2004 Fleetwood Discovery Accurate Fresh Water Monitor
As you're probably already aware, the fresh water tank level indicator lights can be way off the mark. The penalty for reading too high means you run out of water when you need it, and the penalty of reading too low can be overfilling the tank (warping the floor of the coach) or dragging around hundreds of extra pounds of deadweight, so there's a genuine need for a truthful level gauge. Having to traipse back and forth into the coach to check the level while filling (trying to remember not to get sidetracked while the tank overfills) is a pain. Finally, measuring only in quarters of a tank is pretty crude, even if everything worked as advertised. On our coach, the fresh water monitor indicates about half full when the tank is empty. The other level gauges seem to closer to the mark.
Our coach didn't come with any documentation for the built-in level metering system, so if there's a re-calibration process possible, we don't know about it. The Discovery Owner's Manual only says that if it is incorrect, it can be because something is hanging on the sidewall in the tank, which is not likely for a completely filtered fresh water system as ours is, except for perhaps a thin layer of algae.
I originally thought we could simply attach a clear hose to the Cold Water Drain and view the tank level from that connection, but after I mapped out the fairly complicated circuit (click here for a diagram), I realized that the drain is part of the pressurized circuit, so that won't work. But because the tank connection to the rest of the system (marked on the diagram) is through a standard 1/2" threaded connector in the utility compartment, it's easy to add a small monitor tap to the line.
The weight of a column of water is about 0.43 PSI per foot of height. A pressure gauge located near the bottom of the tank would show roughly 0-0.2 PSI from an empty to a full tank. Using a dial gauge would have been a great solution, because you can get gauges that read 0-10 inches of water, and the added circuit would be completely sealed and maintenance free. However, tapping into a line shared by the water pump inlet (causing a mild in-line vacuum when it runs) and the by-pass valve (which when opened and the tank was full might cause up to +60 PSI) means that this sensitive gauge would have to live through those extremes. One manufacturer stated that their gauges cannot take the range. Adding a new tap to the tank might solve this but I can't see where you could do this easily because the tank is buried in the chassis.
So what we've got now is a small clear PVC tube that is mounted vertically on the water panel, and we've labeled the level in quarters but you can see the exact measurement. There is a shut-off valve that has to be opened first for a reading, and then closed after measuring the level. And you can't use the gauge and fill from the city water connection simultaneously. But at least you can get an accurate reading when you need one.
All you need for this is:
1/2" pipe thread male-female extension with a 1/8" tap (Watts A-851)
Adapter from male 1/8" threads to 1/4" quick connect (Watts PL-3004)
Add some Teflon tape, a couple of clips or nylon ties and adhesive pads to hold the hose and valve in place, some Dymo labels and you're set, after spending less than $20. No holes required. Connection Gauge
You can calibrate the level heights yourself. Make sure the coach is level and run water out of the Cold Water Drain until the water pump can no longer provide a solid stream of water. Mark the level against a ruler, preferably metric so you don't have to deal with fractional inches (click here for the setup). Fill the tank through the gravity feed until it overflows, then blow out a couple gallons so you don't include the filler hose in the height measurement. I found that the water tank is largely rectangular (the level rises uniformly with a constant fill rate), and is about 4-3/4" (12mm) deep. If you want to skip the calibration mess and trust my measurements, mark the following points measured from the bottom of the black panel where the controls are mounted: 8-1/4" = Empty, 9-3/8" = 1/4 tank, 10-5/8" = 1/2 full, 12" = 3/4 full, and 13-1/8" = full. Or you could mark off gallons at any increment between the empty and full marks (every 15 gallons might make sense because it's a 90 gallon tank).
As far as accuracy goes, the level of the coach will have a definite effect because of the shallowness of the fresh water tank. The Power Gear hydraulic leveling system will keep you within about half a degree of level with the center green light lit, based on my empirical measurements. But because the new level gauge is located more than four feet to the left and about six feet behind the center of the tank, if the coach is not level the gauge will probably be off. Tilted down toward the rear left at the limit of the green light deadband will cause a worst case of about 1/4 tankful too high. The opposite error would occur with the coach tilted diagonal toward the front right. For all other cases the error will be less. For instance, tilted toward the rear right or front left will cause the errors to largely cancel out. However, on average you should get within about ten percent of the true level. If you level your coach using bubble levels instead of the Power Gear idiot light, your accuracy can be much greater.