing main and Aux tank
>
> This shows the problem
>
> http://gmcmotorhome.info/tank.html
>
> and it is even more noticeable with the Howell TBI system, since the
> return
> from the pressure regulator tends to move gas to the AUX tank.
>
> So I always run in the AUX position ---- no wireing changes ;>)
>
> gene
> _______________________________________________
> GMCnet mailing list
> List Information and Subscription Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
_______________________________________________
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List Information and Subscription Options:
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| Re: [GMCnet] Reversing main and Aux tank [message #73665 is a reply to message #73658] |
Fri, 12 February 2010 21:04 |
GMCWiperMan
Messages: 1248
Registered: December 2007
Karma: 1
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Senior Member |
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I think you're right, Emery, they're reversing the wiring. But if I were
going to do it, I'd reverse the hoses at the valve. Why? 'Cause that way
I'd still have the tank I wanted as default. That is, in the event of loss
of power to the valve my new "Main" tank would be selected.
But I prefer leaving it alone and using the switch.
I do like that inverted U in the filler line between the tanks though. Not
because I need it but because it's so brilliantly simple. :-)
Ken H.
On Fri, Feb 12, 2010 at 8:37 PM, Emery Stora <emerystora@mac.com> wrote:
> I don't think they are talking about physically moving the tanks. They
> are only moving the electric wires that go to the fuel selector valve
> and the tank level sensors so that when the dash switch in on MAIN it
> will draw fuel from the front tank instead of from the rear tank.
> The Onan would still draw from the rear tank.
>
> Emery Stora
> 77 Kingsley
> Santa Fe, NM
>
> On Feb 12, 2010, at 5:04 PM, Larry Davick <ljdavick@comcast.net> wrote:
>
> > So if the tanks were actually swapped front to back, then the
> > generator would draw from the front tank. No matter uphill or
> > downhill the generator would always have fuel 'till the front tank
> > got down to 1/4.
> >
> > When Jim K's guys replaced my fuel lines they mentioned that my
> > tanks had been reversed. This made no sense to me, but they're the
> > experts and put everything back the way it out to be. I wonder if my
> > P.O. was more crafty than I had originally thought...
> >
> > Larry Davick
> > The Mystery Machine.
> >
> > ----- Original Message -----
> > From: "Mr.erf ERFisher" <mr.erfisher@gmail.com>
> > To: gmclist@temp.gmcnet.org
> > Sent: Friday, February 12, 2010 7:27:20 AM GMT -08:00 US/Canada
> > Pacific
> > Subject: Re: [GMCnet] Reversing main and Aux tank
> >
> > This shows the problem
> >
> > http://gmcmotorhome.info/tank.html
> >
> > and it is even more noticeable with the Howell TBI system, since the
> > return
> > from the pressure regulator tends to move gas to the AUX tank.
> >
> > So I always run in the AUX position ---- no wireing changes ;>)
> >
> > gene
> > _______________________________________________
> > 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:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>
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| Re: Reversing main and Aux tank [message #73688 is a reply to message #73635] |
Sat, 13 February 2010 03:28 |
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mike miller
Messages: 3576
Registered: February 2004
Location: Hillsboro, Oregon
Karma: 0
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| bobby5832708 wrote on Fri, 12 February 2010 10:08 |
...A previous owner had modified the filler system by putting a piece of pipe that looks like an ohms symbol between the tanks. This effectively isolates the two tanks from just over 3/4 tank on down to empty. In other words, starting with everything full, the fuel level goes down to between 3/4 and full on both tanks and from there on the two tanks are pretty much seperate. I've not seen this modification on any other GMC so I don't know if this sort-of-upside-down-u-shaped-pipe-thing was marketed by anyone or whether this was a one-off custom job done by or for a previous owner. ...
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Bob,
Any chance of getting a picture? Or at least measurements?
This sounds like the best idea I have heard of for the fuel filling system. It could be a good product for someone to make into a kit.
Mike Miller -- Hillsboro, OR -- on the Black list
(#2)`78 23' Birchaven Rear Bath -- (#3)`77 23' Birchaven Side Bath
More Sidekicks than GMC's and a late model Malibu called 'Boo'
http://m000035.blogspot.com
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| Re: Reversing main and Aux tank [message #73690 is a reply to message #73688] |
Sat, 13 February 2010 03:34 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Senior Member |
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I would rather just put a check valve in there. I do not know what diameter you would need but they make 1.25" brass ones for sump pumps.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: Reversing main and Aux tank [message #73705 is a reply to message #73616] |
Sat, 13 February 2010 08:49 |
bobby5832708
Messages: 237
Registered: November 2006
Location: Winter Springs FL
Karma: 3
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Senior Member |
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What I did was swap the 2 fuel lines coming from the tanks at the selector valve and then, to make the gauge read the proper tank, swap the 2 gauge sender wires on the dashboard switch. That's it. Total time was probably under 1/2 hour.
Mike, I will try to get a picture of the filler pipe in the next few days. Due to global warming, the weather in Central Florida is friggin cold and rainy. When it warms up a bit I will crawl under the GMC with the camera and see what I can do. Whenever I'm at Jim Bounds shop I look at coaches that are on the lift to see if anyone else has a filler pipe like mine. Haven't seen one yet. Jim says he hasn't seen one like this either. If I remember correctly it's a cast piece, probably made from aluminum or something like that -- it's not like, for example, a steel pipe that was bent in an exhaust pipe bending machine. I should have taken pictures of it a couple years ago when I was re-doing all the fuel hoses. At the time I thought all GMC's were like this, now I know.
