Fuel tank selector switch/solenoid. Really needed?

S

scott nutter1

New member
Jan 5, 2015
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Hello,
I'm getting ready to replace all my original fuel line to the ethanol resistent fuel fine.
I would like to simplify the design and go from the tanks to a coupler, single line outside the frame to a hard mount fuel filter, to a hard mount
electric fuel pump with a bypass hose(as close to the tanks as I can get), to a long run to the mechanical engine fuel pump. The fuel selector switch
would be used to turn on the electric fuel pump, if needed.
My question is, by eliminating the tank selector switch would this cause any future problems or issues? I am one of those guys who stops for fuel
every 200 to 250 miles anyways.
Thanks, Scott.
--
Scott Nutter
1978 455 Royale Center Kitchen, Quad bags.
Houston, Texas
 
You could have a problem doing this.
Because fuel can flow from one tank to the other if you allow the gas level to go below the tank fill connection (about 1/2 tank) one tank could go quite low if you are going up or down hills and then your fuel tank could suck air and your engine would die on the road.

You could get around this by installing two electric fuel pumps, one for each tank (either in-tank or external) and connecting them with a relay that would switch from one tank to the other using your dash mounted Main/Aux switch.

Emery Stora
77 Kingsley
Frederick, CO

>
> Hello,
> I'm getting ready to replace all my original fuel line to the ethanol resistent fuel fine.
> I would like to simplify the design and go from the tanks to a coupler, single line outside the frame to a hard mount fuel filter, to a hard mount
> electric fuel pump with a bypass hose(as close to the tanks as I can get), to a long run to the mechanical engine fuel pump. The fuel selector switch
> would be used to turn on the electric fuel pump, if needed.
> My question is, by eliminating the tank selector switch would this cause any future problems or issues? I am one of those guys who stops for fuel
> every 200 to 250 miles anyways.
> Thanks, Scott.
> --
> Scott Nutter
> 1978 455 Royale Center Kitchen, Quad bags.
> Houston, Texas
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
 
Emery,
If I coupled both fuel tank lines together just outside of the tanks, wouldn't I always have fuel going to either line "a" or "b" to the coupler as
long as I have some fuel in each tank? Even if I'm on a hill, one of the fuel lines should feed the main line? Or am I overlooking the obvious?
Thanks.

--
Scott Nutter
1978 455 Royale Center Kitchen, Quad bags.
Houston, Texas
 
Yes, Scott,

I learned the hard way about this issue. My beloved P.O. plumbed both together, so when smugly switching to the aux tank, I was out. What you are
missing is that if one fuel pickup is in the air, the pump will just draw that air so that there is no suction sufficient to draw the fuel back out of
the other tank. I fixed that for a few miles with a vise grip pinching off one tank feed. That's the reason behind the otherwise mysterious advice
often heard and read on the forum not to run the tanks below 1/4 full.

The dual pump solution sounds to be the best under the circumstances and it is really nice to know if a pump goes out suddenly (is there any other
way?), you have one you can switch to until you can conveniently get under the coach to replace it. Peace of mind about one thing at least. I wonder
just what the best practice is? I was going to mount a relay underneath, but am starting to be convinced by taking the trouble to run power wires to
the dash switch and doing without another relay with the attendant possible fire hazard, which I think is minimal. And if the relay's coil goes out,
you would still have 12 volts to one pump through the normally closed contacts.

Carey

--
Carey from Ennis, Texas
78 Royale, 500 Cadillac, Rance Baxter EFI.
 
Yes, one fuel line might feed the main line when on a hill but the other one might feed air. Air bubbles in the line would compress and act just like vapor lock and you won't have fuel pressure at the carb (or throttle body if you have fuel injection.)

You have to pull from only one tank to assure it working properly.

Emery Stora
77 Kingsley
Frederick, CO

>
> Emery,
> If I coupled both fuel tank lines together just outside of the tanks, wouldn't I always have fuel going to either line "a" or "b" to the coupler as
> long as I have some fuel in each tank? Even if I'm on a hill, one of the fuel lines should feed the main line? Or am I overlooking the obvious?
> Thanks.
>
> --
> Scott Nutter
> 1978 455 Royale Center Kitchen, Quad bags.
> Houston, Texas
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
 
Put the relay under the hood, not under the coach. Good wiring will rarely fail, but connections in the weather almost always break down.
--
Terry Kelpien

ASE Master Technician

73 Glacier 260

Smithfield, Va.
 
If you are going to remove the selector valve and add a second pump you are probably going to need a pair of check valves to prevent one pump from
back feeding through the other one. It seems to me like a lot of effort, and money just to eliminate a selector valve.
--
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
 
Just did fuel lines, and never understand why people are afraid of the selector valve. They are $35, and i guess i personally have yet to see a
newer one fail in the 6 years i have been around GMC's. Even if it would fail, plumbing around it is quick and pretty painless.

