Fresh Water Capacity Force HD 37BH

[sconnors11]

So before getting into this, which is a negative experience, I'd like to point out that I love my Dynamax. Just about everything about it kicks butt

After taking the rig out to Glamis last weekend and practicing full water rationing, the water went pretty quick. The wife asked if I could do anything and I measured things, planning on adding a second 50 gallon fresh tank (and maybe grey) to bring fresh water capacity back to the 150 gallons my old 5th wheel had.

I measured the existing tank in my 2017 Force HD 37BH and came up with the following dimensions:
47.5 x 25.5 x 18
This gives 21,800 cubic inches which is 94.3 gallons, close enough to 100 gallons, right? (Though it doesn't account for wall thickness.)

Not so fast. The bottom of the overflow is 15.5 inches from the bottom of the tank, so filling the tank any higher than that will cause it to drain out the bottom. As a matter of fact, if you fill it to the bottom of the overflow, it'll leak as you drive down the road. I was pulled over a couple of weeks ago because someone thought I might be leaking gas. Fun stuff...

So, the revised dimensions are:
47.5 x 25.5 x 15.5 This gives 18,775 cubic inches or 81.3 gallons. There are 6 2" vee shaped cutouts around the tank that bring it down to 80 gallons.

This tank has the same nominal dimensions and is advertised as an 80 gallon tank.
80 Gallon Rv Water Tank - RVB327

Okay, I think, order a bigger tank and get on with life...

This 100 gallon tank will work, but it's over 500 bucks before shipping:
WH-2100-3 - Trionic 100 Gallon Marine Grade Tank

This is the tank that I'd want at 130 gallons, but its over 700 bucks before shipping:
130 Gallon Rv Water Tank - RVB356

I have to admit, I'm disappointed that I didn't get what I was sold. I dry camp a lot during winter months. The 100 gallon tank was going to be borderline usable as it was. To loose 25% of that (before sloshing, which I can address) is a real kick in the boys.

Can anyone else with a Force or Force HD measure their tank and post up the dimensions? Maybe I got the wrong one? I find that hard to believe, as all the bracing looks made to fit.

[FOURWHL]

I've noticed the same with sloshing/overflow. Havent measured mine exactly but would guess water stops 2" from the top of the tank. Been thinking about a valve that can be closed when driving to eliminate the sloshing. Should be able to hold a couple more gal that way.

[bclemens]

We typically list the water capacity that is stamped onto the tank. I'm on vacation this week, but have an email into engineering to double check that. Also to see if there is a way to move the overflow to the top of the tank or if that creates any issues.

[bclemens]

It's an 0602W which is listed at 97 gallons.

[sconnors11]

Originally Posted by bclemens

It's an 0602W which is listed at 97 gallons.

Unfortunately, the measurements and calculations do not agree with the stamp. Where can I find the stamp on mine? Which manufacturer do you generally use?

I didn't account for rounded corners or wall thickness in the calcs to give the benefit of the doubt to others. I have one of those hose meters on the way from Amazon to see what I can really get into the tank.

I have attached a picture of the overflow. It is facing the front of the RV, so every time the RV decelerated or was nose down a bit of water would leave the tank.

The short term solution is to put a pipe plug or shutoff valve where the overflow comes out of the tank. At least that way I can eliminate water leaving the tank once max level is established (~80 gallons). I believe the tank is still vented through the other hose seen in the attached picture.

I assume there is an air gap allowance for expansion/contraction of the water. I know that's a design consideration in API 510 at the refinery.

I'm guessing after the 4 hour drive to Glamis we had less than 70 gallons in the tank. We left with at least 10 gallons still in the tank, so 50-60 gallons lasting 4 nights/4 days with 4 adults and two toddlers sounds about right. We used paper plates and bowls... I only allowed 3 Navy showers.

At least now I know why I leave a trail of water wherever I go for the first few hours after topping off the water

This all started because I wanted to get measurements to make a strapping chart on the side of the tank and see if there was room to add a tank for additional capacity. Remember, I love the rig!

[Jetjockey6]

Amen, brother! Your question is an interesting one. I have a 2015 Force 37BH and just measured the tank. My numbers are exactly what you published. To make it worse I was told that the tank holds 110 gallons when I bought the rig.
Hmmmm. Additionally, with all the curves and such molded into the tank it can’t come even close to the claimed 100 gallon capacity. Your 80 gallon figure is most likely more accurate than the factory number.
One thing to remember if you install a larger tank is not only the additional weight of the water when the tank is filled but having that much more weight so far back in the rv just might add a handling/balance issue. If the 130 gallon tank is installed, and filled, you are looking at another 50 gallons or over 400lbs more weight. In a 28,000lb rig that isn’t a huge number BUT where it is placed, all the way in the back of the rig, might generate an issue. Sloshing water generates
energy/momentum so you might want to rethink the larger tank. An overflow
shutoff valve is a good idea considering the size of your family.
I have had my 37BH for almost three years. Other than the usual factory-generated quality control issues the rig has performed well in all kinds of weather, rv parks and so forth. I would caution anyone buying a 37BH not to leave the dealer area until several thousand miles of vigorous “shakedown” have been accomplished. Mine required a month at the factory for a major rebuild of the aft bedroom then,after a few months on the road, three weeks at the selling dealer to fix all the resulting QC issues overlooked by the factory. Not unexpected with any rv but a few extra hours of quality control at the factory would have prevented most of the issues.

