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Old 05-13-2016, 10:17 AM   #1
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Gravity flow fuel transfer tank. Need advice.

Going to buy an addition bed mounted tank. I would rather not add the electric pump to the tank since my goal is to keep everything simple and below the bed rails without the pump apparatus sticking up. It will go in a 2015 F350 DRW. I pull a 40 5th wheel and the fuel stop planning gets very difficult on long trips. I plan to go with the gravity flow type with a manual valve. Looking at a RDS 45 gal that will mount standing up in the front of the bed with my tool box flush up against it.

I only tow with this truck as it is not a daily driver.I guess I would drive on the main tank until down to a quarter tank or so and then stop and open the manual valve to start the transfer. This would allow me to run a full day and then unhook in the evening and go fuel up without the trailer. I also pull a second trailer behind the 5th wheel so you can see why I would like to be able to run all day without navigating through fuel stops pulling two trailers. That way we will only need rest area stop for our bladders.

A few questions:
1. Can you leave the valve open and transfer fuel when driving or do you have to stop and allow the transfer to take place when sitting still.
2. If driving while transferring, does it distort the fuel usage read out.
3. If it does will it reset itself when you turn the engine off and then restart it.
4. Any idea how long it takes to transfer 25 or 30 gallons?

Thanks for any advice.
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Old 05-13-2016, 12:09 PM   #2
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Assuming your F-350 has a diesel engine, RDS, the folks that make your diesel auxiliary tank, also make a gizmo that gravity flows any fuel in the auxiliary tank to the main tank without allowing the main tank to overflow. Leave it on all the time, and your main tank stays full until the auxiliary tank runs dry. After the auxiliary tank is dry, the fuel gauge works to tell you the fuel level in the main tank. Omit the manual valve, or maybe if you're a belt and suspenders sort of guy you can install both the gizmo as well as a manual valve . Sweet gizmo.
RDS Diesel Install Kit for Auxiliary Diesel Fuel Tank — Fits 1999–Current Ford, 2011–Current Chevrolet and GMC, and Dodge 1999–2012, Model# 011025 | Fuel Tank Accessories| Northern Tool + Equipment

The RDS Diesel Install Kit for Auxiliary Diesel Fuel Tank is illegal for a gasoline tank. If you have a gas engine, and you don't want to use a pump, then a manual valve and all the headaches that causes is probably the only way.
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Old 05-13-2016, 08:33 PM   #3
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Smokey is right on with his advice. The RDS system has worked very well for me in my first 350, last 450 and now my current one. Fill the truck tank, close the cap, then fill the aux tank. As you travel, the fuel will gravity feed to the truck tank as needed--the truck gauge will stay near full, until the aux tank gets low. Due to gravity feed, the flow amount decreases from the aux tank as the tank empties--I can out drive the gravity feed daily, but it catches up over night. This system can be a small problem in the '07-back models, but the '08-'10s seem to handle it just fine. Can't say to the '11s-up.
With this system, if your truck gauge lowers, you are outdriving the gravity feed, or the fuel level in the aux tank has dropped to where there isn't enough head pressure to deliver the fuel fast enough.
Your questions specifically:
1) I leave the valve open all the time when towing
2) May or may not distort the gauge reading--the truck only knows what the level in the tank is, but the computer may/may not get confused when it realizes that you have driven past the mpg/tank volume and should be empty--this was the situation with my '07, but the '09 and '10 don't notice it.
3) Truck gauge will show what is in the tank, and on mine, it climbs overnight when stopped.
4) It is basically a 'drip' system--very slow, that's why I say you can outdrive the feed if you are towing heavy and running at 60-65. You would not want to hope it will replenish while eating a hamburger, but I guarantee that you won't run out unless you don't have a bladder...
Having this extra tank was a spectacular success on our AK trip in '12 and it will be again starting this June.
Is it perfect-No. It requires holes in the bed to attach the tank and to route the feed line. If the tank were full, I don't really feel the tabs they use to attach the tank to the bed floor would hold--be sure to use fender washers on top and bottom to spread the load in a turnover. I added a fuel filter inline last year, and am amazed at the amount of sediment I get--not from the tank, from the fuel. There is also those who say the condensation in the aux tank is excessive and hurtful to the Ford system--I have not found this to be true. I drain the WIF valve every 5k miles--sometimes there is water, sometimes not, but always sediment. This sediment is NOT from the aluminum tank, but from the fuel source.
Be aware if you have a fuel system problem under warranty, and you have an aux tank in use, you are going to be fighting the Ford warranty system--just think about that.
TransferFlow is probably the cadillac of systems, very pricey, but just about as good as it gets. ATTA also has custom tanks to build to every configuration you could come up with. RDS tanks are very well built, and the gravity feed kit works very well.
I will never be without an aux tank while towing at 27+k gross--it allows me to look up prices on GasBuddy ahead of time, and also fill when camped without the trailer.
I have several times computed the overall cost of the tank install vs the $$ saved on fillups---if you use GasBuddy, and can find $0.20-0.50/gal differential in prices on the road ahead----WOW. I have over 300k miles using the RDS tank and have worked it several times to come up with===what is $0.20/gal worth over 400k miles at $3.00/gal? Most people don't drive near as much as I do, so the savings will be less or take longer to recoup the cost. Many times, I have saved +$0.40/50 gal being able to look down the road.
One caveat: do not leave the truck cap open when you fill the aux tank--the gravity feed restrictor is not a positive shutoff if the aux tank is nearing full.
Simply because I use my 450 as a daily driver and usually get 40-50k miles/year, the potential for savings just driving
If you haven't noticed--I love my aux RDS tank.
Joe
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Old 05-14-2016, 05:41 AM   #4
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Thanks for clearing up my concerns. Gota love this forum.
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Old 05-14-2016, 08:45 PM   #5
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I have a 60 gal. RDS and use a soloniod hooked to a upfitter switch. As far as your other concerns all the gauges and computer are not affected even keeps track of the gallons used. This is on the 11 to 16 trucks.
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Old 05-15-2016, 05:57 AM   #6
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Jnbhobe,

