Filling fresh water tank through overflow vent tube

[MBK]

I have a 26 foot cougar with a 40 gallon freshwater tank. The tank was about 1/3 full when I tried to manually fill it by pouring water through a funnel into the Overflow vent. It only took about six gallons and then Water started backing up out through the vent as if it was full. The level indicator shows the tank at about two-thirds full. Based on all the above information I would have expected to be able to put more water in the tank before it overflows. Has anyone run into this problem before when trying to fill the freshwater tank by manually pouring water into the Overflow vent tube. Thank you

[chuckster57]

Welcome to the forum!!

With the placement of the level sensors, it possible that you tank level was just below the 2/3 sensor. How much water did you add before it started to pour out the vent tube?

If your trying to verify water capacity, the water heater is included in the listed spec.

[MBK]

Hi Chuckster

Tank level showed about 1/3 full prior to my attempt to fill it. I was able to pour 6 gallons down the vent tube before it started backing up. The Tank level now reads about 2/3 full.

[ctbruce]

Are you level side to side and front to back?

[MBK]

Yes. I am level fore-aft and side to side

[chuckster57]

And what happens if you fill using the fill port?

[JRTJH]

Most "under floor" fresh water tanks are not very tall. As an example, a 50 gallon tank may be 52" long, 30" wide and only 6" tall. They "lay" between the frame rails and are surrounded by bulkhead fittings. With the tank being around 6" tall, if the trailer is "off level" just 1" in the 96" width of the trailer, you'll reduce the accuracy of the tank sensors about 15%. That is, IF (a very big assumption with any RV) the tank sensors are 100% accurate.

So, if you've got a 50 gallon tank and you're 1" low on the road side when filling, the gauges may read "full" with 42 gallons of water in the tank. Shift the trailer to 1" low on the curb side and your gauges may read 2/3 full (around 33-34 gallons) even though the amount of water (in gallons) is unchanged. The "status indicator panel" is a very "rudimentary device" that's best used as a means to get an approximate idea of tank level status. It'll never (ever) give you an accurate status, especially if your trailer is "just the slightest bit off level.

[Steveo57]

If the overflow line runs for any distance to the tank it may have a high point that can form a loop seal. That can prevent the tank from venting after you put enough water in. I don't know how your tank is situated with regards to the overflow point but it's something I've heard of happening to others.

One case I remember was when the tank was located in the rear of the trailer and the overflow was towards the front. The vent line ran along the frame and it had a high point which when the line got filled up it the tank couldn't vent and the guy couldn't get any more water to go in.

[Snoking]

Where is the air in the tank suppose to go when you pour water in the vent?????

Put the trailer over your shoulder and pat it on the back. Might want to wear your rain gear while doing this. Chris

[NH_Bulldog]

I wouldn’t trust the tank gauges. On mine, the tank is only as deep as the frame rails - 8” or so. Like JRTJH said, just a little off level and gauge reads wacky.

Consider these two experiences from a recent long trip with no water connection:
My parent’s motor coach has a visible tank in the side compartment. The 1/3 sensor is halfway up the tank, the 2/3 sensor is 3/4 up and the full sensor about an inch from the top. This means that the tank shows empty until it reaches the half full point but the gauge shows only 1/3 full. When it reads full, there is still room for more.

On My 43 gallon tank the gauge read 1/3 full, I filled 4 water cans (6 gallons each) and could only get 2 1/2 cans in.

My routine on trips now is that I drain the tank before we leave, then add 6 gallons for road use. If we are boondocking, we typically plan on 6-8 gallons per day and fill accordingly.