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Old 05-18-2017, 03:45 PM   #1
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Gravity feed or transfer tank?

I've decided to add an RDS 60 gallon fuel tank/tool box combo to my 2017 Dodge 3500 dually. I've narrowed my choices down to the gravity feed model 73326, or the transfer tank model 72744. Both have full length tool box lids, and both are 55"L, 20"W, and 22 1/2 tall. My truck is a long bed, but I want as much room and as little weight in the back as possible, so I'm sticking with a 60 gallon tank because they are only 20" wide. Larger tanks jump up to 24" or 30" wide. I don't plan to put a tonneau on the truck, so I don't mind that the tanks are taller than the bed rails. The transfer tank is about $400 more than the gravity tank, and I'm willing to eat that upfront cost.

I like the simplicity of the gravity feed tank plumbed straight into the filler neck of the truck, although I see some people complain about slow feeding, and the slight danger of a spill.

I also like the idea of having a transfer tank with 8 gpm pump, & 10' hose that I can use to refuel my truck and other vehicles as well. As I mentioned above, the transfer tank has a full length tool box lid, so the pump & hose are protected from the elements. However, a friend warned my about an increased danger of fuel contamination from the transfer tank, especially from the hose & nozzle.

I've never owned a diesel before, so I'm learning "on the fly." Am I missing something? Is there some increased danger to having a separate transfer tank that I'm not seeing?
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Old 05-18-2017, 04:15 PM   #2
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My gravity feed works perfectly. Never had a spill or slow feed.

JMHO I do not see a need for the transfer.
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Old 05-18-2017, 07:33 PM   #3
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xtasee, I guess it's just for the cool factor of being able to fuel up other vehicles in need. I'm a retired soldier and a retired Texas cop, so I still suffer from "rescuer fantasies."

If I do go with a gravity feed, it would give me the option of getting the lower profile 60 gallon tank that RDS offers (#72743). It is only 19" tall, which would leave me the option of installing a tonneau someday if I ever feel the need to. The toolbox is only 6 1/4" deep, versus 10" on the taller tank, but I can live with that.
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Old 05-18-2017, 09:26 PM   #4
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That sounds exactly like the one I bought. I did put a tri-fold over it and I also have a Pull-Rite slider hitch. Everything barely clears each other including the when the tri-fold is folded, and the shock on the hitch...

I am happy with the choice but also understand your fantasy. That could be a strong reason for the transfer option.
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Old 05-18-2017, 09:26 PM   #5
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Gravity feed or transfer tank?

Why not have both. The same transfer setup tank has all the fittings for an auxiliary tank. Plumb it in as an auxiliary tank buy the transfer hose pump and nozzle and you have both.
When you don't need the auxiliary tank shut the petcock and you have a full transfer tank.


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Old 05-18-2017, 09:35 PM   #6
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The rds 72548 is 60 gallons same size and does both and is a tool box combo as well.


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Old 05-19-2017, 02:21 PM   #7
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Just installed the Titan replacement on my Ram 3500. Not a bad install, perfect fit, not modifying or running for parts. Almost 60 gals now. Can always add the spare tire tank or in bed if needed, but 60 gals should be good. Might be something to look into, leaves my bed completely free.
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Old 05-19-2017, 05:59 PM   #8
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In order for my gang box to open with the tonneau cover on I had to block the gang box forward 10". This thread made me realize what I should do with the space I've created. They make a 40 gallon auxiliary tank that's 9-10" thick. That's my next project.
I have to stop reading these threads, I already have more to do than time allows.
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Old 05-19-2017, 10:41 PM   #9
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No thanks required, Foxfire. I'm just glad I could help you add another expensive project to your to-do list!

I decided to keep it simple, so today I had a local shop order an RDS 72743-- the gravity-feed, low-profile 60 gallon tank/toolbox. He expects to get it on Monday, and have it installed in two hours. He's charging me $1001.32, which is as cheap as I could do it myself. Tractor Supply sells the tank for $779, plus $137 shipping, and $70 for the installation kit.

Thanks for all your input, guys. Now I can focus on fixing my a/c issues.
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Old 05-20-2017, 04:08 AM   #10
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I installed a 72 gallon tank that also allows for our roll up cover and love it. Also installed the Freedom Fill automatic so when we get to 1/4 tank it fills it back up to 3/4 tank. Has a separate fuel gauge. We can now carry 109 gallons so no need to stop until we unhook. Best investment I made but the wife still doesn't agree but she isn't the one trying to find the fuel stations.