Jim

[sconnors11]

Originally Posted by Jetjockey6

...
One thing to remember if you install a larger tank is not only the additional weight of the water when the tank is filled but having that much more weight so far back in the rv just might add a handling/balance issue. If the 130 gallon tank is installed, and filled, you are looking at another 50 gallons or over 400lbs more weight. In a 28,000lb rig that isn’t a huge number BUT where it is placed, all the way in the back of the rig, might generate an issue.
Jim

Jim,

Thanks for taking the time to measure your tank. I appreciate it.

If the factory is advertising 100 gallon capacity, then the weights and measures calcs should be reflecting that. I'm looking at adding 30 gallons, or 240lb, to what has already been calculated.

Hey, on another note, I may have just found some additional CCC!!!

[sconnors11]

I think this is a link to the tank referenced above:
https://www.rvpartsnation.com/rv-plu...-48-x-26-x-18/

[Jetjockey6]

I was looking at it from the more practical standpoint vis a vis handling/balance. If you cannot get more than 80 gallons into the OEM tank and then replace it with a tank which will really hold 130 gallons the difference would be about 400lbs driving out of the driveway. In an rv almost 40’ long that could amount to
some serious lateral momentum when cornering. Perhaps not, but having flung my toad
almost 75 degrees off the turn radius this past winter when making a routine, but surprisingly slippery slow speed turn I thought the kinetic energy issue was worthy of bringing up.
On another subject...what engine is in your 37BH and what level of fuel mileage are you seeing? Have you weighed your 37BH at a truck stop?

Jim

[Jammer151]

Sconnors....same here. We just spent our first full two weeks in the Mojave and I had to drive into town and get 30 gallons to make it. Never had to do this on my toy hauler which had a 120 gallon tank. Told my wife there was no way our tanks hold 96-100 gallons as advertised....regardless what the stamps on them say. As a matter of fact I was going to get a meter during my next fill to really see how much it will hold.

I was looking at getting one custom made to replace the one under the bed...filling up all the open/free space. Talked to the factory that was going to make the mold for it, with baffles in it, and they said it would give me around 160 gallons. However, they wanted $6K to build the mold so I opted to not go down that road yet.

Per Jim’s concerns on weight, fully loaded, including enclosed trailer hooked up, I’m at 19,680 on my drive axle, so adding ~500 keeps me below the rear axle rating.

Looks like either trips to town or bring extra water tanks for now. The Renegades have 150, two 75 gallon tanks.

[Magnatudes]

If you haul a trailer, maybe you can add a barrel tank to it and invest in a small/cheap transfer pump. I did that when we would spend 6 weeks at Lake Powell. Had a rolling wastewater tank for portable dumping into the nearest portajohn. It's been too many years-gone-by so I dunno about Glamis but they may have a dumpstation by now.

[Jammer151]

Originally Posted by Magnatudes

If you haul a trailer, maybe you can add a barrel tank to it and invest in a small/cheap transfer pump. I did that when we would spend 6 weeks at Lake Powell. Had a rolling wastewater tank for portable dumping into the nearest portajohn. It's been too many years-gone-by so I dunno about Glamis but they may have a dumpstation by now.

Yes and a lot cheaper....BTW, we love love love our Dynamax.

[Magnatudes]

Originally Posted by Jammer151

Yes and a lot cheaper....BTW, we love love love our Dynamax.

We loved our Country Coach when we had it. Nothing like a Cummins ISL and a real chassis with a real quiet variable-speed diesel gen. If we had the place to store one, we would have gone with a full-on Dynamax. Downsized now. Hoping for a future short DynaQuest 264ST

[Bob Maager]

I have a similar problem. Last July we bought a 2017 Forest River Wildwood 32 ft. travel
trailer. First time out we ran out of water. There are only two of us and two dogs. We had an older model Fleetwood. We never ran out of water. When we got home I decided to see how much this 40 gallon water tank holds. I filled the tank and drained it in a 5 gallon bucket. I came up with 30 gallons. I complained to the dealer I bought it from, they were going to contact Wildwood about it. They checked it and came up with 35 gallons. Haven't heard anything sense last August. I did put a shut off valve in the over fill line. I added maybe another two gallons. That helped with the sloshing out when traveling. We only went out twice with it. I m real couscous about using water now.
Bob

[sconnors11]

I was able to use the new hose meter to get an idea of how much water the rig would accept before leaking out the overflow this evening:

-Everything was kept stock, as received.
-RV was leveled before testing, kept still.
-Water was drained from the tank and the pump was run until it spit and would not stop when the faucet was turned off.
-The orbit flow meter was placed on the end of the hose and a quarter turn valve with a bit of hose on the tip.
-The meter read 73.1 gallons when the first trickle came out of the overflow.
-A bucket was placed under the trickle and I'll report how much is in it in the morning.

