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Old 07-28-2016, 12:14 AM   #1
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How does an auxiliary tank typically work?

Does the dash just read full until the aux tank is empty or do you need to do something to transfer fuel?

I know with gas systems you don't want to overfill the tank because of the vapor recovery system, is that an issue with diesel and is it a problem with an Auxiliary tank?

When you fill up, do you have to fill both tanks or does the transfer keep up with the pump?
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Old 07-28-2016, 07:43 AM   #2
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I believe most folks just use the aux tank as a carry or transfer tank. Some dieharders will plumb it in but most will use a pump and transfer fuel from the aux tank into the fuel tank.
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Old 07-28-2016, 08:04 AM   #3
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You can find all different kinds of ways to transfer fuel from the aux to the main tank. We went with the Transfer Flow 50gal in bed tank with Trax 3. The fuel is transferred a little at a time keeping both tanks at the same approximate level. No need to worry about remembering to shut off fuel or take time to transfer.
So far, diesel fuel systems don't have the vapor recovery systems and are just vented like the old gasoline tanks.
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Old 07-28-2016, 08:37 AM   #4
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There is more than one system available.

With a diesel engine, you can use a gravity flow system. The simplest uses a valve in a fuel line between the bottom of the auxiliary tank and the filler tube of the stock tank. The fuel flows from the auxiliary tank into the stock fuel tank and keeps the stock tank full as long as there is any fuel in the auxiliary tank. So the fuel gauge on the truck always reads full until the auxiliary tank is empty.
RDS Diesel Install Kit for Auxiliary Diesel Fuel Tank — Northern Tool + Equipment

Transfer Flow uses a bit different methodology, and they have a TRAX display that shows the remaining fuel in both tanks. But they cost a lot more than the simple gravity flow systems.
Transfer Flow, Inc. - Aftermarket Fuel Tank Systems

For gasoline, gravity flow is illegal, so you must use a pump of some sort to pump the gas from the auxiliary tank to either the engine or the stock gas tank. Transfer Flow is the King of those systems, but others are available for less money.

An "auxiliary" tank transfers fuel or gas automagically from the auxiliary tank to the truck, or by turning a manual valve. But a more common method is a refuel tank. A refuel tank uses a pump that you must turn on and off, or a manual pump for which you must use elbow grease to pump fuel from one tank to another - to transfer fuel to the stock fuel tank or to the fuel tank on another vehicle.
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Old 07-28-2016, 01:42 PM   #5
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Quote:
Originally Posted by SmokeyWren View Post
There is more than one system available.

With a diesel engine, you can use a gravity flow system. The simplest uses a valve in a fuel line between the bottom of the auxiliary tank and the filler tube of the stock tank. The fuel flows from the auxiliary tank into the stock fuel tank and keeps the stock tank full as long as there is any fuel in the auxiliary tank. So the fuel gauge on the truck always reads full until the auxiliary tank is empty.
RDS Diesel Install Kit for Auxiliary Diesel Fuel Tank Northern Tool + Equipment

Transfer Flow uses a bit different methodology, and they have a TRAX display that shows the remaining fuel in both tanks. But they cost a lot more than the simple gravity flow systems.
Transfer Flow, Inc. - Aftermarket Fuel Tank Systems

For gasoline, gravity flow is illegal, so you must use a pump of some sort to pump the gas from the auxiliary tank to either the engine or the stock gas tank. Transfer Flow is the King of those systems, but others are available for less money.