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Old 05-25-2017, 02:47 AM   #11
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I had the 60 gal gravity feed tank installed this afternoon, and it looks like they did a fairly good job of it. I could have done better, but their work looks serviceable for now. I can see some tweaks that need to be made, however.

One major problem, though. If fuel is even flowing at all, it doesn't look to be flowing fast enough to refuel me on the fly. I added 15 gallons to the aux tank four hours ago, and since then neither the truck fuel gauge nor the aux tank gauge have even moved.

I'm going to play around with it tomorrow, and make some adjustments, but I'm worried. I hope I didn't screw up by not spending $350 more for the transfer tank with the 8 cfm pump on it.
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Old 05-25-2017, 04:18 AM   #12
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Red face

Quote:
Originally Posted by Randalf View Post
One major problem, though. If fuel is even flowing at all, it doesn't look to be flowing fast enough to refuel me on the fly. I added 15 gallons to the aux tank four hours ago, and since then neither the truck fuel gauge nor the aux tank gauge have even moved.
I believe that I have the exact same tank It works perfect but check to make sure the valve at the bottom of the tank is open. Mine is tucked under the bed rail so you really have to look for it. Also you should have a vent near the filler make sure it is open and that they did not put something to block it.

Just because I worried about fuel splashing out of that vent, I put a piece of fuel hose on it and a little check valve on it that they use for axles and transfer cases . Is not necessary however. The important thing is that it will vent.

I always fill my main tank to the top, put on the cap, then fill the aux tank. I actually never shut of the valve even when I run the aux tank dry. I am sure that when traveling down the road, things move better..

Hope that helps
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Old 05-25-2017, 07:40 PM   #13
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Took the truck back to the shop this morning and after they placed a call to RDS tech support they quickly resolved the problem. When they cut into the fuel tank filler tube they installed the ball check valve on it's side, and it has to be installed vertically on top of the tube. In their defense, the installation instructions are one page long (one side) with no clear diagrams or photos, and not very well written. Tech support was right there with all the answers, though.

I put 50 gallons in the aux tank, and the main tank filled up quickly. There are no leaks or sloshing from the tank vent or from the truck tank filler. I drove over plenty of bumps and did some hard cornering too, and everything looks tight and dry.

Now I'm going to install an inline fuel filter, and while I'm at it, xtasee, I'm going to take your advise and install that length of hose & check valve on the vent. I've seen others say they only fill the tank to 50 gallons to avoid spillover from the vent, but RDS advises to fill the tank to 95%, which would be 57 gallons.
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Old 05-25-2017, 11:34 PM   #14
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Quote:
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I've seen others say they only fill the tank to 50 gallons to avoid spillover from the vent, but RDS advises to fill the tank to 95%, which would be 57 gallons.
Diesel fuel has a high coefficient of expansion in hot weather. If you fill to 95% you will surely expeerience overflow...a BIG mess. Go with what otherss have said and max at 50 gallons.
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Old 05-26-2017, 12:15 AM   #15
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My understanding is that gravity feed is illegal.

This is from the ATTA Aluminum Tank company. But you can find references to this info from the companies that make legal aux tanks.

GRAVITY FEEDING IS ILLEGAL
Here are some laws (regulations)*which pertain to gravity feed fuel tanks, and why they are illegal.

1. 49 CFR CH.III (393.65) 6d; Gravity or syphon feeding is prohibited.

2. 49 CFR CH.III (393.67) 7.4.5.; Fuel withdrawal fittings. The fittings through which fuel is withdrawn from a tank must be located above the normal level of fuel in the tank when the tank is full.
In other words, the fuel must come from the top of the tank and not from a fitting on the bottom. For safety reasons, all aluminum tanks manufactured by ATTA will have no fittings on the bottom. When in doubt, look at your factory tank.

Quote:
Originally Posted by Randalf View Post
I had the 60 gal gravity feed tank installed this afternoon, and it looks like they did a fairly good job of it. I could have done better, but their work looks serviceable for now. I can see some tweaks that need to be made, however.

