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Old 08-04-2019, 11:52 AM   #1
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WEMA Water Sensor 242 Ohms at half Tank?

Hello,

This new to us 2006 Mainship has 2 75 Gallon water tanks and a WEMA dual Quanity Gauge. (1/2 switch) Gauge needle twitches when on Tank 1 and nothing on 2.

I gained access to the Port tank sensor, cut the wires and had 242 Ohms read (pink & black) and the tank is half full...not good,,..According to a WEMA troubleshooting guide I used, 232-252 ohms equals empty, which is what the gauge is showing....I am guessing the sensor is bad but both tanks at the same time?

Looking for advice....
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Old 08-04-2019, 11:56 AM   #2
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How far down into the tank does the tube extend? If the float is at the bottom of the tube, but the tube is several inches above the actual bottom of the tank... the float (242 Ohms) might think the tank is empty when it's not really.

I've had to calibrate WEMA gauges using an eyes-on approach, but mostly that's been about the holding tank and not so much the fresh water tanks...

-Chris
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Old 08-04-2019, 12:05 PM   #3
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That is true but I have no way of seeing how far it extends into the tank, best guess would be that all efforts were made to try to use a sensor that was the best fit goes as far as accuracy went....
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Old 08-04-2019, 12:38 PM   #4
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I had a "twitching" fuel gauge sensor. Same type - with float. Used a meter and saw random resistance readings while sitting still. New sensor solved the problem.
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Old 08-05-2019, 08:11 AM   #5
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Quote:
Originally Posted by jefndeb View Post
That is true but I have no way of seeing how far it extends into the tank, best guess would be that all efforts were made to try to use a sensor that was the best fit goes as far as accuracy went....
You would think. But if access was on a diagonal, they could also have wimped out and just inserted the tube the could get "around the corner" (so to speak) and it could have been shorter. If you can get a backlight on the tank, you might be able to get a visual on tube depth. Just a thought.

Our two water tanks are connected, fill one, draw from the other, so we only have a single fresh water sensor. And there's a 3-amp blade fuse in the circuit. I haven't seen a system with a 1/2 switch, but I wonder if each leg might have it's own fuse?

Also, WEMA (now KUS) switched from plastic tubes to stainless, sometime after at least 2003/2003. Would have thought that happened before your boat was built, but in any case, the plastic units failed a lot, and the stainless ones seem to last forever. (Well, at least 12 years so far...)

-Chris
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Old 08-05-2019, 08:15 AM   #6
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This what I think I have, if anybody happens to know the part/model number for these sensors, please pass it along...( i think they are mostly the same, just different lengths...)
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Old 08-05-2019, 09:51 AM   #7
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This might be it.
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Old 08-05-2019, 08:17 PM   #8
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OK, sure looks like it, I guess it just screws in to the plastic tank?

I will have to measure the depth in inches of the tank.

The other tank (Starboard) is almost impossible to reach so seeing they are connected together I am thinking fixing at least one will be good enough?
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