| Gas Tanks [message #320886] |
Sun, 23 July 2017 10:14  |
Ken Lit
Messages: 1
Registered: July 2017
Karma: 0
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Junior Member |
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I have a 1974 260 unit with dual 25 gallon tanks. I am confused as to how the fuel pump draws gas from both the rear main tank and the front aux tank when the dash switch is in the fuel main position. Anyone have a explanation of how this works?
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| Re: Gas Tanks [message #320891 is a reply to message #320886] |
Sun, 23 July 2017 11:18  |
mrgmc3
Messages: 210
Registered: September 2013
Location: W Washington
Karma: 2
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Senior Member |
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The tanks are separate but connected. The connection tube is at about the 6 gallon level, so you can pull 40 plus gallons from full if you leave the switch in either position. Then when you switch over you have 6 or so gallons of "reserve". As the tanks are very flat the fuel easily flows back and forth on grades.
Chris Geils - Twin Cities / W Wa
1978 26' Kingsley w/ very few mods; PD9040, aux trans cooler, one repaint in stock colors, R134a, Al rad, Alcoas, 54k mi
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| Re: Gas Tanks [message #320892 is a reply to message #320886] |
Sun, 23 July 2017 11:32 |
Tilerpep
Messages: 404
Registered: June 2013
Location: Raleigh, NC
Karma: 7
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Senior Member |
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http://www.gmcmhphotos.com/photos/data/6466/medium/GMCfueltanks.jpg
This pic may help. The two tanks slosh into each other via the filler neck until they are low.
So they slosh and both draw dawn from either pickup in either tank, until the last few gallons. So, if you fill up and leave the switch alone (either setting) and run till engine quits, IN THEORY the other tank has a few gallons. When my coach was new to me, this theory led me to waiting an hour and a half for AAA to bring me gas. Ha!
I have recently added an additional low pressure electric pump to my reserve side, but that is to address vapor lock type issues. But my selector switch now chooses which tank AND changes whether it is mechanical fuel pump or mechanical and electric fuel pump. (If this part adds to confusion, ignore, it is not OEM - but is worth checking into if you have heat related fuel delivery issues.)
1975 Glenbrook, 1978 Royale rear bath
Raleigh, NC
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| Re: Gas Tanks [message #320925 is a reply to message #320886] |
Sun, 23 July 2017 20:57 |
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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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Ken Lit wrote on Sun, 23 July 2017 11:14I have a 1974 260 unit with dual 25 gallon tanks. I am confused as to how the fuel pump draws gas from both the rear main tank and the front aux tank when the dash switch is in the fuel main position. Anyone have a explanation of how this works?
Ken,
Welcome to the group, family, cult, asylum...
How does this work?
Short answer - Very well. If you track your fuel rate (write the odo on each slip and build a spreadsheet, you will quickly find that each tank is highly variable due to the bad fills. But if you fix that (search here - recommending high T), your fuel fills can be very regular.
The cross-connection of the mid-tank fill pipe is a lot of your confusion and it is understandable.
Now, what we do is:
Run on the main until half and change over so there is no old fuel left in the auxiliary tank.
If the light comes on, go back to the main that will still have about 10 gallons in it. That is also enough for about 5 hours of APU time.
Buy fuel at 400~450 miles. Street Atlas will tell you where to start looking at GasBuddy. (Street Atlas is out of print and the nearest I have found is Furkot and that is a website application and so of limited (aka useless to most) underway.)
There is another problem, most of the tanks selector valves have gone bad because of the addition of alcohol to mototfuel to support ADM and a very few farmers. The available replacements work, but are very different.
Now Ken, you made it here and that is a real good thing. What you also may not have yet grasped is that you just collected a couple of thousand brand new old friends. Your coach is much more than a big new toy. You will soon realize that being an owner of a GMC ties you to a community like few others. This is why you need to go back to Bdub's and collect and print a copy of the Black (aka GMC Assist) list. When you need assistance, there is probably someone in striking range. These are amazing and very supportive people. For all this to work, you need to do both yourself and us a big favor. If you read down the way, you will see that we all have sigfiles. This is more than just a fad, there is a reason. That reason is so we can help each other.
To make a sigfile, go to <Control Panel/Account Settings> and scroll down. You will find the place to fill it in. This forum is a mirror of an E-mail list and even some that have high speed broad band (and indoor plumbing) still prefer to rear this as e-mail. They don't get to see the header at all. To that end, please start with a real name (so that when you meet others, they don't have to guess who you are), a short about the coach (year, version and major mods) and a geographic reference (so others will know if they can come and help).
Again, this is a community like few others. In actual fact, the only other that I know of is that of the watermen of my world. For this reason, I like to welcome new owners here much as a new owner or vessel is welcomed there. So,
May the Good Lord bless this coach and all those that set forth within her.
Welcome Ken
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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