Auxiliary fuel tank with an AUTO Fill/Stop??


Okay I did a lot of digging today. I found a couple of products I had not seen or heard of before both made by Transfer Flow.

I have sent them an email to see if I can buy the kit seperatly or not but here is what I want for my project.


And a nice write up on it from four wheeler.

I would like to have seen more on the in cab wiring as well as how they made the connections to the factory wiring. If it is all plug an play then that is a bonus but I am not against soldering into the factory harness and then heat shrinking it all when done.

I also found another product which seem to be more like what I am looking for.

Freedom Fill AUX Tank Controller.

I can't use an in bed tank as I have a canopy as well as a bed slide out which covers the entire bed, and my canopy has bins mounted in the sides which protrude into the box area. I plan to mount the fill neck for the under bed tank in the side of bed side on the drivers side directly behind the tailgate. I also can't use an extended factory replacement tank as I have an extreme duty filter unit directly in front of the facotry tank already and have plans to add a Espar heater there as well.


I built my own set-up. It shuts off the transfer pump when the aux tank is empty, but I still have to monitor the factory tank to make sure I don't overfill it.

Sean made a comment in that thread that might help you in the way you want it set up:
a simpler way is to wire a relay to the low fuel warning light (in a Toyota, this light comes on with at least one gallon left in the tank, usually more like 3), so when the light comes on, it pumps fuel from the aux. tank to the main tank. as soon as that light goes out, the aux pump shuts off. supplement this with another relay that will cut power to the aux pump if the sender of the aux tank reads "empty" and a switch to bypass this (that last bit works on aux tanks that have a float like an OEM tank)

IIRC, most low fuel warning lights work by being given a ground at the fuel tank via a simple on/off low fuel switch. You could use this to give the transfer pump relay coil a ground. You might still want to use a flow switch to prevent the transfer pump from running dry - I got my switch off ebay for just a few bucks


2010 Dodge Ram 2500 TRX4 build up

I want something that my wife can use when I go away. Currently I am sitting in Afghanistan and I would hate to have my wife use my truck and get a fine for spilling 30 gallons of fuel because she over filled the stock tank from the Aux.

If that's all you're worried about, install this:



Well I got a response back from Transfer Flow INC, but I believe that they never read my inital questions about thier tanks or systems.

"We would not supply any parts to hook up an OEM tank in the bed to another OEM tanks. We do build complete systems that would work in your bed of your truck but with our tanks only."

I have now asked if they offer a tank that goes in the location of the factory spare tire and am waiting for a response. I doubt it, but if they do I imagine it will cost much more than my intended design and be much heavier as well as metal in place of the poly tank I was planning to use.

I hate when companies are not willing to work with someone in reguards to building something different. I am not typically an off-the-shelf kind of person and like things to be done to a high standard in the way I want them which often means I have to do it myself. If I could get a wiring diagram for my truck I am sure I could produce something that could be easily used by all.

Mike S

Sponsor - AutoHomeUSA
I do not know the capacity of your Dodge factory tank, but TransferFlow makes large capacity replacement tanks for most trucks. I am planning on removing the factory tank in my F350 and replacing with a TransferFlow 43 gallon tank. This is the simple solution.

Not-so-simple solution... in my FZJ80 I have the factory tank and a Long Ranger aux tank. The truck has two parallel fuel systems that are switched from the dash tank selector switch. This system also changes the tank input to the fuel gauge. With is system there is no transfer, thus, no chance of overflow. There is a single filler neck with a cut-off for filling each tank separately.

Both of these solutions would be simple for anyone to operate without risk of spillage.


One method is to connect the Aux tank vent to the main tank vent near the fill tube. If your better half turns on the transfer pump and forgets to turn it off the excess just flows back into the aux tank.


My sending unit/pump uses 6 wires which if I was to use an aux tank with a matching pump I could wire it using a 14 pin relay and have the contacts change state from one pump sending unit to the other as long as I put a check valve on each tank. The other problem would be the fuel returning from the engine would only be routed to the main tank.

The factory tank is 30 gallons so by adding an additional 31 Gallon from a suburban fuel tank with sending unit for a 6.2 or 6.5 equipt truck I will be able to double my capacity. I looked at the titan and transfer flow OEM replacement tanks but the $1200 for 10-15 more gallons I would get I already have with the 4 (5 Gallon) fuel jerry cans in the back of my truck. I want something that will actually provide me with greater range than I have now.

I have already drawn the complete circuit for what I want to do but it all comes down to figuring out the ohm range of the sending unit I currently have in the OEM tank and how to wire in a regulator that will come on at and turn off at. Short of adding 2 liquid level switches (low and high) I am currently at a loss. I am not too bad at electronics but this has me stumped at the moment. I will figure it out but it may take me a while.


One method is to connect the Aux tank vent to the main tank vent near the fill tube. If your better half turns on the transfer pump and forgets to turn it off the excess just flows back into the aux tank.

this is a great method. I used it on my old Tacoma and it worked fantastic. If you forget (which you WILL), it just continues to recirculate until you realize the pump is still on.


rock auto is a good place to look for tank sizes. suburbans also had a 40 and 42 gallon tank that might give you even more capacity


Expedition Leader
I just use a momentary switch to transfer fuel. No way for it to accidentally get switched on or forgotten. I usually keep mine on the top half in the main tank. I transfer fuel when the main tank reads about 3/4. It only takes a few minutes to top off and be back in the top part of the main tank. I can glance at the auxiliary fuel gauge and see the amount transferred. My aux tank gauge reads in gallons.

My tank install is toward the bottom of this page: BLT Offroad Avalanche


You do want to be careful about over filling the main tank. Flooding the evaporative emission canister is a real possibility. No bueno.
Decide what range fits your travels best. For me it is the 500-600 mile range. All that extra fuel is extra weight. Don't carry more than you REALLY need. I learned that lesson with my last truck. It had three tanks. I never used the third tank. No real need to carry that extra 120# of fuel all the time. I considered a larger tank this time too. Instead I opted to use an 18 gallon tank over the larger 39 gallon. Better ground clearance and less weight.
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I am planning to use a 31 gallon poly tank for a 81 suburban originally equipt with a 6.2L diesel so that the float is weighted correctly. This tank measures almost the same as the stock spare tire (28"x28"x13") and uses a 0-90 ohm sending unit. I also plan (carter 12v) to mount my pump directly a water seperator fleetguard filter unit.

I am going to call and see how much I can get the Freedom Fill Kit

I could easily wire the pump to a push button momentary button but I would want to add a time delay off relay so that the pump will run for a set time (5mins) and shut off so that I don't have to hold the button on to use. I would put the button in a spot not likely to be bumped and install a cover with guard on the switch. I have completely wired vehicles with EFI, nitrous, and dual ignition and more from scratch so I know I can wire a simple tank sending unit and pump. I just wish I could find a wiring diagram for the factory fuel system in my truck.

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