Auxiliary fuel tank

[Dallas47]

I have a auxiliary gravity fill to main tank fuel tank in my 2015 f350 super duty. I pulled out with trailer after filling both main an aux. an about 5 miles I got a reduced power an check engine light. Pulled over an took fuel cap off an diesel ran out apparently the check valve failed that allows fuel in but not over fill. Shut valve off an after fuel was no longer running out power was restored an check engine light went out after shutting off an waiting a few seconds. Continued on trip with valve shut with no problem. Anyone had similar experience.

[Big Piner]

I can only relate to similar experience with the fuel, not the truck. I do not think it is the fuel check valve from the aux tank causing your check engine light nor do I think anything wrong with your check valve. The check valve senses when the fuel tank and lines are full. If you remove the truck fuel cap then yes fuel will come out as the valve is releasing fuel from the aux tank and the fuel will flow to the least resistance (out the truck fuel fill). The directions on my tank said to fill the main truck tank first, then fill the aux tank. On one occasion I accidentally left the cap of the truck fill off after filling the truck tank and proceeded to fill the aux tank (leaving the shut off valve open) and fuel began to come out the truck fill. Lesson learned. I leave my shut off valve in the open position at all times, the check valve is working as there is no fuel leaking out, I only fill up when fuel in main is less than half tank. With all the sensors on the newer trucks it might have sensed a problem with the fill cap, as it fixed itself after you removed the cap and reinstalled it.

[mhs4771]

The only issue I have with my '18 Chevy is that the computer doesn't sense any fuel being used by the main tank, so after approx 100 miles it generates a code and causes the dash fuel guage to drop to empty. I have a Scan Guage, so when we stop for a potty break I just clear the code and fuel guage goes back to full.

[geobet]

My previous truck, Ram 2500, had similar problems with the aux tank plumbed into the main tank. My current truck 2018 Ram dually, has a 40 gal or so aux tank. I didn't want a repeat of previous problems so I plumbed in a 12 v fuel pump going into a water block filter and a 5 micro filter. I've got it set up so that when stopping for a potty break, I simply insert the fuel nozzle into the main tank and pull the handle. Fills the main tank, as well as offering additional filtering, really fast.

[Bad Moon]

I would NEVER use gravity fill, for exactly the reason you noted. I use a 17 gallon auxiliary tank in my tool box, that draws from the top, with a Holley clone electric fuel pump that plumbs into the main fuel tank relief vent , using a clear fuel filter and a check valve. Switch with indicator light in the cab, to a relay that takes power from the camper harness. I wait until i am down to 1/4 tank left, and hit the switch while on the road. Never had a CEL, and it is fun to watch my "DTE" indicator increase, and my fuel gauge go toward "F". Shopping on ebay I have less than $200 invested. And the fuel pump makes enough noise that there is no danger of leaving it running when I stop the truck. One note: Diesel is pumped out of the ground at about 50*F and expands quite a bit, so a full auxiliary tank on a hot day will spew out fuel, so I vent through a cheap radiator recovery tank, that sucks the fuel back into the tank when it cools off at night.