An "auxiliary" tank transfers fuel or gas automagically from the auxiliary tank to the truck, or by turning a manual valve. But a more common method is a refuel tank. A refuel tank uses a pump that you must turn on and off, or a manual pump for which you must use elbow grease to pump fuel from one tank to another - to transfer fuel to the stock fuel tank or to the fuel tank on another vehicle.
Yep, what he said. I have had gravity flow on 3 different diesel trucks, fill both tanks to the max if you want, turn manual switch to start feed, when the aux tank is empty your truck dash fuel gauge will start to go show fuel usage. I never turn the switch off at the aux tank when traveling and using a lot of fuel,never had a problem, it ain't rocket science.
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Old 07-28-2016, 02:11 PM   #6
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porchdog2 has the same setup I have--I leave the shutoff valve on the tank open all the time. Fill truck only, fill truck and aux tank, whichever way you want to do it. Have used the same tank for over 250k miles on 3 trucks. I can usually get 650-700 miles towing heavy and 1100 miles when solo without needing to refuel. Really can save $$ when looking to put 70+ gal in at a time.
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Old 07-28-2016, 04:47 PM   #7
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Originally Posted by eipo View Post
I believe most folks just use the aux tank as a carry or transfer tank. Some dieharders will plumb it in but most will use a pump and transfer fuel from the aux tank into the fuel tank.
Nitpicking, but in that case it's not called an auxiliary tank but a refuel tank or a transfer fuel tank. As a general rule, refuel tanks are less expensive than the same size auxiliary tank because the refuel tank doesn't have a threaded bung in the bottom of the tank where the gravity feed fuel line is connected.
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Old 07-30-2016, 08:40 AM   #8
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Thanks for the info. The Trax3 system looks cool but I really don't like how it operates. I'd rather it keep the truck tank full the way a gravity feed works. While it would be nice to see the level of the aux tank, It's not like you're a bad way if the aux tank runs dry. You'd still have most of the truck's tank available.
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Old 08-03-2016, 03:55 PM   #9
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I talked to the techs at Earl Owens in Carrolton Tx and was told that Ford went to a sealed system and you can no longer use a gravity flow. I had wondered why I could not find it for a 15 or 16 Ford. Dodge & Chevy units are still available from RDS I think.


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Old 08-03-2016, 04:46 PM   #10
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I have a 90 gallon Weatherguard and a 40 gallon main tank. Towing, that gives me roughly 1,200 miles before I HAVE to fill up. The transfer tank has a 15 GPM pump on it. I manage filling the transfer tank by resetting the trip meter when I fill the transfer tank.
It's not a big deal to me to stop every 300 miles or so and fill up the main tank. Plus I don't have to worry about did shut off the gravity feed or not. Push comes to shove, I can siphon from the transfer to the main if my pump dies. Haven't had to do that yet.

Just my $0.02
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Old 08-03-2016, 05:02 PM   #11
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Love my 91 gallon RDS fuel tank/toolbox combo. Gravity feeds into main tank. Gives me over 1000 miles between fill-ups. Best thing is I never have to drag my trailer to the gas station. I unhook, set up camp, and then go get fuel while DW fixes dinner.
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Old 08-04-2016, 12:37 PM   #12
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I just installed a 60G RDS tank a few months ago. They are designed to be used as a gravity tank that transfers fuel into the main tank. I chose to to plumb a diesel filter and diesel pump between the RDS and main tank. My concern was the gravity valve failing and me dumping fuel all over the interstate. I ran a switch up to my dash and turn it on when I get down to 3/4 tank. Downfall is that I don't know how much fuel is in aux tank. I monitor it by watching my FUEL USED gauge.
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Old 08-05-2016, 01:46 AM   #13
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Quote:
Originally Posted by Duoglide1 View Post
I talked to the techs at Earl Owens in Carrolton Tx and was told that Ford went to a sealed system and you can no longer use a gravity flow. I had wondered why I could not find it for a 15 or 16 Ford. Dodge & Chevy units are still available from RDS I think.
I would imagine you could still do it by putting a T in the line from the tank to the fuel pump but don't quote me on that.

Quote:
Plus I don't have to worry about did shut off the gravity feed or not.
What would be the problem of leaving the valve open?
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Old 08-05-2016, 07:13 AM   #14
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What would be the problem of leaving the valve open?


Worse case, a fuel spill.
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