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Discussion Starter #1
Morning all. This weekend I completed another of my moves toward the conversion of my 1300L to expedition camper. I mounted a second 35 gallon fuel tank on the drivers side (US) directly opposite the original tank and removed the exhaust that exited in front of the rear tire and made a shorty side exit with a vertically flat muffler that comes out between the cab end and the front face of the new fuel tank.
My question is regarding the plumbing to/from the original fuel tank pump. One hose forward and one hose aft separated by the electrical cable. Which hose is the fuel pump feed and which is the return to the tank? I haven't decided whether to run a manually switched electric pump to feed the original tank when I want to or whether to run a line to the original tank vent and let the vacuum developed in the original tank as fuel is used automatically draw fuel from the new tank. My Autocar works great this way and you never have to think twice about fuel levels, just check the level in the main tank. FWIW, just to clarify, I'm not talking about a low mounted line joining the two tanks which I believe is currently illegal, but a high mounted line that takes advantage of the fact that as fuel feeds the engine, more goes out to the engine than returns to the tank and this is what creates the vacuum in the original tank that will draw fuel from the second tank when the second tank is vented to atmosphere and fuel plumbed into the vent of the original tank.
If I use a pump to transfer fuel, I will put a "T" and check valve in the return line to the main tank to keep the return fuel from the pump from ever feeding into a full aux tank. Any recommendations on a good fuel pump, diesel compatible?
 

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1980 U1000 Turbo...
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The flow direction is marked on the top of the fuel sender. Failing that, just twist the top of the sender and pull it out of the tank, it will be very obvious which is which.
 

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Discussion Starter #3
Thanks, I'll have a look. Didn't notice anything yesterday, maybe covered with enough paint to hide the markings. I couldn't find anything in either volume of my shop manuals. I suppose that I could run the truck and feel the temp of the lines too, the return from the engine should be warmer than the feed to the injection pump.
 

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ex-moglet u1700 (ex U1300L)
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My 3 tank set up. One flow, return and sender feed running at a time. Auto change over facilitated by co-pilot getting out and doing it (mostly when stationary)

:)
 

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1980 U416, 1992 U1450 DoKa
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I would use a switchable tank selector valve that has a return line and electrical connector for the fuel level sender. It costs around 55-70 USD on ebay.

Saludos
 

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Discussion Starter #6
Thanks guys, I ended putting a "T" in the return line to the main tank. I have a small electric pump on the new aux tank and have it wired into an unused switch on the dash appropriately marked. All I have to do is switch the pump on when I see the main tank getting down to about 1/4 and transfer some fuel as we keep running. When the pump from the aux tank is off, an internal check valve keeps fuel returning from the engine from entering the aux tank. Now I have 70 gallons and at least a 700 mile range, but bladders will require emptying before that's reached.
 

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U1600AG + a LR 90
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Would it not be an idea to take the breather for your main tank over to your auxiliary tank then have that tank with a breather serving both tanks, that way the breather going from the main tank to the auxiliary tank would also act as a loop should you accidentally leave the switch on to long for the fuel pump, as excess fuel would just get circulated via the main tank breather back to the auxiliary provided you have a good seal on the main tank fuel cap.

Given you may have a 1-way valve on the end of your main tank breather now which would cause pressure to build in the main tank during transfer, or if no 1-way valve fitted fuel to be pumped out via the breather once full.
 

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BenzWorld UNIMOG statesman
Unimog 404.1 Diesel (sold :( )1995 LMTV 1078
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Check your weight distribution. You might be better off to occasionaly hit your pump and balance out the tank volumes between the two.
 
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