6.7L Cummins Forum

I am building an auxillairy fuel tank that goes under my toolbox. I am trying to keep it as simple and cheap as I can. It will have gravity flow into a RDS kit on the fuel fill line, vented, etc.

Instead of a fuel guage, I am considering putting in two bungs into the side of the tank with fittings and a clear tube that I can see from the bed. The clear tube would show the level of the fuel in the tank. I would also have a fuel shut off valve in the same area.

Other than the inconvenience of not seeing the level from inside the tank, are there any do's or don'ts? Or better ideas?

i used a Chevy switch from the 70's or 80's when they had dual tanks with an electric switch in inside so i can just fill the stock tank as i drive down the road.

There are restrictions on what you can and can not do with fuel tanks. I would advise looking at the DOT / Fed regs on this. If I remember correctly, site glasses/tubes on road usage is not allowed. There are different regs for aux tanks vs transfer tanks. If you have a problem and have a spill, there are some hefty fines and liable for all clean up costs. Insurance will not cover it and you will be dropped. You do not want that to happen. Depending on your location, if you get pulled over for something and local law enforcement decide to do a walk around, you will be fined (especially in these trying times). I always look at this way, if I do a cheap job now, how expensive can it get if something goes wrong later ?

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I had a Transferflow installed in my truck, refills main tank automatically. Works like a charm.

Better check your state laws, gravity flow in some States are not OK. I have a pump and egg timer on mine, 50gal under the tool. Also you should think about a fuel filter on it, too. I have had mine on for over two years, help when on a long trip and you use the GASBUDDY.com to find cheap fuel. I jsut go off the mileage, know I can run about 550-600 miles on the back tank.