Home » Public Forums » GMCnet » One tank full, one tank empty!
| One tank full, one tank empty! [message #78307] |
Sun, 28 March 2010 15:47  |
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RF_Burns
Messages: 2277
Registered: June 2008
Location: S. Ontario, Canada
Karma: 3
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Yesterday I had The Murray out for a short run. After about 8 miles the engine lost power, sputtering and died.
D'OHH! due to the new fuel selector I now have a separate switch from the OEM to flip tanks. So I was showing full on the unselected tank when the selected tank was empty. I just finish making up a relay so the OEM switch can do the job again.
So once that was discovered I flipped the switch and off I went to the gas station to fill up. It only took 80 litres (20US gals) to fill it. So my gauge reading full on one tank and empty on the other seems right, but why? There was only one small hill, maybe 25ft high rising and falling in about 1 mile so hardly enough to throw the fuel from one tank to another, besides I was running on the Aux tank which should fill up more in hills. Otherwise the road was fairly level.
I had all the tanks down last summer while the engine was out for a rebuild. All the hoses were replaced at that point, including the filler hoses.
I do have EFI and the return line is in the filler line, but I would expect the Aux tank being the front one would again get more return fuel than the rear (main) tank.
Any ideas?
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: One tank full, one tank empty! [message #78367 is a reply to message #78307] |
Sun, 28 March 2010 20:57  |
Larry C
Messages: 1168
Registered: July 2004
Location: NE Illinois by the Illino...
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I had all the tanks down last summer while the engine was out for a rebuild. All the hoses were replaced at that point, including the filler hoses.
______________________________________________________________
I have had the tanks down and hoses replaced.
My understanding and they way I looked at the reinstall is the gas is free to flow back and forth to the front and rear tank, they should more or less always act as one tank. The reserve is just a little space in one of the tanks.
it sounds like your tanks have been connected differently or you have a kink or a plug in the large hose somewhere.
The selctor valve should have no bearing over which tank remains full and which tank will empty first as both tanks are connected with the large filler hose and act as one tank, more or less.
The reserve is only about 6 or 7 gallons, all the rest is used as the normal supply. the reserve has a baffle that will refill when the tank is filled, don't forget to put the reserve swith back to normal.
LarC ( Had to replace the hoses since they had cracked, Well worth the replacement effort )
Gatsbys' CRUISER  08-18-04
74 GLACIER X, 260/455-APC-4 Bagg'r
Remflex Manifold gaskets
CampGrounds needed, Add yours to "PLACES" />
http://www.gmceast.com/travel
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| Re: [GMCnet] One tank full, one tank empty! [message #78369 is a reply to message #78367] |
Sun, 28 March 2010 21:05 |
emerystora
Messages: 4442
Registered: January 2004
Karma: 13
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Senior Member |
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On Mar 28, 2010, at 7:57 PM, Larry wrote:
>
>
> I had all the tanks down last summer while the engine was out for a
> rebuild. All the hoses were replaced at that point, including the
> filler hoses.
> ______________________________________________________________
>
> I have had the tanks down and hoses replaced.
>
> My understanding and they way I looked at the reinstall is the gas
> is free to flow back and forth to the front and rear tank, they
> should more or less always act as one tank. The reserve is just a
> little space in one of the tanks.
>
> it sounds like your tanks have been connected differently or you
> have a kink or a plug in the large hose somewhere.
>
> The selctor valve should have no bearing over which tank remains
> full and which tank will empty first as both tanks are connected
> with the large filler hose and act as one tank, more or less.
>
> The reserve is only about 6 or 7 gallons, all the rest is used as
> the normal supply. the reserve has a baffle that will refill when
> the tank is filled, don't forget to put the reserve swith back to
> normal.
>
> LarC ( Had to replace the hoses since they had cracked, Well worth
> the replacement effort )
>
>
> --
> Gatsbys' CRUISER :d
> 74 GLACIER X, 260
That's not quite the way they work. The filler tube is mounted to the
side of the tanks about 1/2 way up. So, if the motorhome were to be
operated always on the level then each tank would be drawn down
together until they were both left with about 12 gallons in each.
Then the tank which is selected by the selector valve would empty,
leaving 12 gallons in the other.
What messes this up is when the GMC is driven up and down hills. When
that happens some of the fuel can flow from one tank to the other as
the GMC tilts going up or down a hill. When that happens it is then
about impossible to accurately know how much is in either tank.
I really don't think there is a baffle that keeps a reserve. As far
as I know there is no baffle in either tank.
There is a good writeup with diagrams on Gene Fisher's site that
explains it all.
http://gmcmotorhome.info/tank.html
Emery Stora
77 Kingsley
Santa Fe, NM
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| Re: One tank full, one tank empty! [message #78377 is a reply to message #78307] |
Sun, 28 March 2010 22:02 |
rvanwin
Messages: 325
Registered: April 2007
Location: Battlefield, MO
Karma: 6
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Senior Member |
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| RF_Burns wrote on Sun, 28 March 2010 15:47 |
I do have EFI and the return line is in the filler line, but I would expect the Aux tank being the front one would again get more return fuel than the rear (main) tank.
