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Fresh Water Tank Fill Issues - Momentum 397TH

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  • #46
    I have the same problem on a 395MS-R. Did you ever figure it out?
    Todd & Steph
    2022 Momentum 395MS-R
    2018 Dodge Ram 3500 Laramie Diesel

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    • #47
      bsonposh -- it would help if you tagged the individual (like I did tagged you), or quoted them, to clarify whom you're addressing so there's a notification sent to that individual. No biggie...just trying to help you get a response.
      Forum moderators are not GD employees--we are volunteers and owners presumably just like yourself. Unless specifically mentioned otherwise, we have nothing to gain should you choose to purchase a product or engage a service we discuss on this forum.

      2017 Ford F-350 DRW, '19 315RLTSPlus

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      • #48
        Thanks howson I was targeting the OP and tagging would be a good idea. mhood did you figure this out?
        Todd & Steph
        2022 Momentum 395MS-R
        2018 Dodge Ram 3500 Laramie Diesel

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        • #49
          Closely following this as we have this exact issue in our newly delivered 2023 395MS. Overflow on the aux tank always dumps first. At this point, after 4 attempts at filling fresh water, I have not ONCE been able to get the main tank overflows to drip a single drop.
          Current: 2023 Grand Design Momentum 395MS-R. FBP, dual pane windows, 3rd A/C, heat pump, Fosgate, etc.

          Truck: 2015 F350 DRW Platinum - Black.

          Previous: 2021 Grand Design Momentum 376THS-R. FBP, dual pane windows, 3rd A/C, heat pump.

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          • #50
            Assuming shaferz is using the power fill, his observations seem counter intuitive. Using power fill, water should be flowing into the main tank a lot quicker than it can flow into the auxiliary tank, assuming that the overflows are at the same elevation. If water has never flowed out of the main tank overflow, I would strongly suspect that the main tank overflow is plugged.
            John
            2018 Momentum 395M
            2018 Ram 3500 Dually
            Every day is a Saturday, but with no lawn to mow.

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            • #51
              I finally got around to flushing and filling our freshwater tanks. The auxiliary tank did overflow 1st. I checked the monitor and it only showed the main tank @ 2/3 full. I capped off the overflow on the auxiliary tank and finished filling the main tank. I have noticed previously that the tanks do balance to some extent. I can empty the auxiliary tank, go back later and it has more water in it. Not sure this helps anyone, but it seems to be a common issue.
              2022 Momentum 397THS-R 12/3/2021
              Traded 2021 Reflection 337
              2020 Chevy Silverado 3500 DRW
              Formerly M&K337

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              • #52
                MK397THR

                If the Aux overflow is left capped, what happens when water is being drawn through the pump for consumption by the trailer? Of course the main will supply the first x gallons with no issue, but when the Main's water level falls below the Aux's, will the Aux tank collapse in on itself? That's what happens to the single tank in my 315RLTS if I forget to open the overflow valve that I installed since air can't get in.
                Forum moderators are not GD employees--we are volunteers and owners presumably just like yourself. Unless specifically mentioned otherwise, we have nothing to gain should you choose to purchase a product or engage a service we discuss on this forum.

                2017 Ford F-350 DRW, '19 315RLTSPlus

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                • #53
                  howson That is an interesting question. I would imagine if you draw enough water fast enough, it would be possible. If I am seeing the lines in the picture correctly, and allowing that there are no check valves. As long as one tank gets below the auxiliary fill line then you would pull air into the other tank? Not something I plan to test at least not intentionally. I will say that while filling with the auxiliary overflow capped of it never produced any pressure. All I used was a plastic cap with a paper towel to make it fit snug, not tight. It stayed in place while I finished filling the main tank. When I removed it, the overflow tube emptied and no additional water drained out.
                  2022 Momentum 397THS-R 12/3/2021
                  Traded 2021 Reflection 337
                  2020 Chevy Silverado 3500 DRW
                  Formerly M&K337

                  Comment


                  • #54
                    MK397THR, when you say you "finished filling the main tank", how did you determine it was full? Did you get water out of the main tank overflow?

                    The overflows on the freshwater tanks also act as air valves. Allowing air to flow out of the tanks as they are filled and allowing air to flow back into the tanks as they are emptied. If the overflow on the main tank is plugged, this tank will start to pressurize as the water level rises, compressing the air trapped into the tank. The effect of this pressurization is that the velocity of the water flowing through the connecting line to the auxiliary tank increases, meaning that tank will fill faster. Being smaller, the auxiliary tank would most likely then fill first.