Bob Heller
2017 Winnebago 29VE
Winter Springs FL
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| Re: Reversing main and Aux tank [message #73720 is a reply to message #73705] |
Sat, 13 February 2010 12:28 |
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Matt Colie
Messages: 8547
Registered: March 2007
Location: S.E. Michigan
Karma: 7
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Senior Member |
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| bobby5832708 wrote on Sat, 13 February 2010 09:49 |
What I did was swap the 2 fuel lines coming from the tanks at the selector valve and then, to make the gauge read the proper tank, swap the 2 gauge sender wires on the dashboard switch. That's it. Total time was probably under 1/2 hour.
Mike, I will try to get a picture of the filler pipe in the next few days. Due to global warming, the weather in Central Florida is friggin cold and rainy. When it warms up a bit I will crawl under the GMC with the camera and see what I can do. Whenever I'm at Jim Bounds shop I look at coaches that are on the lift to see if anyone else has a filler pipe like mine. Haven't seen one yet. Jim says he hasn't seen one like this either. If I remember correctly it's a cast piece, probably made from aluminum or something like that -- it's not like, for example, a steel pipe that was bent in an exhaust pipe bending machine. I should have taken pictures of it a couple years ago when I was re-doing all the fuel hoses. At the time I thought all GMC's were like this, now I know.
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Bob,
This sounds like a really interesting mod, but I have a question.
Where does the fill pipe go up to??
Mine is not that far under the floor above right now.
Matt
Matt & Mary Colie - Chaumière -'73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan with OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Near DTW - Twixt A2 and Detroit
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| Re: [GMCnet] Reversing main and Aux tank [message #73759 is a reply to message #73715] |
Sat, 13 February 2010 21:02 |
Kosier
Messages: 834
Registered: February 2008
Karma: 1
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Senior Member |
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----- Original Message -----
From: "Emery Stora" <emerystora@mac.com>
To: <gmclist@temp.gmcnet.org>
Sent: Saturday, February 13, 2010 12:48 PM
Subject: Re: [GMCnet] Reversing main and Aux tank
>
> On Feb 13, 2010, at 2:35 AM, Ken Burton wrote:
>
>>
>>
>> I would rather just put a check valve in there. I do not know
>> what
>> diameter you would need but they make 1.25" brass ones for
>> sump pumps.
>> --
>> Ken Burton - N9KB
>> 76 Palm Beach
>> Hebron, Indiana
> I
> I have doubts that the normal plumbing check valve would work
> very
> well there. There isn't much head pressure to keep the valve
> closed
> due to the short height of the fuel tanks. There also would be
> a lot
> of vibrating or sloshing back and forth in a vehicle going down
> the
> road versus the static placement of a check valve in a house
> plumbing
> application. The normal plumbing check valve has a flapper
> that is
> held against either a polished brass seat or a polymer seat
> such as
> Viton. It requires some up stream pressure to seal it.
>
> Emery Stora
Emery,
A swing check would normally be unacceptable in this application,
as
it's normally a downhill run. But, in this case, I think it
would be fine.
Inertia would close it under braking and gravity would close it
while
going down hills. If they're a good American-made valve, they
will
seal if they close. I've used them for vacuum breaks on low
pressure
steam boilers and they never leak. JWID
Gary Kosier
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| Re: Reversing main and Aux tank [message #73774 is a reply to message #73616] |
Sat, 13 February 2010 23:01 |
Luvn737s
Messages: 1106
Registered: June 2007
Karma: 2
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Senior Member |
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As an aside (in otherwords, WARNING Thread Creep) if the fuel gauge moves after switching between main and aux tank, is that a certain indication that the valve has opened to allow aux fuel to flow, or is the indication independent of valve position?
Randy
1973 26' Painted Desert
Ahwatukee (Phoenix) AZ
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| Re: Reversing main and Aux tank [message #73779 is a reply to message #73616] |
Sun, 14 February 2010 01:01 |
Adrien G.
Messages: 474
Registered: May 2008
Location: Burns Flat, OK 73624
Karma: 1
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Senior Member |
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Bruce,
When I rebuilt the frame, I made the front tank the main tank, by swapping the hoses and sending wires location on the selector valve. That's the simplest way to do it.
I also did the upside down "U" trap. I cut a pocket on the underfloor insulation to get a little more height for the trap.
I was able to have the bottom of the trap even with the top of the tanks. I used 1¼" copper tube and fittings, hoses and clamps to connect.
Not sure how it works. Redoing the inside now, so I haven't been out with it get.
After I was done, with the frame, I thought that I should have spent a little more time and move the 2 fuel tanks forward, and that would make room for a gray water tank where the main tank would be.
Oh well. Next time.
Adrien & Jenny Genesoto
75 Glenbrook (26-3) Mods LS3.70 FD / Reaction Sys / 80mm Front&Intermidiate / Hydroboost / 16" Tires / Frame Rebuild / Interior Rebuild
Yuba City,Ca. Text 530-nine-3-three-3-nine-nine-6
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