Any ideas?
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Bruce,
I can't explain why one tank would read completely full while other is empty, but mine does come close. My EFI return in also in the filler tube. When full, both tank levels lower the same until just below 1/2 tank. At that point, it seems that all the fuel is pumped from the main and returns to the aux. tank. When the main tank low fuel light comes on, I switch to the aux. and I will usually have between 1/2 to 3/4 on the gauge. The strange part, is now, if I continue to use the aux tank it will go until the low fuel light comes on then I will have a little less than 1/2 in the main (time to look for a station). Seems it always returns to the tank not being used which seems strange. Although the pump does pump a lot of volume so I guess it pumps it out of the tank being used faster than it returns into that tank making it seem that only the other tank if filling?
Maybe now that you have full tanks, you can monitor the behavior as you use up the fuel.
Randy & Margie
'77 Eleganza II '403'
Battlefield, MO
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| Re: [GMCnet] One tank full, one tank empty! [message #78385 is a reply to message #78369] |
Sun, 28 March 2010 22:52 |
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I've seldom been able to put in as much as 25 gallons when the gauge shows
just less than 1/4 full. It has been that way since I purchased the coach in
2007. I've not dropped the tanks but I suspected that there's some type of
blockage going to one of the tanks.
When I am putting in fuel and it gets near the neck (listening to the change
in sound while filling) it will really burp bigtime and then gurgle a good
bit. Someone told me it shouldn't exhibit that type of behavior. I tend to
agree. But, until I drop the tanks, I'll never know.
I would think, based on how the system works, that when I get to 1/4 full it
should take more than 25 gallons to fill up. To my way of thinking, 25
gallons shouldn't register as full but it does.
In the meantime, I just stop every 2.5 hours, stretch, and get another 22
gallons of fuel.
By the way, on my trip to/from Montgomery the coach averaged 8.54 mpg over
the 1100 miles of traveling. Gas was cheapest in Louisiana.
Byron Songer
1978 Royale by Coachmen
Louisville, KY
Personal - http://web.me.com/bnsonger
Eastern States - http://www.gmceast.com
Emery Stora wrote:
>
> That's not quite the way they work. The filler tube is mounted to the
> side of the tanks about 1/2 way up. So, if the motorhome were to be
> operated always on the level then each tank would be drawn down
> together until they were both left with about 12 gallons in each.
> Then the tank which is selected by the selector valve would empty,
> leaving 12 gallons in the other.
>
> What messes this up is when the GMC is driven up and down hills. When
> that happens some of the fuel can flow from one tank to the other as
> the GMC tilts going up or down a hill. When that happens it is then
> about impossible to accurately know how much is in either tank.
>
> I really don't think there is a baffle that keeps a reserve. As far
> as I know there is no baffle in either tank.
>
> There is a good writeup with diagrams on Gene Fisher's site that
> explains it all.
>
> http://gmcmotorhome.info/tank.html
>
> Emery Stora
> 77 Kingsley
> Santa Fe, NM
>
>
> _______________________________________________
> 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:
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--
Byron Songer
Full-timing to enjoy the USA
Former owner but still an admirer
GMC paint schemes at -
http://www.songerconsulting.net
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| Re: [GMCnet] One tank full, one tank empty! [message #78388 is a reply to message #78385] |
Mon, 29 March 2010 01:37 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Senior Member |
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| Byron Songer wrote on Sun, 28 March 2010 22:52 |
I've seldom been able to put in as much as 25 gallons when the gauge shows
just less than 1/4 full. It has been that way since I purchased the coach in
2007. I've not dropped the tanks but I suspected that there's some type of
blockage going to one of the tanks.
When I am putting in fuel and it gets near the neck (listening to the change
in sound while filling) it will really burp bigtime and then gurgle a good
bit. Someone told me it shouldn't exhibit that type of behavior. I tend to
agree. But, until I drop the tanks, I'll never know.
I would think, based on how the system works, that when I get to 1/4 full it
should take more than 25 gallons to fill up. To my way of thinking, 25
gallons shouldn't register as full but it does.
In the meantime, I just stop every 2.5 hours, stretch, and get another 22
gallons of fuel.
By the way, on my trip to/from Montgomery the coach averaged 8.54 mpg over
the 1100 miles of traveling. Gas was cheapest in Louisiana.
Byron Songer
1978 Royale by Coachmen
Louisville, KY
Personal - http://web.me.com/bnsonger
Eastern States - http://www.gmceast.com
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Byron,
What is the possibility that the fuel gauge is off? Have you ever run your coach until it needs to go on the reserve tank or until the low fuel light comes and then fill it up to see how much it takes?
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: [GMCnet] One tank full, one tank empty! [message #78401 is a reply to message #78388] |
Mon, 29 March 2010 07:20 |
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No, never done that. Too afraid it's off the other way and the copilot would
rip me a new one. I did get close, once. Got cold feet and stopped for gas.
Byron
Ken Burton wrote:
> Byron,
>
> What is the possibility that the fuel gauge is off? Have you ever run your
> coach until it needs to go on the reserve tank or until the low fuel light
> comes and then fill it up to see how much it takes?
