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Hi Eric, I really appreciate having someone knowledgeable to ask this one. I love everything about my 2001 C3500 except the towing range. I'd like to add a smaller transfer tank (30 to 40 gallons) and wondered about the feasibility of feeding directly into the filler neck with a low pressure fuel pump, something in the 3 to 9 psi range and 30 to 45 gph feed. The vent tube comes up to about an inch or so from the neck and seems to be capped off. Is this a cap, or a pressure relief valve (doesn't look like one), and would I be letting myself in for trouble if I fed directly into this tube. Thanks loads, Jim.
 

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Well, I can share my experience if it helps. I installed a 50gal Transferflow in-bed tank, and fast fillneck kit. The hose to which you are referring (correct me if I'm wrong Eric) actually does not go to the tank, but routes to the rear diff. It appears to be a vent hose of some sort, that runs from the top of the diff, along the frame, over the gas tank and attatches to the fillneck. At least mine does. I originally thought the same as you, then I followed it and noticed it did not connect to the tank but runs over it. Odd placement for it. The fillnecks on our trucks have an internal vent as seen here..



This is the OEM fillneck, with the outer rubber hose removed, revealing the plastic overflow tube. It's sort of like a tube within a tube. This makes tapping into it, as I can see with my limited fabricating skills, not easy. With my fillneck kit, I replaced the above with a hose that not only had a large opening, but an external vent hose which you then tap into with a double tee. One tee connects to feed hose, one tee connects to a hose that serves as a return for overflow, so my Aux tank can take back what the main cant hold if there is a malfunction. As far as using a pump that delivers at 30-45gph, IIRC my pump delivers at 1/2 gal per min, so that sounds about right.


Also, if you do choose to tackle this, its an easy opportunity to add extra filtration. I simply put a Racor 2mic filter in-line from the Aux tank. Keep in mind though that you have be sure the flow rate for your filter jives with what the pump is capable of sending. Hope this helps.



Mike
 

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I have installed a 40 gal tank that I made myself. (take a look at my www.)


I made a alum. Tee that went in my fuel fill line. I kept the inside plastic thingy intact. I only use a simple single acting fuel valve that I activate from in the cab. I watch my level on both tanks and when need more fuel in the main tank, I cut on the switch (Tenneessee talk
) for a fill up going down the road. It is just gravity feed so it is not real fast. I kept my stock tank cap, and if I forget to cut of the valve it has never overflowed the main tank cap vent spring. If you have a pump it probably would over come the spring in the cap and you could have a spill!
 

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Thanks, Mike, I'd figured out that that wasn't the vent tube but I was stuck on a feasible way to tap into the stock fillneck. Do you have to drop your tank to install the TransferFlow fillneck? This sure seemed like an easier project when I started thinking about it
.
 

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I did not drop my tank to install the fillneck, it was a very tough fit without a hoist. I ended up wedged between the frame and box to get a reach to the clamp, and then it was painfully slow 1/8 turns to loosen it. I loosened the band clamps that hold the tank, but that just lowered it a little bit, and it's actually easier to get the the OEM fillneck clamp if the tank is all the way up since you have to reach over the framerail.


Cmadmaxman I considered doing the same, but researched it and found out a gravity feed is illegal, violation of Title 49 Code of Federal Regulations, Part 571, Standard 301, which could pinch the offender to the tune of $2500 in civil fines if busted. Figured I'd just get a pre-fab system. How would one get busted you might ask. Well, if you got in an accident..... there was a fuel leak....truck gets towed...you get the picture
.





Mike
 

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I had heard the same thing but thought that was with out a valve to cut it off! I know that there is a company that makes saddle tanks that flow into the main tank without any valves! The problem with that setup was it kept the main tank full for too long so the fuel gauge would act funny. Also not safe I think. On that system you would change out the cap on your main tank for one with out a breather, then the saddle tanks would have the vent.


I could no see any diffrence with my set up to say a transferflow system because if the lines get severed in an accident, there would be the same problem that I would have. Fuel leaking from severed lines.


The electric valve that I have in-line shuts off when the key is off so no fuel to leak!


I would like to look at the Fed. Reg. you talked about. Got a link?


Thanks, don't want to get into trouble.
 

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Here is the general page that lets you search for regulations.


http://www.access.gpo.gov/nara/cfr/index.html


You can follow the links to get to Title 49, Chapter 5 NHTSA/DOT, which will take you to Part 571 Standard 301. Reading the standard, it would appear not to directly implicate gravity feed systems, however, as is with all federal regulations they are interpereted to apply to a given application. These regs apply to passenger vehicles and trucks under 10k. There are some gravity feed systems which can be used on certain vehicle types (ICC Diesel systems for example). The purpose of this and most engineering regulations is to spell out a standard which vehicles must meet. Any modifications must at a minimum meet OEM standards. The regulations dictate in this case, fuel system designs, which is why OEM tanks do not feed from the bottom, for example. Ever wonder why sending units are in the top of a tank and are required to draw up out of a tank? Regulations make it so, because any fuel system breach should not allow the contents of a tank to drain. It would be easier to have sending units at the bottom of a tank, however that would be a failure point subject to the forces of gravity. Manufacturers design the fuel systems to retain the fuel in the tank in most situations, barring an actual puncture of the tank itself. Cutting the suppy line of my Aux tank, or breaking off any component up to the tank will only drain the fuel in the line itself, since the sending unit is on the top, and draws fuel out. I'm sure with your system, which you say has a valve at the tank, would not leak out any more fuel than in the line either, however, if the valve failed, it could discharge the entire contents of the tank due to its gravity feed design. It is this design difference, which per se makes a gravity feed system unable to meet at a minimum OEM standards, which makes it illegal. Now that is, exactly, what is referred to as legal mumbo jumbo. But thats how it works. Not to mention the other design requirements which must be met, such as a rollover valve, etc, that aftermarket manufacturers have already designed into their systems. But Federal Motor Vehicle Safety Standards aren't the only regulations you have to worry about, theres also VESC-22, NFPA 1192, ANSI 119.2, EPA, and State regulations which would also come into play, as States all impose regulations that mirror Federal laws.
Laws which were put in place to avoid having millions of 75 Ford Pinto clones on the road that burst into flames after every fenderbender. But, with my senseless rant almost finished, it really doesn't mean much in your case, because unless you become overcome with waves of unbearable guilt and drive your shiny DMAX over to the nearest State Police Post and turn yourself in, no one will be the wiser. If your still wondering where your setup fits into the big picture, you can email the appropriate agency and get a clarification. Anyways, thats my rant and I'm stickin to it!






Mike
 

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Thanks Mike for the great info.



I see what you are saying. Point well taken and sounds like we all need to stick to it. Will be makin some changes sounds like!


Made all the openings on the top of tank to take care of that. Just need to finish it up!
 

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I have my 41 gal tank from Northern Equipt which is made by a company in Florida plumbed into the OEM fuel system using a 6 port valve. I control it by a switch on the dash. I get the quantity of both tanks on the gage and am using one tank at a time. The return fuel goes back to the tank it came out of. I had to cut the OEM fuel lines in front of the cooler to install the valve. The tank has a rollover valve to prevent fuel spills incase of an accident. I really like the setup and it meets the DOT regulations. There is no danger of overfill of the OEM tank so I don't have to watch it real close. I use the aux tank first and then switch to the OEM. That way if there is ever a problem I have fuel in OEM to go to.



Tom
 
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