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Tank layout for GD Momentum 395MS

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  • Tank layout for GD Momentum 395MS

    I find lots of documents online but I think they are all wrong (even the GD one.) What I need are the tank sizes for all my tanks. I know we have a fresh which is 140gal but how much is in the aux tank? It says the grey water is 104 Gal but that seems wrong. Also it says 104 gal of waste but I know it has two black tanks... what is the size breakdown?

    I can't find my manual but I suspect its wrong (or at least not precise) anyway given all the things I found online.

    Thanks!
    Todd & Steph
    2022 Momentum 395MS-R
    2018 Dodge Ram 3500 Laramie Diesel

  • #2
    Okay, this one gets a little complicated due to the dual water tanks, and the fact that the rear holding tank is split between the rear toilet, lav, and washer.

    Fresh Water:
    Total capacity 140 gallons
    Water heater = 12 gallons
    Main fresh tank shows P/N WT5641 which has a capacity of 98 gallons.
    So adding 12 + 98, that equals 110 gallons.
    140 - 110 = 30 gallons for the secondary tank. I can't find a part number to confirm this.

    There are three waste holding tanks on this rig. All of them are P/N HT466. The two black tanks have a sprayer, and the single gray tank does not.
    HT466 has a capacity of approximately 52 gallons. If you add those all up, it's 52+52+52 = 156 gallons.

    Now here's where it gets very confusing. The specs for your unit show 104 gray, and 104 gallons of black. But from what I see, you have 52 gallons of gray for the front, 52 gallons of black for the front, and 52 gallons of combined black/gray for the rear tank.

    The sole gray tank in the front of the rig is the repository for the kitchen sink, front bathroom sink, and front bathroom shower/tub.

    Also, I see that the 395MS is now limited to stock on hand, so it will no longer be manufactured.

    Jim
    Jim and Ginnie
    2024 Solitude 310GK
    GDRV Technical Forum Moderator
    GDRV Rally Support Coordinator

    Comment


    • #3
      Thanks.. this helps a lot! A secondary question... what is the best way to fill the fresh tank(s)? I can't seem to get the tanks to hold more than ~75% of capacity before the overflow starts.

      Also... what do you mean by "The two black tanks have a sprayer"
      Todd & Steph
      2022 Momentum 395MS-R
      2018 Dodge Ram 3500 Laramie Diesel

      Comment


      • #4
        Originally posted by bsonposh View Post
        Thanks.. this helps a lot! A secondary question... what is the best way to fill the fresh tank(s)? I can't seem to get the tanks to hold more than ~75% of capacity before the overflow starts.

        Also... what do you mean by "The two black tanks have a sprayer"
        As for "sprayer", I'm assuming that there is a black tank flush for the two tanks.

        Jim
        Jim and Ginnie
        2024 Solitude 310GK
        GDRV Technical Forum Moderator
        GDRV Rally Support Coordinator

        Comment


        • #5
          Originally posted by TucsonJim View Post

          As for "sprayer", I'm assuming that there is a black tank flush for the two tanks.

          Jim
          Indeed that is true. I was kind of hoping there was a magic clean button that included an internal pressure washer
          Todd & Steph
          2022 Momentum 395MS-R
          2018 Dodge Ram 3500 Laramie Diesel

          Comment


          • #6
            Back in 2018 when I called and emailed GD customer service about my tank capacity, they swore that I had two grey tanks, one front and one rear, and that is why my waste capacity was so high. Such is not the case. There is no rear grey tank for the washer and 1/2 bath sink, just a shared black tank. Something to think about if you plan on using a washer.

            As for actual tank capacity versus listed, there are many threads here that talk about how the overflow line taps into the side of the tank and how this affects the tank capacity.
            John
            2018 Momentum 395M
            2018 Ram 3500 Dually
            Every day is a Saturday, but with no lawn to mow.

            Comment


            • #7
              Originally posted by JBill9694 View Post
              Back in 2018 when I called and emailed GD customer service about my tank capacity, they swore that I had two grey tanks, one front and one rear, and that is why my waste capacity was so high. Such is not the case. There is no rear grey tank for the washer and 1/2 bath sink, just a shared black tank. Something to think about if you plan on using a washer.

              As for actual tank capacity versus listed, there are many threads here that talk about how the overflow line taps into the side of the tank and how this affects the tank capacity.
              Does this mean I will never really get the full compacity?
              Todd & Steph
              2022 Momentum 395MS-R
              2018 Dodge Ram 3500 Laramie Diesel

              Comment


              • #8
                I'm afraid not. To clarify post #6, I'm talking about the overflow on the freshwater tanks. It is possible to fill the grey and black tanks to capacity and beyond, but bad things can happen when you do this (water backing up into places you don't want it being the least of the problems), so it is good practice to empty these tanks before they are full.
                John
                2018 Momentum 395M
                2018 Ram 3500 Dually
                Every day is a Saturday, but with no lawn to mow.

                Comment


                • #9
                  Originally posted by JBill9694 View Post
                  I'm afraid not. To clarify post #6, I'm talking about the overflow on the freshwater tanks. It is possible to fill the grey and black tanks to capacity and beyond, but bad things can happen when you do this (water backing up into places you don't want it being the least of the problems), so it is good practice to empty these tanks before they are full.
                  Sorry... the clarity needed was from me. I meant the fresh tanks. I understand to never let my grey/black tanks to fill up
                  Todd & Steph
                  2022 Momentum 395MS-R
                  2018 Dodge Ram 3500 Laramie Diesel

                  Comment


                  • #10
                    Hi Todd,

                    I too have a M395MS 2021. I found that I could only put approximately 75 gallons of freshwater into the tanks and then the rear overflow hose for the rear freshwater tank would start to flow.

                    The best that I can tell is that the freshwater main tank is higher than the auxiliary freshwater tank in back. Since the tanks are connected the water will flow into both tanks until the rear auxiliary tank is full and then it will start to come out the overflow hose. My solution was to put a ball valve on the auxiliary overflow hose. I open the ball valve on the overflow hose for the auxiliary tank and then start filling fresh water through the main freshwater fill port. After about 75 gallons goes into the rig the auxiliary overflow hose will start having water run out. That’s when I close the ball valve on it and continue filling. At around 130-ish gallons the front overflow hose will start running water. That’s when I turn off the fresh water coming into the rig.

                    Rick
                    Rick, Steph, and Duke
                    2020 Chevy 3500 4 door High County DRW
                    2021 Momentum 395MS

                    Comment


                    • #11
                      bsonposh, yes. I'm afraid that is what that means. Some members have also reported lost of water from the freshwater tanks while traveling due to sloshing and others have had siphoning occur when their tanks start to overflow. Many threads here on these problems and solutions.

                      rickcwagner I can think of two reasons why the auxiliary tank begins to overflow before the main tank. One reason may be that the auxiliary tank overflow is mounted too low on the side of the tank. The other reason is that at some point between 2018 and now GD decided to branch the fill line to fill both tanks simultaneously (someone with a better memory or better at keeping track of such useful information will likely chime in with when this happened and what models this effected). Since the auxiliary tank is smaller than the main tank, it would fill first. I'm sure that you already open the ball valve on the auxiliary tank overflow after filling the main tank, to make sure that the auxiliary tank isn't pressurized.
                      John
                      2018 Momentum 395M
                      2018 Ram 3500 Dually
                      Every day is a Saturday, but with no lawn to mow.

                      Comment

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