I'm going to put an aux fuel tank in my 2005 Duramax and have a question. I've been told that this can play games with the computer and send the truck into limp mode. Something about the tank needs to register empty once in a while. The install kit I plan on using is from Northern Tool and sounds like it siphons fuel into the oem tank when it gets down to a certain level. Experts,what say ye?

I think your information has gotten mixed up. The "problem" you are hearing about is nothing that will send the truck into limp mode. What happens is that when you have driven for a considerable distance (about 150 miles in one shot) the computer believes there is something wrong with fuel gauge as it has not moved off full. When this happens it immediatley goes to empty and the little yellow light comes on. It will stay "empty" until the sensor starts to move again. This usually happens once the aux tank is dry. It's not that big of a deal so long as you are aware of what's going to happen in advance. If this is a concern you could always leave the valve closed on the aux tank until the stock is empty (or any point you choose) and then turn the valve on...I just leave my valve open on the aux all the time. It is one of the best mods you can do IMO. When hauling my 5er it is priceless.
BTW, I used the same Northern Tool kit you have...it's not a siphon...it gravity feeds into your OEM tank as you use fuel so your fuel gauge will always read full until the aux is empty, then it will work as normal.

The only issue I had when I gravity fed my tank is that when both tanks were full and I parked the truck for a 1/2 day or so, it would spill a little fuel from the filler cap on the OEM tank.

I have since set mine up with a pump and a shutdown safety valve that is operated from the cab. The only problem with my current system is; instead of spilling a little fuel, if you leave the pump on beyond OEM tank full, you can put all the fuel on the ground. I know a guy who put 12 or so gallons out going down the road. Talk about ruining your mpg. :D

The only issue I had when I gravity fed my tank is that when both tanks were full and I parked the truck for a 1/2 day or so, it would spill a little fuel from the filler cap on the OEM tank.

I have since set mine up with a pump and a shutdown safety valve that is operated from the cab. The only problem with my current system is; instead of spilling a little fuel, if you leave the pump on beyond OEM tank full, you can put all the fuel on the ground. I know a guy who put 12 or so gallons out going down the road. Talk about ruining your mpg. :D

Did you get the kit from northern tool for the gravity feed system? Mine has a float type valve in the "T" that shuts the gravity feed off when the oem tank is full. Mine leaked initially but that turned out to be a small pin hole in the weld of the "T". Since I fixed that, mine has never leaked even in the scenario that you describe...

I've not had any problems with mine. I used the 3/4(?)" vent tube instead of the kit. It's just an easier/less expensive installation. I strongly recommend replacing the OE fuel cap with a locking cap. This prevents a potential leak below the aux fuel tank.

I put a timer switch on my pump as The auxilary tank is 65 gallons. Now if I forget to turn it off it takes care of itself. The timer goes from 0 to 30 minutes. No more spills.

i have a transfer flow 50 gal,never had a problem with gauge or any thing else,

The only issue I had when I gravity fed my tank is that when both tanks were full and I parked the truck for a 1/2 day or so, it would spill a little fuel from the filler cap on the OEM tank.

I have since set mine up with a pump and a shutdown safety valve that is operated from the cab. The only problem with my current system is; instead of spilling a little fuel, if you leave the pump on beyond OEM tank full, you can put all the fuel on the ground. I know a guy who put 12 or so gallons out going down the road. Talk about ruining your mpg. :D


Try an in-line shut off valve or ball type valve in the feed line. Only open it when you need it. That should take care of the leak.

what type of timer did you use and where did you purchase it? :)

I purchased the timer at a hardware store. It was for 110 application but it works well on 12 volts too. I placed it under the dash on the right side so I can reach it easily. It came in a metal box,but I removed it and so it would fit under the dash. You can make it go just minutes or the full 30. They also have one that can run up to an hour,but 30 minutes works well for me. Ialso have an electric shut off valve in line so there can be no draining when the pump is off.

I borrowed a friends truck, 06 Dmax that had the aux tank, and he did not tell me about the truck going to empty thing, and I was driving to TX. When that gauge went to empty, I shut the truck off and coasted to the side of the road and called him back. He told me not to worry, it is the computer not getting a indication of movementr from the fuel gauge, and when the aux get empty and the level actually moves the float, the gauge will work again telling me I have no fuel in the aux. Gravity feed aux tank.

Anyway it was a learning expirience for me to the aux tanks, now when I can justify one, I will get one.

I just looked at northerntool.com and I see alot of tanks but no plumbing kit. Can anyone reference me to a kit that I could use to adapt a current aux tank?

Try this http://www.northerntool.com/webapp/wcs/stores/servlet/NTEProdinfo?productId=200315503&prnbr=3490902&storeId=6970&catalogId=4006970&langId=-1