Don't Do This!

L

larry nelson

New member
Apr 9, 2001
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This is for a newer owner. Many decades ago, I discovered (with my Palm Beach), that we really don't want to switch from the Main Tank to the Aux Tank
just after you have fueled up. That coach, and my current E-II, both cough and fart and hardly can produce any power, until switching back to the Main
until more the main is emptied. Why did I switch it to the AUX, you are asking yourself......well, I reached down to switch on the fuel pump and
instead switched the fuel TANKS. I was also getting into hairy hill country and really struggling to climb even modest grades. Wondering what to do,
thinking I got a load of bad gas (remember, I had just refueled)....I was wondering if I had a serious problem in the worse possible location. My
pilot training told me to switch tanks, and then I noticed that I ALREADY HAD DONE THAT (by mistake). I switched back to the Main, and the old iron
horse smoothed out and I was on my way.

No, I never knew why both of my coaches did this. But they did and DO. Word to the wise, run your main tank down before switching. I usually go to
1/2. Just thought it might help someone smarter than me.
--
Larry Nelson Springfield, MO
Ex GMC'er, then GM Busnut
now '77 Eleganza ARS WB0JOT
 
I am believer that you can switch whenever you want. I think that keeps the fuel selector working. You don't use it for a while, your fuel
selector valve gets sticky.

when I had a carb and an electric pump on the aux side, everytime I started the coach, I switched to Aux, hear the pump run a little. fire engine
then switch to main. Usually kept it on main unless I had experience of vapor lock or thought I had potential for vapor lock.

now that I run 100% electric pumps, 2ea, 1 for each tank on my EFI system. I still switch between the two, in belief that the more you use them,
the better they are.

now what Every GMC'r should take some time and study this slide, so they understand what hills and fuel can do in the GMC:

http://bdub.net/gmcmotorhome.info/tank.html

--
Jon Roche
75 palm beach
EBL EFI, manny headers, Micro Level, rebuilt most of coach now.
St. Cloud, MN
http://lqqkatjon.blogspot.com/
 
When the tanks get a bit low it is best to switch to the main going up hill and the auxiliary going down hill because the gas will move from one tank
to the other.other then that I never had a problem.
--
Roy Keen
Minden,NV
76 X Glenbrook
 
I prefer to use the aux tank and runit down from time to time as it keeps
both tanks with rather fresh

> When the tanks get a bit low it is best to switch to the main going up
> hill and the auxiliary going down hill because the gas will move from one
> tank
> to the other.other then that I never had a problem.
> --
> Roy Keen
> Minden,NV
> 76 X Glenbrook
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
>

--
Jim Kanomata ASE
Applied/GMC, Newark,CA
jimk
http://www.gmcrvparts.com
1-800-752-7502
 
I guess every coach is different, but I've NEVER experienced any issue due to changing the tank selector valve at ANY level of fuel. I do it often
due to the having my electric pump switched with my aux tank.
--
Carl Stouffer
'75 ex Palm Beach
Tucson, AZ.
Chuck Aulgur Reaction Arm Disc Brakes, Quadrabags, 3.70 LSD final drive, Lenzi knuckles/hubs, Dodge Truck 16" X 8" front wheels, Rear American Eagles,
Solar battery charging. GMCSJ and GMCMI member
 
The original selector valve are deteriorated due to age and ethanol and
need to be replaced with newer one.

> I guess every coach is different, but I've NEVER experienced any issue due
> to changing the tank selector valve at ANY level of fuel. I do it often
> due to the having my electric pump switched with my aux tank.
> --
> Carl Stouffer
> '75 ex Palm Beach
> Tucson, AZ.
> Chuck Aulgur Reaction Arm Disc Brakes, Quadrabags, 3.70 LSD final drive,
> Lenzi knuckles/hubs, Dodge Truck 16" X 8" front wheels, Rear American
> Eagles,
> Solar battery charging. GMCSJ and GMCMI member
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
>

--
Jim Kanomata ASE
Applied/GMC, Newark,CA
jimk
http://www.gmcrvparts.com
1-800-752-7502
 
If your fuel supply system is in good condition you will have no problem switching between tanks. Two problems that I have experienced are the original tank selector solenoid valve failed with the rubber tip frozen blocking the Aux tank line. The other was the sock in the Aux tank was plugged. If you are using a one-way valve with electric fuel pumps, be sure the flow is in the correct direction. The Aux tank should function the same as the main tank as far as fuel supply, they are common above a 1/4 tank. The GMC always presents many learning opportunities.

Larry Coldren
1974 Canyon Lands
Fort Collins CO

________________________________
From: Carl Stouffer
Sent: Tuesday, September 7, 2021 06:16 PM
To: gmclist
Subject: [GMCnet] Re: Don't Do This!