Here is a post of the fuel line replacement I just did. I started on saturday morning, and fuel tanks were back in, and I made a late dinner out.
Had some misc stuff to finish up on sunday morning, so the whole job was not too tough.

Here are some photos and how I did the selector valve and added an aux fuel pump. Others go the two fuel pump route, but this has worked well for
me going on 6 years now and in my humble opinion,
Much easier and simpler.

http://lqqkatjon.blogspot.com/2017/04/fuel-lines.html?m=1
--
Jon Roche
75 palm beach
St. Cloud, MN
http://lqqkatjon.blogspot.com/
 
Good points/explanitations. Thanks. I'm going to keep it stock with the selector switch intact. Maybe just run one fuel pump tied into the selector
switch "aux" position, and see how that works out. I could always install the 2nd fuel pump later if needed.
And thanks for the help..
Scott
--
Scott Nutter
1978 455 Royale Center Kitchen, Quad bags.
Houston, Texas
 
You'll like it, Scott. Best of both worlds.

bdub

> Good points/explanitations. Thanks. I'm going to keep it stock with the
> selector switch intact. Maybe just run one fuel pump tied into the selector
> switch "aux" position, and see how that works out. I could always install
> the 2nd fuel pump later if needed.
> And thanks for the help..
> Scott
> --
> Scott Nutter
> 1978 455 Royale Center Kitchen, Quad bags.
> Houston, Texas
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
 
In the interest of thread drift, why does the fuel stuff have to be on the driver's side? If the exhaust ran on the driver's side and the fuel
plumbing was all on the passenger's side, it would be better to work on stuff with your legs sticking out on the shoulder side instead of the traffic
side.
--
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."
 
Here's my solution using two Mr. Gasket pumps with built in check valves:

http://www.gmcmhphotos.com/photos/cane-9-creek-rv-park-heflin-2c-al/p58467-fuel-pump-follies.html
- several pictures.

If you do this, replace the supplied filters with the Wix replacements. The originals tend to leak at the joint where they're swaged together.

--johnny

--
76 26' Eleganza(?) with beaucoup mods and add - ons.
Braselton, Ga.
"I forgive them all, save those who hurt the dogs. They must answer to me in hell" - ol Andy, paraphrased
 
> In the interest of thread drift, why does the fuel stuff have to be on the driver's side? If the exhaust ran on the driver's side and the fuel
> plumbing was all on the passenger's side, it would be better to work on stuff with your legs sticking out on the shoulder side instead of the
> traffic side.

This is one of those design issues that you have to wonder about.
This also makes the exhaust on the curb/door side. The OE dump was in the middle, so that could not have been the driver.

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
 
There is a fuel system issue here that has been completely neglected here.

The APU/generator/genset fuel pickup is in the main tank and only reaches to the 1/4 mark (more or less).

So:
If you run out the main (rear) tank, making electricity is now not an option.
If the tanks are combined and you are below that 1/4 mark the same condition exists.

Yes, I am a little paranoid. I am old and paranoid.

You may not think this matters that much and if you are a blue roads driver that only stops in campgrounds, it might never be any problem. We don't
use the coach that way. We go places that we wanted to go because doing it as a passcar roadtrip was impractical.

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
 
I'm following with great interest as one of my next projects is to replace the fuel lines. I understand the benefit of keeping the selector valve,
but am unclear on the one vs two fuel pump(s) option...

Sincerely,
Dave
--
David del Rio - 75 Avion - Raymond, CA
 
If you use two fuel pumps (one to each tank pickup) you can eliminate the selector valve.

And, if you have two fuel pumps you have a backup just in case one goes bad.

Emery Stora
77 Kingsley
Frederick, CO

>
> I'm following with great interest as one of my next projects is to replace the fuel lines. I understand the benefit of keeping the selector valve,
> but am unclear on the one vs two fuel pump(s) option...
>
> Sincerely,
> Dave
> --
> David del Rio - 75 Avion - Raymond, CA
>
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
 
And people with two electric pumps usually eliminate the mechanical pump mounted on the engine. People with one pump usually install the single
electric pump in the rear and use it as a boost pump in case of vapor lock.
--
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
 
With two electric pumps, you can get a bayonet fitting which threads onto the carb hard line from the mechanical pump and remove and bypass the
mechanical pump. If you have keep the mechanical pump and put caps on the selector valve, you can revert to stock beside the highway in 30 minutes or
less, should both pumps fail. Never had a problem with mine, but, "belt and suspenders'.

--johnny
--
76 26' Eleganza(?) with beaucoup mods and add - ons.
Braselton, Ga.
"I forgive them all, save those who hurt the dogs. They must answer to me in hell" - ol Andy, paraphrased
 
Also hasn't some used the tank drain plugs as a place to combine the tanks ? Not sure if that's a good idea being that the coaches are so low one good
road Apple could really ruin your day.
--
Tony Cook
77' Kingsley ' SuperSession 77 '
Torrance Beach,CA
 
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