Fuel Tank Interesting Plumbing...

J

jjdebarros

Member
Oct 22, 2015
42
11
8
Spokane, WA
Hi,

I've had a fuel problem since I bought my '77 Royale where I have a slow leak/drip when filling the tanks FULL.

Since discovering this, I've only been filling the tanks somewhere between 1/2 and 3/4 full with no leaks.

I've dropped the tanks to try and locate the problem, and replace the fuel lines.

In doing so, I discovered a routing / plumbing that looks 'unique'...

Any reason to maintain this, or should I redo it back to 'normal'?

The first item is the backflow valve that is between the front and back tank.

The second item is the plumbing for the Onan (which is a 6500 Commercial GenSet).
The back tank is plugged on where the Onan should draw from.

And the rear fuel line has a 'T' going to the Onan. Where it looks like I could drain my tanks dry.

Should I remove the backflow and replace with a piece of rubber tubing and replumb the Onan to the tank tap?

Thanks!

--
'77 Side Bath Royale
Spokane, WA
 
Coachman didn't use the generator dip tube. So yes it can leave draw both tanks pretty dang low!

I changed over to the dip tube on my Royale when I redid the tanks

No idea what a backflow valve is, does it prevent fuel from going from the back tank to the front tank?

________________________________
From: Gmclist on behalf of JJ DeBarros
Sent: Tuesday, March 7, 2017 3:08:45 PM
To: gmclist
Subject: [GMCnet] Fuel Tank Interesting Plumbing...

Hi,

I've had a fuel problem since I bought my '77 Royale where I have a slow leak/drip when filling the tanks FULL.

Since discovering this, I've only been filling the tanks somewhere between 1/2 and 3/4 full with no leaks.

I've dropped the tanks to try and locate the problem, and replace the fuel lines.

In doing so, I discovered a routing / plumbing that looks 'unique'...

Any reason to maintain this, or should I redo it back to 'normal'?

The first item is the backflow valve that is between the front and back tank.

The second item is the plumbing for the Onan (which is a 6500 Commercial GenSet).
The back tank is plugged on where the Onan should draw from.

And the rear fuel line has a 'T' going to the Onan. Where it looks like I could drain my tanks dry.

Should I remove the backflow and replace with a piece of rubber tubing and replumb the Onan to the tank tap?

Thanks!

--
'77 Side Bath Royale
Spokane, WA

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Replumb the capped line to the onan. My 77 Royale was the same way and I replumbed it last summer, that will prevent (by design) the onan running you
completely out of gas. If I recall the onan shuts down and you have may be 5-6 gallons left in the rear tank.

The backflow its interesting. I suppose if its not broke dont fix it. The only purpose I can think of and it was on purpose since the fill tube was
cut out, was to force fill the rear tank to capacity, then the front. Many on the board are smarter than I but I think if that tank was absolutely
full and the fuel expanded a bit, it would start leaking out the vents.. where as if the fill tube had room to breathe back up to the front tank and
eventually the filler neck it would help to vent a bit.




--
77 Royale, Rear Dry Bath. 403, 3.55 Final Drive, Lenzi goodies, Patterson carb and dizzy.
Mid Michigan
 
Seems to me the backflow valve would be more likely to fill the front (Aux)
tank first since it would inevitably have a little forward pressure drop.
Wayne may be right about the possible venting problem, but I doubt it would
become a problem.

Whomever installed that valve must have done a lot of "uphilling" &
"downhilling", resulting the movement of fuel some have described here.
Otherwise, why bother? And why bother removing it if that's not where the
leak is, which seems unlikely since it only occurs with full tanks.

Regarding your leak: Did you replace the seals on the removable "plugs" on
which the plumbing and level senders are mounted? Maybe that's where the
leak is? Another possibility is the seal around the terminal for the level
sender -- they're mostly in pretty bad shape by now.

Ken H.