Jammer, I wouldn't have a custom tank made... It'll be cheaper to buy a smaller tank, ~75 gallon, maybe, and give the two common vents and drains. This'll eliminate the need for a baffle, too.

Tomorrow I'll plug the overflow and see what that does to capacity. For now, goodnight...

[sconnors11]

I checked the 5 gallon bucket this morning and there wasn't much more than a quart in it.

The plan tonight is:
- Get a plug for the overflow
- Drain 5 gallons into a bucket
- Install the plug without getting the under-bed area wet
- Fill until it makes sense to stop.*
- Subtract the 5 drained gallons from the total number of gallons used.

* Note: On the Gearbox, there was a definite change in sound when the top of the tank was reached. I'm hoping the same will be the case here.

[Jammer151]

Wow...73, that is a significant variance. It will be interesting to see what difference plugging the overflow will make.

Thank you for doing this.

[sconnors11]

Sorry for the delayed update.

-I installed a 1.25" pipe plug in place of the overflow.
-Tank was completely drained, same procedure as before.
-Using the gravity fill outside the rig, was able to fill almost 1/2" higher (74.5 gallons)in level before the sound changed (water level rose above vent fitting) -I continued to fill for a bit more, but stopped when water started to mildly spit out. I honestly didn't feel comfortable taking a chance to pop a fitting off and get everything wet under the bed.

Ended up with the overall level 1" higher than before the plug was installed (77 gallons) It looked like there was another inch of air in the tank.
That additional inch should give another 5 gallons if filled. It looks like the tank might hold 81 or 82 gallons with no vapor space in the tank.

Now for the good news! I drove the rig to run an errand and there was no overflow sloshing! This is the first time I haven't left a snail trail after topping off the fresh water tank. Pretty stoked about that.

There isn't all that much to be gained in capacity by plugging the overflow, maybe 4 or 5 gallons, but the lack of slosh loss should save at least that amount. I think its probably a 8 to 10 gallon difference from fill-up to camp. That's worth the cost of a dollar plug and some PTFE tape and 15 minutes of effort.

It's still a bit of a hard pill to swallow that there's no way to get much more than 80 gallons into a "100 gallon" tank. I'm not sure about the accuracy of the meter I used, so I would encourage others to do their own testing. Maybe a factory test on an uninstalled tank? The numbers from testing align with the strapping chart calculations (~4.9 gallons per inch).

Please ask questions and comment with your own experiences.

Sean

[LTZ470]

Thats the saddest part about Dynamax for sure...Just got rid of a 2004 Komfort Karry-All Toy Hauler, had over a 100k miles and held 136 gallons Fresh Water, 90 gallons of grey water in two separate tanks (one kitchen + one bath), 55 gallons of Black Water...

One thing I did do to increase the capacity due to the suction being 4" from the sagging tank bottom: I drained the tanks (2), pulled off suction lines on the side of the tanks then threaded the inside of the suction line, added a 12" high quality hose with a brass strainer/check valve that was heavy enough to keep the suction strainer in the lowest part of the tank, originally it would take up to 19 gallons to get suction with water pump, after this modification only 7 gallons were require to acquire suction on water pump...12 gallon gain in capacity...these tanks were laid flat and the center of the bottom sagged significantly in the center...

[sconnors11]

Originally Posted by LTZ470

Thats the saddest part about Dynamax for sure...Just got rid of a 2004 Komfort Karry-All Toy Hauler, had over a 100k miles and held 136 gallons Fresh Water, 90 gallons of grey water in two separate tanks (one kitchen + one bath), 55 gallons of Black Water...

One thing I did do to increase the capacity due to the suction being 4" from the sagging tank bottom: I drained the tanks (2), pulled off suction lines on the side of the tanks then threaded the inside of the suction line, added a 12" high quality hose with a brass strainer/check valve that was heavy enough to keep the suction strainer in the lowest part of the tank, originally it would take up to 19 gallons to get suction with water pump, after this modification only 7 gallons were require to acquire suction on water pump...12 gallon gain in capacity...these tanks were laid flat and the center of the bottom sagged significantly in the center...

One thing I did notice in testing is that there was no observable level in my tank when it was sucked dry. The last 4 gallons or so involved continuous running of the water pump and spitting as signs of low water. I look at this as a positive. First, all the water was ultimately pumped from the tank, and second, if you're in the shower and the flow starts spitting, you have a bit of time to get the soap out of your eyes before the water completely shuts off.

Lets focus on the easy fix to slosh flow. I love my Dynamax.