One major problem, though. If fuel is even flowing at all, it doesn't look to be flowing fast enough to refuel me on the fly. I added 15 gallons to the aux tank four hours ago, and since then neither the truck fuel gauge nor the aux tank gauge have even moved.

I'm going to play around with it tomorrow, and make some adjustments, but I'm worried. I hope I didn't screw up by not spending $350 more for the transfer tank with the 8 cfm pump on it.
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Old 05-26-2017, 03:16 PM   #16
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Very informative. I am looking at adding a tank in my truck. 39 gallons in the truck fuel tank doesn't go very far! Char & Steve, thanks for the pictures!
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Old 05-27-2017, 01:05 AM   #17
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bergeman, I did some researching before I bought the RDS tank, and the consensus was that it is legal to gravity feed fuel from one tank into another, but it is illegal to gravity feed fuel directly into a carburetor or fuel injection system. RDS claims that their systems are 50 state legal, and I'm holding them to that!

I also read that companies like ATTA and Transfer Flow may be misrepresenting the truth by taking those CFR words out of context to imply that their systems, (which cost more than twice as much as gravity systems), are the only ones that are legal. It makes sense to me that using gravity to cascade diesel fuel from one tank into another is perfectly safe and legal. Using gravity to put gasoline into a carburetor? Not so much.
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Old 05-27-2017, 06:05 AM   #18
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"Using gravity to put gasoline into a carburetor? Not so much."

Interesting since a significant number of small aircraft gravity feed to the carburetor. Cessnas and Piper Cubs being a few.
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Old 05-27-2017, 02:47 PM   #19
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bergeman, I Googled 49 CFR 393.67 and it looks like ATTA forgot to mention that the regulation applies only to commercial vehicles. It also appears that ATTA chose to omit a couple of important things from the sections they so piously cited. Things like: "Except for diesel fuel tanks, the fittings must...", and "Gravity or syphon feed prohibited...directly to carburetor or injector."

§ 393.67 Liquid fuel tanks.
(a)Application of the rules in this section. The rules in this section apply to tanks containing or supplying fuel for the operation of commercial motor vehicles or for the operation of auxiliary equipment installed on, or used in connection with commercial motor vehicles.

(5)Fuel withdrawal fittings. "Except for diesel fuel tanks," the fittings through which fuel is withdrawn from a fuel tank must be located above the normal level of fuel in the tank when the tank is full.

Then I checked 49 CFR 393.65, and that reg actually reads:

(d)Gravity or syphon feed prohibited. A fuel system must not supply fuel by gravity or syphon feed directly to the carburetor or injector.
(That's where I got that from MuddFlap. I knew I had seen it somewhere!)

Nice work, ATTA, nice work!! Don't expect any business from me, you disingenuous clowns.
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Old 05-28-2017, 06:04 AM   #20
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Well that was fun. Good information to know. This topic was almost as good as the discussion on whether a non-commercial CDL is needed to pull the Redwoods.

The other rumor I heard (While researching the Aux Tank) was that non-commercial vehicles were not allowed to have aux tanks.

In the end, this all great information for the next person you looking for a tank. For me, having the extra fuel has significantly reduced my stress while driving.

Quote:
Originally Posted by Randalf View Post
bergeman, I Googled 49 CFR 393.67 and it looks like ATTA forgot to mention that the regulation applies only to commercial vehicles. It also appears that ATTA chose to omit a couple of important things from the sections they so piously cited. Things like: "Except for diesel fuel tanks, the fittings must...", and "Gravity or syphon feed prohibited...directly to carburetor or injector."

§ 393.67 Liquid fuel tanks.
(a)Application of the rules in this section. The rules in this section apply to tanks containing or supplying fuel for the operation of commercial motor vehicles or for the operation of auxiliary equipment installed on, or used in connection with commercial motor vehicles.

(5)Fuel withdrawal fittings. "Except for diesel fuel tanks," the fittings through which fuel is withdrawn from a fuel tank must be located above the normal level of fuel in the tank when the tank is full.

Then I checked 49 CFR 393.65, and that reg actually reads:

(d)Gravity or syphon feed prohibited. A fuel system must not supply fuel by gravity or syphon feed directly to the carburetor or injector.
(That's where I got that from MuddFlap. I knew I had seen it somewhere!)

Nice work, ATTA, nice work!! Don't expect any business from me, you disingenuous clowns.
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