Did you install the solinoid switch to keep from having to get out and manually open and close the valve? I am okay with getting out and manually operating it but mainly concern that running with the valve open would distort the fuel read out and possibly throw a code or check engine light.

Ideally I would like to be able to fill both tanks and first run the RDS tank down and then be able to monitor the remaining fuel in the primary tank down while being able to watch the guage. I had heard that it could affect the computer since you would be logging miles with no fuel being consumed. Supposedly it would reset when the truck was turned off and then back on. This may have been on older trucks.
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Old 05-15-2016, 08:34 AM   #7
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I don't think you will have any problem with the electronics on your Ford, with the exception of some false mpg/dte readings occasionally, and things get back to normal after restarting. I have seen some really high mpg readings, but dte stays pretty close.
With a gravity feed, you still have to run the fuel thru the truck tank, so you will be taking from the aux and truck tank at the same time, until the aux runs out.
Using the aux tank will fuzzy up your calculated mpg readings somewhat also, but over a period of time, this will average out. If you are wanting to keep track of mpg and make it accurate, occasionally you will have to run on the truck tank only for a tankful, then go back and hand calculate.
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Old 05-15-2016, 10:08 AM   #8
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I had the RDS 60 gal. in my 07 Chevy 3500 and loved it. However, leaving the valve open full time, did in fact cause the trip computer to go haywire after the gauge remained on full for 40-50 mi. All of a sudden the fuel gauge would go to EMPTY. Therefore, I not only had to pull over to turn it on, I had to pull over to shut it off. I would install a solenoid valve next time. This may be a GM thing or it may have just been my 07, but it definitely was not happy staying on FULL for an extended period of time.
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Old 05-15-2016, 11:49 AM   #9
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You might get more info on a Ford diesel forum.
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Old 05-15-2016, 05:17 PM   #10
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I also have the RDS 60 gal with toolbox, and there adapter for the filler tube. I just have the manual valve and leave it open when traveling. I shut it off when I am using the truck as a daily driver with the aux tank empty. On my '03 chevy, the fuel gauge goes to empty after between 150 and 300 miles, but it will start working again when the aux tank is empty and you start drawing fuel from the main tank. I think that the '08 and up trucks the manufacturers have upgraded their computer systems so they don't get confused. I have used this for about 6 years and around 70K miles pulling the 5er, the only problem that I have had is that the check ball that lets air into the top of the tank plugged up 1 time and I had to remove it and clean it with WD40.
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Old 05-15-2016, 05:34 PM   #11
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Red face

