Question about the Fresh water tank size.

[Randy E]

Hello.
We have a 2017 3791RD. On the spec sheet and on the data sticker on the coach it says 66 gallons of fresh water capacity. But today I finally bought a small inline water meter to measure how much water I put it. We normally only carry less than half a tank due to weight. As I’m filling the fresh water tank today, water starts flowing out of the overflow tube on the back at exactly 44 gallons. The tank was empty because I just emptied it and let it drip dry. The RV was level too. Why does it say 66 gallons when it only holds 44? Even if I add the hot water tank in, it doesn’t add up to 66 gallons.

[Foldbak]

Originally Posted by Randy E

Hello.
We have a 2017 3791RD. On the spec sheet and on the data sticker on the coach it says 66 gallons of fresh water capacity. But today I finally bought a small inline water meter to measure how much water I put it. We normally only carry less than half a tank due to weight. As I’m filling the fresh water tank today, water starts flowing out of the overflow tube on the back at exactly 44 gallons. The tank was empty because I just emptied it and let it drip dry. The RV was level too. Why does it say 66 gallons when it only holds 44? Even if I add the hot water tank in, it doesn’t add up to 66 gallons.

Supply chain shortage? I guess not in 2017. Did you buy it new? Maybe the previous owner changed it? Maybe Keystone ran out of 66 g tanks and installed what they had? (They'll never know)

[DutchmenSport]

Yes, that sounds about right. Mine is right at 45 gallons when filling the same way and it advertised as 60 gallons. So.... where's the extra gallons at?

First, to the 44 gallons in the tank, they add the size of your water heater. If you have a 10 gallon water heater, that number is now 55 gallons. Now, add the amount of water that is actually inside the water lines inside your camper, probably 2 gallons or more. Now you are up to 57 gallons your camper water capacity has.

THAT's how they figure the fresh water capacity size!

Also, remember, even though your fresh water tank may have been emptied by the drain valve, it still holds 2 -4 gallons (or more) of water that never leaves the tank. And if you use your on-board water pump to pump the water, it's possible that amount that never gets pulled out of the tank could be as much as 5 extra gallons. There is your extra gallons.

[Foldbak]

Originally Posted by DutchmenSport

Yes, that sounds about right. Mine is right at 45 gallons when filling the same way and it advertised as 60 gallons. So.... where's the extra gallons at?

First, to the 44 gallons in the tank, they add the size of your water heater. If you have a 10 gallon water heater, that number is now 55 gallons. Now, add the amount of water that is actually inside the water lines inside your camper, probably 2 gallons or more. Now you are up to 57 gallons your camper water capacity has.

THAT's how they figure the fresh water capacity size!

Also, remember, even though your fresh water tank may have been emptied by the drain valve, it still holds 2 -4 gallons (or more) of water that never leaves the tank. And if you use your on-board water pump to pump the water, it's possible that amount that never gets pulled out of the tank could be as much as 5 extra gallons. There is your extra gallons.

Your so smart Dutch! Learn from you all the time.

[Randy E]

I am the first owner. I bought it brand new in 2017. I always wondered about it. It just did not appear to hold as much as it should.

[Daryles]

I just got done de-winterizing today. Rig was bone dry. I also have an inline water meter.
Flushed the water heater with a Camco rinse wand. Cleaned and put the anode rod in.
I had to sanitize the system so I poured 2 cups of bleach (2 cups for 64 gallons of freshwater to sanitize) in the water hose and connected it to the city water - FILL. Turned "ON" the water heater bypass (don't want the bleach going into the water heater until it's mixed properly). Started filling the tank.
At 42 gallons I turned off the hose and turned on the water pump. I turned OFF the water heater bypass and opened the pressure relief valve to let the air out. Once bleach water started coming out I turned off the relief valve.
I turned the water hose back on and continued filling the freshwater tank. I went inside and opened each faucet to get air out of the pipes until I smelled bleach water, then closed the faucets.
Finally water started coming out the freshwater tank vent. I turned off the water hose.
The water meter read 66 gallons.
So.

50 gallons freshwater
12 Gallons water heater
4 gallons in the pipes.

Normally during a regular freshwater tank refill it overflows at 42 gallons.