I have bought an auxiliary fuel tank for my truck and I am going to hook it up to where it gravity feeds into the trucks main tank. Now my question is, what will this to my overhead computer? will it mess up all the readings? Will it throw any codes since it will take a long time for the main tank to finally read a fuel level? Thanks in advance

 

If I leave mine open it will throw a code once it is filled and the drain valve is still open, so I usually let it fill the OEM tank at the end of the day or when it is way down since it takes quite awhile to fill. The code goes away after a bit if the valve is shut. The overhead will read OK except for distance to empty which will change until no more fuel is draining into tank.

 

Yeap, the overhead computer will go nuts trying to figure out were the fuel came from.

Lets say I have 35 gallons in the aux tank. Thats 1/2 tank. I fill the trucks tank. Total on board 70 gallons. The fuel guage in my truck reads both tanks as one as a percentage of the entire capacity of 105 gallons. The Trax II indicates gallons in the trucks tank, aux tank and shows total of both.

When I burn down to about 3/4 tank in the truck, the aux tank will start adding to the main tank 3-5 gallons at a time. What ever the overhead says
for miles left to empty at that time stays there. Estimated mileage shown in the overhead also hangs.

The only way I can figure fuel mileage is to unplug the pump on the aux tank and use the main tank only. I'm looking for a small flow meter that I can install in the line to count gallons transfered during any period. Knowing that willl allow me to leave the pump on and figure mileage by hand premised on the amount it took to fill up the trucks tank plus what was transfered. The Trax II is a good tool. It can be off by 3 or more gallons.

My truck has a range of 2000 miles running lite and about 1200 miles towing.

Dave