                    Closing the auxiliary tank overflow and continuing to fill the main tank with its assumed plugged overflow will pressurize both tanks to some extent. Opening the auxiliary tank overflow back up will depressurize both tanks.

                    Of course, if water is flowing freely out of the main tank overflow on filling, then the above is all hog wash. Then I would have to wonder if the fill line is not actually split and is filling both tanks at the same time. Of course, this then raises the question of whether the fill line(s) are also the suction line(s) for the pump and if yes then why the smaller auxiliary tank isn't emptying first.
                    John
                    2018 Momentum 395M
                    2018 Ram 3500 Dually
                    Every day is a Saturday, but with no lawn to mow.

                    Comment


                    • #55
                      Confirmed on our 395MS-R that if I hook up city water to the power tank fill and let it fill until the rear aux overflow starts dumping, and then cap that overflow off, the power fill then forces all of that water into the main tank, and after a period of time, the main tank overflow tube(s) start to overflow.

                      The answer for us was a plastic shutoff valve on the aux overflow. I can now fill up both tanks completely full.

                      Hard to explain, but I did this after seeing pictures on facebook of how the tanks are connected. The power fill and aux tank fill both have what amounts to a a straighter shot to the aux tank, which means that the main tank inevitably fills slower.
                      Current: 2023 Grand Design Momentum 395MS-R. FBP, dual pane windows, 3rd A/C, heat pump, Fosgate, etc.

                      Truck: 2015 F350 DRW Platinum - Black.

                      Previous: 2021 Grand Design Momentum 376THS-R. FBP, dual pane windows, 3rd A/C, heat pump.

                      Comment


                      • #56
                        Originally posted by shaferz View Post
                        Confirmed on our 395MS-R that if I hook up city water to the power tank fill and let it fill until the rear aux overflow starts dumping, and then cap that overflow off, the power fill then forces all of that water into the main tank, and after a period of time, the main tank overflow tube(s) start to overflow.

                        The answer for us was a plastic shutoff valve on the aux overflow. I can now fill up both tanks completely full.

                        Hard to explain, but I did this after seeing pictures on facebook of how the tanks are connected. The power fill and aux tank fill both have what amounts to a a straighter shot to the aux tank, which means that the main tank inevitably fills slower.
                        Thank you all. This was a super helpful thread and I had no idea what was going on with tanks. Now I have an idea of fresh water tanks, at least....and I'll plug the aux overflow next time and I'm guessing the main overflow will soon "announce" it's location for me. I'm new to RV living. Next quest: Previous owner said he spent exorbitant amounts of time and effort to get the tank level gauges to work (even a little). No luck. He even drove around with tanks 2/3 full with detergent water, trying to get the sensors cleaned. No luck. Sensors are pretty useless to report tank levels. After emptying, a couple of them read 66%. Well, off to the next quest of understanding. Thanks for this thread!

                        My method for filling fresh water tanks will now be:

                        1) Fill from the main fill port (so all the water goes through the filter)
                        2) cap Aux overflow, once it starts flowing
                        3) shut off fill when main overflow starts draining.
                        Should have close to 140 gallons (plus the 12 in the hot water heater)

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                        • #57
                          Hobbit
                          It's rare to find someone that has tank sensors that are 100% reliable. The issue is a design flaw (IMHO).

                          Many on this forum have replaced the OEM sensors with the SeeLevel system. WondersAwait and ncitro are two members that come to mind. David's thread is here: https://gdrvowners.com/forum/operati...i-tank-sensors

                          RVGeeks has an article on the system if you'd like more information from a typically reliable source: https://www.thervgeeks.com/seelevel-tank-monitor/

                          Howard

                          Forum moderators are not GD employees--we are volunteers and owners presumably just like yourself. Unless specifically mentioned otherwise, we have nothing to gain should you choose to purchase a product or engage a service we discuss on this forum.

                          2017 Ford F-350 DRW, '19 315RLTSPlus

                          Comment


                          • #58
                            Originally posted by howson View Post
                            Hobbit
                            It's rare to find someone that has tank sensors that are 100% reliable. The issue is a design flaw (IMHO).

                            Many on this forum have replaced the OEM sensors with the SeeLevel system. WondersAwait and ncitro are two members that come to mind. David's thread is here: https://gdrvowners.com/forum/operati...i-tank-sensors

                            RVGeeks has an article on the system if you'd like more information from a typically reliable source: https://www.thervgeeks.com/seelevel-tank-monitor/

                            Howard
                            Thanks Howson. If I get really motivated, I'll put these tank sensors in. Read about them and appreciate the links!

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