> Replumb the capped line to the onan. My 77 Royale was the same way and I
> replumbed it last summer, that will prevent (by design) the onan running you
> completely out of gas. If I recall the onan shuts down and you have may
> be 5-6 gallons left in the rear tank.
>
> The backflow its interesting. I suppose if its not broke dont fix it.
> The only purpose I can think of and it was on purpose since the fill tube
> was
> cut out, was to force fill the rear tank to capacity, then the front.
> Many on the board are smarter than I but I think if that tank was absolutely
> full and the fuel expanded a bit, it would start leaking out the vents..
> where as if the fill tube had room to breathe back up to the front tank and
> eventually the filler neck it would help to vent a bit.
>
>
>
>
> --
> 77 Royale, Rear Dry Bath. 403, 3.55 Final Drive, Lenzi goodies, Patterson
> carb and dizzy.
> Mid Michigan
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
 
I'd put it back to stock. I can postulate a situation where you'd just as soon the backflow preventer could cause a problem. As to the Onan feed, a
lot of Transmode upfitters did the feed that way to save about an hour of labor. Which makes me wonder about the caliber of their upfits in the areas
you can't see. Including my Norris upfit which was plumbed the same way. And still is.

--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
 
The back flow, your alluding to the tank selector switch. You need to
replace it as it has the old type rubber that is deteriorating and the
ethanal is attacking it.
The Coachman has the generator fuel pulling from the main line. I prefer it
that way as I tend to run on low fuel level.

> Hi,
>
> I've had a fuel problem since I bought my '77 Royale where I have a slow
> leak/drip when filling the tanks FULL.
>
> Since discovering this, I've only been filling the tanks somewhere between
> 1/2 and 3/4 full with no leaks.
>
> I've dropped the tanks to try and locate the problem, and replace the fuel
> lines.
>
> In doing so, I discovered a routing / plumbing that looks 'unique'...
>
> Any reason to maintain this, or should I redo it back to 'normal'?
>
> The first item is the backflow valve that is between the front and back
> tank.
>
>
> The second item is the plumbing for the Onan (which is a 6500 Commercial
> GenSet).
> The back tank is plugged on where the Onan should draw from.
>
>
>
> And the rear fuel line has a 'T' going to the Onan. Where it looks like I
> could drain my tanks dry.
>
>
>
> Should I remove the backflow and replace with a piece of rubber tubing and
> replumb the Onan to the tank tap?
>
> Thanks!
>
> --
> '77 Side Bath Royale
> Spokane, WA
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>

--
Jim Kanomata
Applied/GMC, Fremont,CA
jimk
http://www.appliedgmc.com
1-800-752-7502
 
I think I understand the reason for the check valve and it is a rather novel idea to keep the rear tank fairly stable.
It would probably help keep you from uncovering the fuel pick up as the fuel tries to run to the forward tank on a long down hill run. Maybe a little
overkill but I don't really see a down sides to it other than an additional piece of rubber in the system.
Checks are usually quite robust and a failure shouldn't do anything more than not perform their intended purpose of stopping the reverse flow. Anyway,
JMHO
Hal
--
1977 Royale 101348,

1977 Royale 101586, Diesel powered,

1974 Eagle Bus 45',w/slideout
 
I thought about the fuel transfer issues going up hill and down hill, but that backflow valve is in the filler pipe if Im looking at the photos
correctly. There is a separate rubber hose 1 1/2 inch or so diameter which connects the tanks for transfer purposes like going up and down hills.

