Fresh tank fill

[Roy Lewis]

02 Marquis Tourmaline non tag. 40. When the fresh tank fill rocker switch is activated on Coach monitor panel the tank starts filling as its supposed to, however according to Coach Monitor Panel it fills ata. Much faster rate than it actually is and reaches full on panel it shuts off. For example we do a sink load of dishes and level drops 20 gal, a false reading to be sure.  What's going on?  Thank you in advance for any ideas.

[Dick Simonis]

I have been struggling with the very issue and spent quite a bit of time playing with it this past summer.  While we were at Mallard Creed for a couple of months I had noticed that every time I would fill the tank just a little bit of water use dropped the level to 75 gallons.  Since my normal method of operation is to fill the tank and use it for normal living rather than leave the water hose pressurized this was of interest.  First I went through the calibration steps but was unsuccessful in solving the issue.  So I picked up this gadget:

https://www.amazon.com/gp/product/B0058EOC5M/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1

to check how much was actually going into the thank before it shutoff.  No big surprise when it only reached 83 to 87 gallons from empty.  I also found out that the fill quantity may be affected by the level of the coach and, if fact, have had time when the tank would overflow and siphon out about 40 gallons.

No one seem to know exactly how the system operates but here is what I think.

The tank level is sensed by a pressure transducer mounted at one end of the tank or the other and measures the weight of the water in the tank.  This generates a 4-10 ma signal that give us our tank level reading.  This signal must also tell the valve to shut off but I don't think simply reading 100 gallons does it, I'm beginning to think the shut off valve is controlled by the mass reading of the transducer so when it senses the weight of 100 gallons of water it shuts the valve.  I have no idea if the full calibration affects this set-point or if it hard coded...I suspect the latter  and the designers intentionally fill it short to prevent overflow.

If indeed my suppositions are correct it would help explain why the tank occasionally overflows when the coach is leveled differently.  Since I have the manual leveling mod this is easily happens.  If, for example the transducer is at the front of the tank and the overflow at the rear and the coach is leveled slightly nose up than this is possible.  I don't have good data on this but when we get back to Lebanon this summer I'm going to play with it more...sort of entertainment.

I have no idea if I'm right but for the time being this is my working theory.