Water Pump Won't Pump with 1/3 Full Tank

[BrokeDown]

Interesting thread.

My 2022 351MS is sucking air, and the tanks are full. I pulled the tank line off of the Nautilis and sucked on it... nothing but air.

Was the belly shield hard to drop? Did you have to start at one end?

Thanks
John

[FT4NOW]

Interesting thread.

My 2022 351MS is sucking air, and the tanks are full. I pulled the tank line off of the Nautilis and sucked on it... nothing but air.

Was the belly shield hard to drop? Did you have to start at one end?

Thanks
John

Could be a bad check valve on inlet of city water connection or a loose or cracked strainer that is on the inlet side of pump. Other option could be the pump needs to be primed.

[BrokeDown]

The line that I tested goes directly to the tank. The problem must be in that line. To troubleshoot further, I need to drop the belly shield to gain access to the pipe and tank.

[FT4NOW]

The line that I tested goes directly to the tank. The problem must be in that line. To troubleshoot further, I need to drop the belly shield to gain access to the pipe and tank.

There is only 1 line going to the FW tank. It is used to fill and take suction from the tank. If you have a valve or some other component letting air in the flow path, you will not get a suction from the pump. Might want to try sanitize or winterize mode with a shore hose in a bucket of water to get the pump primed and then switch to dry camping and see what happens. If that doesnt work, I go by my previous suggestion.

[BrokeDown]

Agreed... except, I completely disconnected the fill line from the Nautilus so nothing else is in play. I connected the fill line to directly to two different pumps... no water. I put my mouth over the line and blew in and then drew out. That line has no water in it. So there is a break in the link somewhere after the link goes under the floor.

BTW: both pumps will draw water from a bucket.

-B

[FT4NOW]

Agreed... except, I completely disconnected the fill line from the Nautilus so nothing else is in play. I connected the fill line to directly to two different pumps... no water. I put my mouth over the line and blew in and then drew out. That line has no water in it. So there is a break in the link somewhere after the link goes under the floor.

BTW: both pumps will draw water from a bucket.

-B

Well, now that you say all that, makes sense.

Strange you could fill the tank up, or was it filled from dealer?

If it wasnt you that filled it, maybe it's not actually full and there is a sensor problem. If it wasnt you that filled it, have you opened the tank drain at all to verify it has water.

If it's a clogged fill or vent line, i would think there would be trouble filling the tank.

[lmlayfield]

Well, now that you say all that, makes sense.

Strange you could fill the tank up, or was it filled from dealer?

If it wasnt you that filled it, maybe it's not actually full and there is a sensor problem. If it wasnt you that filled it, have you opened the tank drain at all to verify it has water.

If it's a clogged fill or vent line, i would think there would be trouble filling the tank.

I spent hours under my Momentum 21g with the coroplast off watching the water levels as I filled the tanks (there are 2 tanks connected together) and trying figure out why 20+ gallons will not pump out.

Brokedown and FT4NOW - there are three “lines” into each of the 2 freshwater tanks on a Momentum. 1 output line used to pump water. These two lines are T’d together before they go to the pump. 1 input line used to fill the tank that is mounted higher than the output line. And 1 overflow output line at the top. There is also a dump valve for each tank. In the picture you can see the lower pump line outlet, the higher fill line, and the dump valve. So as you diagnose your problem make sure you take this configuration into account.

If you take careful note of the pump line location you will see that it is a couple inches above the bottom of the tank. This measurement increases as you move to the middle of the tank where there is a “belly” due to the weight of the water. I am fairly certain this is the reason I cannot pump the last 20+ gallons from my tanks. Water does not flow uphill. Everything works just fine as long as there is 25 gallons or more on board.

I assume one possible fix is to spin weld another pump outlet fitting in the bottom of the tank and plug the original one. The second picture is my thought for a location. Anyone ever spin weld a fitting from the bottom with an empty tank in place? There is not enough room to shim the tanks on the far side so the water flows to the outlet. One side support of each tank is a welded crossmember so moving the tanks supports in any way is out. Any other ideas?

Grand Design has a ton of photos and videos of my issue. Waiting on their proposed resolution. Would love to have a list of good ideas to discuss with them so please share your thoughts.

[FT4NOW]

@lmlayfield the 3 lines might be if you have dual FW tanks to properly equalize and fill them. My 399 only had a single tank, and only a single line attached to the tank not counting the vent line. Mine was a 2017, so perhaps things changed. Maybe that's the issue with his pump, one of those other lines could have an issue. Not sure if he has a 2nd FW tank though.

[lmlayfield]

@lmlayfield the 3 lines might be if you have dual FW tanks to properly equalize and fill them. My 399 only had a single tank, and only a single line attached to the tank not counting the vent line. Mine was a 2017, so perhaps things changed. Maybe that's the issue with his pump, one of those other lines could have an issue. Not sure if he has a 2nd FW tank though.

After more time analyzing and months at a dealer, I have confirmed the source of my issue. This is true whether you have one tank or two. The problem arises because my tanks are supported by the shoulders only. There is no rigid support underneath the tanks. There are three flimsy metal straps that do not even touch the bottom the tanks when they are empty. These straps are screwed to the cross frame members and under stress they can stretch and the screw holes elongate. The tanks are 60” wide (left to right in the frame) 42” long (front to back) and the depth varies from about 4” on the passenger side to about 7” on the driver side. The tank bottom slopes towards the tank outlets on the deeper driver side. Can you imagine a plastic bottom with these dimensions supporting the weight of nearly 50 gallons of water? Even if the metal straps were once tight, they have long since stretched, along with the tank bottom. Both my tanks now have a “belly” that sags below the water outlet. Thus 25 gallons are not reachable by the pump. Even worse, most of this unreachable belly water is not able to be dumped by the dump valves. In short, everything works fine with the water system as long as there is more than 25 gallons on board. With 25 gallons left it is all sputter and no water pressure.

