Installation questions/issues with truck auxiliary fuel tank

Just bought an F 250, 6.7 diesel and am in the process of adding an aux fuel tank. I purchased, but have not rcvd yet, a RDS 60 gallon gravity fed for the bed along with the accompanying installation kit ( hose, check valve, worm clamps, etc). The RDS model no is # 72771 from Northern Tool

While trying to clear up the idea of where to add the in feed check valve on the filler tube, I had a conversation with a tech guy at Northern who inadvertently informed me that if the truck had a vented tank ( which the 250 does) that the gravity feed would have to be turned on/off manually to fill the truck tank, or the fuel would leak on to the ground from the vents in the tank. I confirmed that the truck tank is vented today with the service dept at the Ford dealer where I bought the truck and they agreed with the tech guy from Northern about the possible overflowing onto the ground.

Now interestingly enough, a gentleman, a street away from me, with a 250, diesel, who pulls a 5th wheel,  also installed the same tank with the same connector kit and told me that he leaves his aux tank valve open all the time when on the road. He specifically told me that the fuel gauge in the 250 will read full until the aux tank is empty and the 250 starts to use fuel in the truck tank. That's when the fuel gauge will start to move. So I know I'm not imagining this.

Now, obviously someone's story is not right here and I suspect it's the guy on the next street. Not sure tho ! But more importantly, if it really means that the valve must stay off until I manually have to fill the truck tank, I have no problem with that, but if that's the case,  I'd like to make sure I put that valve on the front of the aux tank(facing the rear of the truck bed), rather than in between the tank and the front wall of the bed, where it would be real difficult to open/close on a frequent basis.

Anyone have any experience with the gravity feed tanks and vented tanks ? And what is your experience with this issue ?

Thanks in advance for your input.

Ed

I bought a tank and electric fuel pump for mine, so I can't help you with your question.....but.....just remember...a 60 gallon tank full of diesel fuel will be in the range of 560 to 570 lbs.....and that weight will count against your cargo carrying capacity of the truck. 

diesel fuel.....7.5 to 7.7 lbs/gal.  = 462 lbs
Tank that you bought.... 91 lbs
Vairous hoses/valve/clamps = ???
Total = @560 lbs

I ran an aux tank in my 1999 F-250 7.3 for years and here's what "I" would do after spending a lot of time working out the kinks on my last one.

Gravity feed is nice but may or may not work the way you'd like to think.  An inexpensive solenoid pump (low pressure 2.5psi - 4.5psi or thereabouts) wired to a switch in the dash will serve you well.  You'll need to watch that you don't over fill your main tank but I used to simply use time to gauge it and it worked well.  I also wired in an electric shut off valve with the fuel pump so that one switch operated both.  Keep in mind that you will be making stops for leg stretches regardless of whether or not you need fuel so this is a good time to transfer some fuel.  Also most modern fuel gauges don't reset quickly while the engine is running so just because your putting down the super slab happily transferring fuel and the gauge only reads 2/3rds doesn't mean you aren't pumping precious dinosaur ancestors out onto the interstate.  Another thing to keep in mind is that your aux tank will probably sit with ULSD (the diesel equivalent of ethanol in my opinion) for long periods of time.  ULSD likes to absorb water and the little critters that live in diesel fuel multiply faster with water so a simple fuel filter adapter (I recommend a large screw on for a big truck) will save your engine fuel filter from having to deal with any contaminates which will eventually grow in your tank.  If you're having to run bio diesel then this is a MUST!!

I liked the idea of an aux tank and if I still had a pickup (switched to a Freightliner with 90 gallon tanks) I'd do it again.  Having the ability to "shop" for fuel going down the road is nice although saving enough to offset the aux tank and accessories purchase will probably take you longer than you'll own the truck.

Regarding the price aspect, in the previous post ^^^^^^^^, it may not take as long as you think.  Last weekend I made a trip of approx 600 miles.  Diesel fuel is at $2.15/gal where I live and I left the house with approx. 68 gallons of fuel.  Diesel prices along the Interstate ranged from $2.55 to $2.69 gallon.  My truck, when towing my toy hauler gets approx 9 mpg, so that's 66 to 67 gallons of fuel.  Multiply that 66 gallons of fuel times the .40? to 50? a gallon difference ( say 45? average), and you've got $30 difference in one trip.  I make approx 10 trips like this a year, so there's $300 in the first year of ownership.  I've got approx $550 invested in my tank, pump, and fuel filter, so less than two years of use and it's paid for itself.  AND...I buy regular diesel fuel in town as opposed to having to buy Biodiesel at the truck stops.

I have no experience with Fords but I have installed slip tanks in 4 Duramax's from 2005 to 2011. I gravity fed all of them into the vent line from the normal fill point and have never experienced any issues with overflowing. I have a shut of valve at the tank and run with it open. 

I have that tank in my F-350 and like your neighbor have had no problem leaving the tank open. Like he says the fuel gauge doesn't move until the auxiliary tank is empty. The check valve works fine as long as it is installed as directed. My vent is though a small tube that leads all the way up next to the fill cap.

I guess I'm confused as to "why" you wouldn't get an overflow if you were feeding constantly into the main tank via gravity with no shutoff valve.  To me the physics of it says that when the main gets full the gravity feed would force fuel out of the vent/overflow port, what am I missing?