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Thread: Momentums with Dual Fuel Tanks
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10-01-2020, 10:40 AM #1
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Momentums with Dual Fuel Tanks
With the Dual Fuel tanks, there's one for the generator and one for the toys, right? Is there a way to transfer fuel from one to the other?
I think there are 2 fills, so obviously you can pump from the 'Toy' tank to the 'Genny' tank fill, but is there any way to empty the 'Genny' tank short of running the generator?
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10-01-2020, 10:49 AM #2
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You are correct that the generator tank can be filled from the pump tank. I strongly recommend only using ethanol-free fuel.
The only thing I can think of to empty the generator tank other than running the generator, would be to siphon the fuel from it. You might also be able to use a manual fluid transfer pump.2016 Grand Design Momentum 385TH
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10-16-2020, 06:59 PM #3
I am going to do a mod on this to make it possible to move fuel from the gen tank to the toy tank
I will use a electric fuel pump and a motorized ball valve
I am going to cut the 1/4” suction line on the gen tank and install a tee going to the ball valve then to the electric pump then to a tee installed in the suction line of the toy tank
Then wire it up with a couple of switches install in the fueling compartment
About a $100 in parts and an afternoon should do it
The end result will be the ability to transfer fuel from the gen tank to the toy tank by flipping a couple of switchesLast edited by huntindog; 10-16-2020 at 07:03 PM.
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01-03-2021, 09:31 PM #4
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Did you get this implemented? I want to do the same thing, so I took a look under my 349M to see what was there. I think I can make what I need with a couple of fittings and a 3 way valve. Here's my plan ..
This is the fuel pump showing the line coming from the "toy" tank, which is the rear tank. It looks like 3/8" or 1/2" fuel line - pretty simple.
I'm thinking I can splice a 3 way valve in this line with one side going to the toy tank & the other going to the generator tank.
The line going to the toy tank is just the existing one. For the generator tank, I would replace the elbow fitting on the tank (shown below) with a "T" - one side going to the generator, the other going to the 3 way valve. This is presuming the generator fuel pump will stop any suction created in the line. If not, I guess I could put in a one way valve.
Thoughts?signature
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01-04-2021, 04:52 AM #5
Yes I did it. There was no issue with the generator line. Evidently, the fuel pump prevents reverse suction... That was good. I plumbed it a little different using the motorized ball valve. I installed a 3 position rocker switch in the control panel for it.(it conrols both thr pump and the valve It looks factory. I used a electric fuel pump rated @35 GPH to transfer the fuel. So it will take 20 minutes or so for a complete transfer. You solution will for sure be cheaper, and simpler, with no need to transfer the fuel. Where are you thinking of mounting the valve?
Make sure that this valve is compatible with gas, on at least some of them the seals are not.
2021 398M Full Body Paint 8k axles. LRH tires. Disc brakes.
Two bathrooms, no waiting 155 fresh, 104 black, 104 grey 1860 watts solar.
800AH BattleBorn Batteries No campgrounds 100% boondocking
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01-04-2021, 05:37 AM #6
Thinking some more about your solution.. You would likely be fueling the toys thru the 1/4" line. That would be pretty slow. Also, it may be a problem for the pump trying to suck that hard thru a 1/4" line... It may be OK, IDK... I bet that pump is pretty expensive though.
The line to the pump is marked as 1/2". It is a small 1/2" though.
on edit: I say likely as replacing the fitting on top of the tank MAY allow for a larger line, IF the suction line inside the tank is larger, or can be replaced with larger... IDK as I just teed into my 1/4" rubber line.Last edited by huntindog; 01-04-2021 at 05:43 AM.
2021 398M Full Body Paint 8k axles. LRH tires. Disc brakes.
Two bathrooms, no waiting 155 fresh, 104 black, 104 grey 1860 watts solar.
800AH BattleBorn Batteries No campgrounds 100% boondocking
2020 Silverado High Country 3500 dually crewcab Duramax Allison
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01-04-2021, 07:43 AM #7
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Good to hear you got it going! I'd love to see a photo of your setup if you can post one.
I'm thinking on the same bracket as the pump itself or maybe make a separate bracket that bolts on using the pump mounting bolts. I'm not keen on drilling more holes in my new RV. For what I'm doing, I probably won't use it very often - maybe just for pulling fuel out of the generator tank at the end of the season.
Absolutely! The valve I'm looking at is made for transferring fuel on boats.
https://www.westmarine.com/buy/west-...male--13854765
Good point and you're right - those pumps are typically expensive. I have one on my old toy hauler and it's about $300. I think they usually use a plastic gear mechanism internally (instead of a rubber diaphragm like on a carbureted car) so they're somewhat less susceptible to suction damage. The 3 way valve I found is 3/8" but I'll keep looking to see if I can find a larger one.
As for putting a "T" on the generator tank, I'm hoping Grand Design used the same sized fuel line and hardware in both tanks.
I may not get to this before summer. I have both a new truck & new RV so I have a ton of projects lined up to get them ready for this coming season. Being able to transfer fuel is lower on the priority list than about 4-5 of them.signature
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01-04-2021, 11:11 AM #8
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I'm going to tackle this project this spring, when it warms up. I hate the fact that the gasoline in the generator tank has to sit all winter with no easy way of getting it out. I always add StaBil to the tank at the end of the season, but my plans will allow me to turn 2 three way valves and be able to draw from the generator tank, using the existing pump for the other tank. At least this way, I can pour Stabil in the generator tank, then switch the valving and start the pump and just recirculate the gas back into the generator tank.....which should mix up the gasoline and Stabil completely.
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03-28-2021, 09:18 AM #9
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I took a different route and had an additional bung welded on the tank when I dropped it to have a return bung welded on for an EFI generator. I installed an Onan Commercial mobile 7000 EFI which requires a return fuel line. I just installed a an electric 3 way valve to choose which tank the factory pump sucks from.
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03-28-2021, 09:48 AM #102021 398M Full Body Paint 8k axles. LRH tires. Disc brakes.
Two bathrooms, no waiting 155 fresh, 104 black, 104 grey 1860 watts solar.
800AH BattleBorn Batteries No campgrounds 100% boondocking
2020 Silverado High Country 3500 dually crewcab Duramax Allison
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