> --
> Ken Burton - N9KB
> 76 Palm Beach
> Hebron, Indiana
_______________________________________________
GMCnet mailing list
List Information and Subscription Options:
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--
Byron Songer
Full-timing to enjoy the USA
Former owner but still an admirer
GMC paint schemes at -
http://www.songerconsulting.net
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| Re: [GMCnet] One tank full, one tank empty! [message #78408 is a reply to message #78385] |
Mon, 29 March 2010 08:43 |
Larry C
Messages: 1168
Registered: July 2004
Location: NE Illinois by the Illino...
Karma: 0
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Senior Member |
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In the meantime, I just stop every 2.5 hours, stretch, and get another 22
gallons of fuel.
_____________________________________________________________
Byron
I can say positively that the fuel guage is only a not very accurate "WARNING" of your fuel amount.
The tanks are large and very thin so the guage is victim of sloshing gas and depending on where the float is set can give a variety of gas readings which may not be close to actual.
2.5 hours only gives yo about 150 miles travel, that computes about correct with the 300 mile limit most of us might give it before filling.
If you are worried, carry a 5 gal tank and give her a 250 mile run, then see what you take when you fill. If you are truely running on only one tank, you will know it and then need to find why the other tank is not supplying fuel.
My guage was fairly accurate until the tanks were dropped and re-installed. It is hap-hazzardly working now but since I never trusted it anyway, it is merely a warning.
I bought a bicycle cyclometer which computes MPH, trip time, Trip miles, etc.... I use the Trip miles for fuel refuel as it can count down from 300 miles and be reset each fill. The sensor is not that bad to install and has worked flawlessly.
2.5 hours is just too many times to stop for gas on a long trip, however, as Emery said, the hills and mountains moves gas around so I would fill before ascending or descending any grades.
Good luck
LarC ( Look at the gas guage as more of a decoration than an actual fuel indicator )
Gatsbys' CRUISER 08-18-04
74 GLACIER X, 260/455-APC-4 Bagg'r
Remflex Manifold gaskets
CampGrounds needed, Add yours to "PLACES" />
http://www.gmceast.com/travel
_
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| Re: [GMCnet] One tank full, one tank empty! [message #78409 is a reply to message #78369] |
Mon, 29 March 2010 08:51 |
Larry C
Messages: 1168
Registered: July 2004
Location: NE Illinois by the Illino...
Karma: 0
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Senior Member |
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I really don't think there is a baffle that keeps a reserve. As far
as I know there is no baffle in either tank.
__________________________________________________________
Thanks Emory
I would swear I read that a baffle was installed for the reserve cap but what you have explained makes more "Money Sense".
It is sort of the same but using the tank as a baffle rather then actually installing one.
But it still does not explain why he has a full tank and an empty tank, maybe a bad sender????
Could he be running on the reserve and the valve wont switch to normal????????????
LarC ( Its more fun to find the fix then to live with the problem )
Gatsbys' CRUISER 08-18-04
74 GLACIER X, 260/455-APC-4 Bagg'r
Remflex Manifold gaskets
CampGrounds needed, Add yours to "PLACES" />
http://www.gmceast.com/travel
_
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| Re: [GMCnet] One tank full, one tank empty! [message #78437 is a reply to message #78401] |
Mon, 29 March 2010 12:12 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Senior Member |
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| Byron Songer wrote on Mon, 29 March 2010 07:20 |
No, never done that. Too afraid it's off the other way and the copilot would
rip me a new one. I did get close, once. Got cold feet and stopped for gas.
Byron
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I totally understand. Pushing that thing to a gas station could be a lot of fun.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: [GMCnet] One tank full, one tank empty! [message #78464 is a reply to message #78437] |
Mon, 29 March 2010 17:48 |
shawnee
Messages: 422
Registered: February 2004
Location: NC
Karma: 0
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Senior Member |
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| Ken Burton wrote on Mon, 29 March 2010 13:12 |
| Byron Songer wrote on Mon, 29 March 2010 07:20 |
No, never done that. Too afraid it's off the other way and the copilot would
rip me a new one. I did get close, once. Got cold feet and stopped for gas.
Byron
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I totally understand. Pushing that thing to a gas station could be a lot of fun.
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Ken,
Grace does it all the time forJim K using an Olds van.
Gene Dotson
74 Canyonlands
www.bdub.net/Motorhome_Enhancements New Windows and Aluminum Radiators
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| Re: [GMCnet] One tank full, one tank empty! [message #78541 is a reply to message #78464] |
Tue, 30 March 2010 01:51 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Senior Member |
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| shawnee wrote on Mon, 29 March 2010 17:48 |
| Ken Burton wrote on Mon, 29 March 2010 13:12 |
| Byron Songer wrote on Mon, 29 March 2010 07:20 |
No, never done that. Too afraid it's off the other way and the copilot would
rip me a new one. I did get close, once. Got cold feet and stopped for gas.
Byron
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I totally understand. Pushing that thing to a gas station could be a lot of fun.
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Ken,
Grace does it all the time for Jim K using an Olds van.
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Yes, I remember Santa Rosa.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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