If anyone put a backflow vale in that smaller section of transfer hose it could be very very bad if the front tank was empty and you went down a steep
long hill. you would stall out and the backflow would prevent fuel from hitting the front tank. Regardless of what position the fuel selector was
placed.
--
77 Royale, Rear Dry Bath. 403, 3.55 Final Drive, Lenzi goodies, Patterson carb and dizzy.
Mid Michigan
 
I still would like to put a real valve in the fill line between the tanks. That check valve in the picture will only stop the main tank from dumping
into the auxiliary tank when you try to stop on a down hill. If I could find the valve I want (a 1.5" iris valve that I have seen in aircraft) then I
could do some amazing inventory management. As is, I just have to insure that we fuel late in the driving day so as to have fuel for the APU should
we need it. It seems that switching to the auxiliary tank at the 'half gage' gets us about 60 hours and I would like to have more confidence than I
have now.

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
 
Unless you have to park nose high or low often I would remove the check. As Jim K stated, rubber plumbing parts for water are not compatible with
ethanol and I would think the rubber parts are now in bits elsewhere in the system.
--
John Lebetski
Woodstock, IL
77 Eleganza II
 
Thanks all for your comments and suggestions!

I am glad to find out that the Onan plumbing is common, but I am thinking that I will replumb to the draw tube.

As to the backflow, I am going to think about this a bit more... :?

Even if I replace it, it probably will be with a piece of rubber tubing.

Thanks again for all of the responses!
--
'77 Side Bath Royale
Spokane, WA
 
Make sure to use Gates Barrier Hose intended for use with Alcohol blended
Gasoline. It is available at auto parts stores, but probably not in the
size you need. They might have to order it for you.
Jim Hupy

> Thanks all for your comments and suggestions!
>
> I am glad to find out that the Onan plumbing is common, but I am thinking
> that I will replumb to the draw tube.
>
> As to the backflow, I am going to think about this a bit more... :?
>
> Even if I replace it, it probably will be with a piece of rubber tubing.
>
> Thanks again for all of the responses!
> --
> '77 Side Bath Royale
> Spokane, WA
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
 
> Make sure to use Gates Barrier Hose intended for use with Alcohol blended Gasoline. It is available at auto parts stores, but probably not in the
> size you need. They might have to order it for you.
> Jim Hupy
Jim K. sells everything needed. Throw some business his way:

http://www.appliedgmc.com/prod.itml/icOid/855
http://www.appliedgmc.com/prod.itml/icOid/567
http://www.appliedgmc.com/prod.itml/icOid/859
--
73 23' Sequoia 4 Sale
73 23' CanyonLands Parts Unit 4 Sale
Upper Alabama
"When I grow up I am going to be a curmudgeon."
 
That works, too. Some of the folks east of the Rocky Mountains are
concerned about shipping costs from the West Coast, I was just providing an
alternative.
Jim Hupy

> Make sure to use Gates Barrier Hose intended for use with Alcohol blended
Gasoline. It is available at auto parts stores, but probably not in the
> size you need. They might have to order it for you.
> Jim Hupy
Jim K. sells everything needed. Throw some business his way:

http://www.appliedgmc.com/prod.itml/icOid/855
http://www.appliedgmc.com/prod.itml/icOid/567
http://www.appliedgmc.com/prod.itml/icOid/859
--
73 23' Sequoia 4 Sale
73 23' CanyonLands Parts Unit 4 Sale
Upper Alabama
"When I grow up I am going to be a curmudgeon."

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> That works, too. Some of the folks east of the Rocky Mountains are concerned about shipping costs from the West Coast, I was just providing an
> alternative.
> Jim Hupy
If you need it fast and can get it locally, that might be the way to go.

Shipping isn't too bad. I got almost $400 worth of stuff due here any day and shipping was $27.94.

Since Jim added USPS flat rate shipping (if it fits, it ships) to the mix, you have more choices.

As a test, I added some stuff to my cart. Shipping by UPS ground says $23.66. USPS small is $10.80.

I always encourage people to look at the GMC vendors pricing. You gotta figure in the "right part will fit" value. Not to mention the need to keep
them in business.
--
73 23' Sequoia 4 Sale
73 23' CanyonLands Parts Unit 4 Sale
Upper Alabama
"When I grow up I am going to be a curmudgeon."
 
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