I guess every coach is different, but I've NEVER experienced any issue due to changing the tank selector valve at ANY level of fuel. I do it often
due to the having my electric pump switched with my aux tank.
--
Carl Stouffer
'75 ex Palm Beach
Tucson, AZ.
Chuck Aulgur Reaction Arm Disc Brakes, Quadrabags, 3.70 LSD final drive, Lenzi knuckles/hubs, Dodge Truck 16" X 8" front wheels, Rear American Eagles,
Solar battery charging. GMCSJ and GMCMI member
_______________________________________________
GMCnet mailing list
Unsubscribe or Change List Options:
 
Take my words with a grain of salt, This has occurred with both coaches and with no known mods to the fuel plumbing. Feel free to disregard my
comments. I always assumed it was something similar to the old Bonanzas with the pressure carbs. You ALWAYS ran the main tank an hour before switching
to the aux tank as the pressure carb fed 2 gph back to the main. Since this happened to me Monday climbing the hills of AR I thought it worthy to
bring up. However it appears my two coaches are the only two that suffer from this.
--
Larry Nelson Springfield, MO
Ex GMC'er, then GM Busnut
now '77 Eleganza ARS WB0JOT
 
As I've mentioned before, the return from my EFI/Accumulator is into the
drain on the Aux tank. That has, to me, a major advantage: Unless I've
got that tank's independent pump selected, I KNOW there's fuel in it up to
the between-tanks pipe. With Aux selected, I can run the system "dry" down
to the pickup tube in the Aux, because any gas the TB doesn't accept, goes
right back to that tank.

Ken H.

On Wed, Sep 8, 2021 at 4:46 PM Larry Nelson
wrote:

> Take my words with a grain of salt, This has occurred with both coaches
> and with no known mods to the fuel plumbing. Feel free to disregard my
> comments. I always assumed it was something similar to the old Bonanzas
> with the pressure carbs. You ALWAYS ran the main tank an hour before
> switching
> to the aux tank as the pressure carb fed 2 gph back to the main. Since
> this happened to me Monday climbing the hills of AR I thought it worthy to
> bring up. However it appears my two coaches are the only two that suffer
> from this.
> --
> Larry Nelson Springfield, MO
> Ex GMC'er, then GM Busnut
> now '77 Eleganza ARS WB0JOT
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
>
 
> As I've mentioned before, the return from my EFI/Accumulator is into the drain on the Aux tank. That has, to me, a major advantage: Unless I've
> got that tank's independent pump selected, I KNOW there's fuel in it up to the between-tanks pipe. With Aux selected, I can run the system "dry"
> down to the pickup tube in the Aux, because any gas the TB doesn't accept, goes right back to that tank.
>
> Ken H.

Ken,

If by the drain for the auxiliary tank, you mean the plug in the bottom I might caution some about that. I will admit that I know my coach went to
Mexico with the prior owners, but I can see strike damage to both tanks and the transmission pan. None are huge, but they also aren't a pipe elbow
sticking down another inch plus.

I do have a suggestion. If you are working on the fuel plumbing and choose to to the High T Mod (That makes fueling go so much easier), it would be
simple to place a T in the fill vent line to the auxiliary tank and be done right there.

We use a different and so far very successful fuel management plan. We run on the main tank until the indicator says about half, then we change to
the auxiliary tank. This has two values. First, it means we are burning off the old fuel that might still be in the auxiliary tank. Second, we will
still have the bottom half that we can use some of the run the generator if we need to. So far, this has worked out well. I also have to include
that I replaced both sending units a few years back and they are both still working as hoped.

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
 
> I have return fuel going to the reserve tank through the tank drain plug. Then created a angle iron covering the fuel line to protect it from road
> debris.
>
> http://www.gmcmhphotos.com/photos/gmcmi/p68345-efi-fuel-regulator.html

What a great idea.

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
 
Matt,

Yes, I DO use the drain plug in the bottom of the Aux tank for my return
line. But that line and low-profile elbow are well protected by a thick
custom steel guard. I'm not saying it's indestructible, but if that goes,
the bottom of the tank might well have gone anyway. After 10+ years of
nationwide travel, it shows no sign of damage. :-)

Ken H.

> > I have return fuel going to the reserve tank through the tank drain
> plug. Then created a angle iron covering the fuel line to protect it from
> road
> > debris.
> >
> > http://www.gmcmhphotos.com/photos/gmcmi/p68345-efi-fuel-regulator.html
>
>
> What a great idea.
>
> 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
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
>
 
> > I have return fuel going to the reserve tank through the tank drain plug. Then created a angle iron covering the fuel line to protect it from
> > road debris.
> >
> > http://www.gmcmhphotos.com/photos/gmcmi/p68345-efi-fuel-regulator.html
>
> What a great idea.
>
> Matt

Can't take all of the credit. Got the idea from the late great Bob Drews. He also suggested to put a little bend in the tube going into the fuel tank
so the fuel squirts along the bottom of the tank to avoid a geyser effect that might aureate the fuel. Just what I learned...and now passing it
forward.
--
Larry
78 Royale w/500 Caddy
Menomonie, WI.
 
> I do have a suggestion. If you are working on the fuel plumbing and choose to to the High T Mod (That makes fueling go so much easier), it would
> be simple to place a T in the fill vent line to the auxiliary tank and be done right there.

I like that. Two birds with the one stone. Your High T vent plumbing effectively adds another "home run" vent line by separating the common.

I'm not clear on how much fuel is actually returned to the tank. Would a Y be better than a T fitting to help direct the fuel?

Richard
--
'77 Birchaven TZE...777;
'76 Palm Beach under construction;
‘76 Edgemonte waiting its turn
 
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