This problem was not noticeable when my unit was new. It developed over time as I traveled with water in my tank. The 21g being a toy hauler with a generator, it is reasonable for Grand Design to expect owners of these units to travel with full tanks to use their toys in boondock type camp locations. Hauling with water weight caused this problem to occur. I did notify GD before my 1 year warranty was over, but I am still facing challenges. This is not a case of something breaking on my rig. If you replace my water tanks with brand new ones of the same design, these new ones will fail too. I have been to three dealers and a mobile tech so far. The first one replaced the water pump. The second one ordered one new water tank. It was backordered so after sitting for three months I pulled my unit and told GD I was going to get a mobile tech since I did not believe it was a water tank issue. The mobile tech and I pulled the coroplast and discovered this issue. When I informed GD they did not believe me and told me a dealer had to repair this issue. The third dealer agreed with my diagnosis of the problem and used plywood and 2x4s to support the tank bottoms using the same flimsy metal straps. I have rejected this repair as insufficient. I agree it will work for a short time, but the straps will stretch again and the untreated wood will get soft and rot and the problem returns. Now GD wants me to take it to a dealer they recommend in Indiana (I’m in Alabama).

If your unit has a shoulder type tank(s), your issue is likely just like mine. You should drop the coroplast so you can visually see the water outlet and bottom of your tank(s). I think many of the owners are likely not even aware of this issue. Their problem may not have progressed as far as ours, maybe they use water hookups for much of their camping, or maybe they just don’t keep track of their water usage and assume the tank is empty. Not only do these unsuspecting owners have potentially a couple hundred pounds of water they are unaware of, they may not know there are gallons of fetid water or bleach water sitting in the fresh water tank that cannot be dumped. Whether you just cleaned your fresh water system or you thought you dumped the water out after your trip 2 weeks ago, you are adding fresh water to drink to a tank that maybe you shouldn’t be drinking from.

[Boom 'r Bust]

After more time analyzing and months at a dealer, I have confirmed the source of my issue. This is true whether you have one tank or two. The problem arises because my tanks are supported by the shoulders only. There is no rigid support underneath the tanks. There are three flimsy metal straps that do not even touch the bottom the tanks when they are empty. These straps are screwed to the cross frame members and under stress they can stretch and the screw holes elongate. The tanks are 60” wide (left to right in the frame) 42” long (front to back) and the depth varies from about 4” on the passenger side to about 7” on the driver side. The tank bottom slopes towards the tank outlets on the deeper driver side. Can you imagine a plastic bottom with these dimensions supporting the weight of nearly 50 gallons of water? Even if the metal straps were once tight, they have long since stretched, along with the tank bottom. Both my tanks now have a “belly” that sags below the water outlet. Thus 25 gallons are not reachable by the pump. Even worse, most of this unreachable belly water is not able to be dumped by the dump valves. In short, everything works fine with the water system as long as there is more than 25 gallons on board. With 25 gallons left it is all sputter and no water pressure.

This problem was not noticeable when my unit was new. It developed over time as I traveled with water in my tank. The 21g being a toy hauler with a generator, it is reasonable for Grand Design to expect owners of these units to travel with full tanks to use their toys in boondock type camp locations. Hauling with water weight caused this problem to occur. I did notify GD before my 1 year warranty was over, but I am still facing challenges. This is not a case of something breaking on my rig. If you replace my water tanks with brand new ones of the same design, these new ones will fail too. I have been to three dealers and a mobile tech so far. The first one replaced the water pump. The second one ordered one new water tank. It was backordered so after sitting for three months I pulled my unit and told GD I was going to get a mobile tech since I did not believe it was a water tank issue. The mobile tech and I pulled the coroplast and discovered this issue. When I informed GD they did not believe me and told me a dealer had to repair this issue. The third dealer agreed with my diagnosis of the problem and used plywood and 2x4s to support the tank bottoms using the same flimsy metal straps. I have rejected this repair as insufficient. I agree it will work for a short time, but the straps will stretch again and the untreated wood will get soft and rot and the problem returns. Now GD wants me to take it to a dealer they recommend in Indiana (I’m in Alabama).

If your unit has a shoulder type tank(s), your issue is likely just like mine. You should drop the coroplast so you can visually see the water outlet and bottom of your tank(s). I think many of the owners are likely not even aware of this issue. Their problem may not have progressed as far as ours, maybe they use water hookups for much of their camping, or maybe they just don’t keep track of their water usage and assume the tank is empty. Not only do these unsuspecting owners have potentially a couple hundred pounds of water they are unaware of, they may not know there are gallons of fetid water or bleach water sitting in the fresh water tank that cannot be dumped. Whether you just cleaned your fresh water system or you thought you dumped the water out after your trip 2 weeks ago, you are adding fresh water to drink to a tank that maybe you shouldn’t be drinking from.

Tripp,

Thank you for your well written, easy to understand, and detailed follow up!

The potential magnitude of this desgn flaw is huge. I feel like this is enough of a potential health hazard that it needs to be "shouted from the mountain tops."

Reading your story makes me want to drop my coroplast for an inspection. And that is a job I have succesfully avoided for 4 years with 2 rigs...

Thanks to your significant efforts, we now have a confirmed and wide reaching cause to the issue I started in this thread.

Boomer