Quote:
Originally Posted by wingnut60 View Post
Smokey is right on with his advice. The RDS system has worked very well for me in my first 350, last 450 and now my current one. Fill the truck tank, close the cap, then fill the aux tank. As you travel, the fuel will gravity feed to the truck tank as needed--the truck gauge will stay near full, until the aux tank gets low. Due to gravity feed, the flow amount decreases from the aux tank as the tank empties--I can out drive the gravity feed daily, but it catches up over night. This system can be a small problem in the '07-back models, but the '08-'10s seem to handle it just fine. Can't say to the '11s-up.
With this system, if your truck gauge lowers, you are outdriving the gravity feed, or the fuel level in the aux tank has dropped to where there isn't enough head pressure to deliver the fuel fast enough.
Your questions specifically:
1) I leave the valve open all the time when towing
2) May or may not distort the gauge reading--the truck only knows what the level in the tank is, but the computer may/may not get confused when it realizes that you have driven past the mpg/tank volume and should be empty--this was the situation with my '07, but the '09 and '10 don't notice it.
3) Truck gauge will show what is in the tank, and on mine, it climbs overnight when stopped.
4) It is basically a 'drip' system--very slow, that's why I say you can outdrive the feed if you are towing heavy and running at 60-65. You would not want to hope it will replenish while eating a hamburger, but I guarantee that you won't run out unless you don't have a bladder...
Having this extra tank was a spectacular success on our AK trip in '12 and it will be again starting this June.
Is it perfect-No. It requires holes in the bed to attach the tank and to route the feed line. If the tank were full, I don't really feel the tabs they use to attach the tank to the bed floor would hold--be sure to use fender washers on top and bottom to spread the load in a turnover. I added a fuel filter inline last year, and am amazed at the amount of sediment I get--not from the tank, from the fuel. There is also those who say the condensation in the aux tank is excessive and hurtful to the Ford system--I have not found this to be true. I drain the WIF valve every 5k miles--sometimes there is water, sometimes not, but always sediment. This sediment is NOT from the aluminum tank, but from the fuel source.
Be aware if you have a fuel system problem under warranty, and you have an aux tank in use, you are going to be fighting the Ford warranty system--just think about that.
TransferFlow is probably the cadillac of systems, very pricey, but just about as good as it gets. ATTA also has custom tanks to build to every configuration you could come up with. RDS tanks are very well built, and the gravity feed kit works very well.
I will never be without an aux tank while towing at 27+k gross--it allows me to look up prices on GasBuddy ahead of time, and also fill when camped without the trailer.
I have several times computed the overall cost of the tank install vs the $$ saved on fillups---if you use GasBuddy, and can find $0.20-0.50/gal differential in prices on the road ahead----WOW. I have over 300k miles using the RDS tank and have worked it several times to come up with===what is $0.20/gal worth over 400k miles at $3.00/gal? Most people don't drive near as much as I do, so the savings will be less or take longer to recoup the cost. Many times, I have saved +$0.40/50 gal being able to look down the road.
One caveat: do not leave the truck cap open when you fill the aux tank--the gravity feed restrictor is not a positive shutoff if the aux tank is nearing full.
Simply because I use my 450 as a daily driver and usually get 40-50k miles/year, the potential for savings just driving
If you haven't noticed--I love my aux RDS tank.
Joe
Be aware if you have a fuel system problem under warranty, and you have an aux tank in use, you are going to be fighting the Ford warranty system--just think about that.

I will address the above section of the quote.I think its funny, when i traded for my 2016 F350 dually, I had the dealership find me a aux tank/ tool box combo, cause they said they would install one at cost as part of the deal. As we were discussing the aux tank in parts, a young feller walks up and somehow gets in on the aux tank conversation. I had no idea who he was, but everyone started saying the dealership did not install transfer flow tanks and furthermore would never install such tank.i commenced to aggressively point out to the young man his assumptions on the quality of the fuel going into the system. Anyhow, one by one the deniers started to disappear, as did the young man. in the end they found a tank, shipped to the dealership, installed at the dealership, that does not install transfer flow tanks!
About two days later a small light came on, I told DW that I bet that was a ford engineer, back in parts.
I know I'm slow,but I thought it was funny.
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Old 05-16-2016, 06:28 AM   #12
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If it temporarily distorts the read out I am find with that especially since it resets after turning the key off then back on. I already know what the mileage is while pulling the 5th wheel.

I just wanted to be comfortable that the check valve with the ball check system did the job and would stop when the main tank was full without creating a spill.
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Old 05-16-2016, 07:06 AM   #13
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gregk,
I have had no trouble with the check valve in the filler neck, but you have to remember to not open the fuel cap, because then the fuel will run out.
Frank
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Old 05-16-2016, 08:53 AM   #14
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Franka548 is correct--that is why I always fill the truck tank first, close the cap and then fill the aux tank. Only took me one time to remember to CLOSE THE TRUCK TANK CAP before filling the aux tank. It's a slow drip feed, but doesn't take much diesel to make a mess...
You can't create a spill with the RDS setup unless you leave the truck cap open OR try to open it when your truck gauge still shows full. If the truck gauge is down any amount, there shouldn't be any fuel in the filler neck of the truck if you open it, and you can hear the fuel dripping out of the aux tank if you listen closely.
If you aren't comfortable thinking about this potential problem, then suggest you go the TransferFlow or the ATTA setup with pumps/switches/auto transfer capability.
Before I installed the filter in the gravity feed line, my aux tank would drain almost to empty before the truck tank began to show use; since I put the filter inline, there is enough restriction that the flow to the truck slows appreciably when the aux tank level gets past 1/2 full.
I've said this several times before on several forums--it is not difficult to save an average of 15-20c/gal if you use GasBuddy--last month, in Childress, TX, filled at the WalMart and while filling I could see the FJ sign a block south showing 41c/gal higher. Took on about 45 gallons that time--$18.45 saved that time. I drive +40k miles/year and it really pays for itself quickly with those miles. While towing, it adds up also, + the ability to fuel at times without the fiver on back.
Good luck whichever way you go--I think you will really like the extra fuel capacity even with the small hassle of filling over the bed rails--have to be careful the hose connections don't scratch the finish.
Joe
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