How do water level sensors work? What to do when they don't? 17' Bigfoot. 1990. - Fiberglass RV


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Old 08-14-2017, 08:39 PM   #1
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Red face How do water level sensors work? What to do when they don't? 17' Bigfoot. 1990.

My fresh water tank was an algae pool. I cleaned it and replaced all the hoses with nice new ones and made solid connections.

Before starting the project I noticed the lights on the acculevel were working (more or less - they never recognized when the tank was totally full). I thought that cleaning it all would make it work better.

In fact it's gotten worse. The level lights don't register 1/4 full until it's about 3/4 full and then once almost topped off it reads 1/2 full. Never more.

I put the wires all back exactly where they were. I also sanded the rust off the washers. But I don't think that matters much. The bolts are stainless, clearly.

My guess is these sensors work by some kind of continuity principle. But I really don't know.

Can someone here explain exactly how these sensors work and what to do to get them to work correctly?

NOTE: all wires are back where they started. And when I started they did work in order as the tank filled up. So it's gotten worse, not better.

Thanks for your help.
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Old 08-14-2017, 11:03 PM   #2
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I dont know the particulars of your "acculevel" but tank probes all work basically on the same principle. When a probe comes into contact with liquid on the inside of the tank, there is conductivity and that probe sends an electrical signal to the monitor. If you're getting false or inaccurate readings even after cleaning the probes, the best solution would probably be to swap them out with new ones. They are pretty inexpensive (at least the simple stock ones are). Also, check the probe wires for any breaks or corrosion. If there is any, consider replacing the probe wires as well.
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Old 08-15-2017, 09:43 AM   #3
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Thanks rbryan.

The probe, in my case, seems to be a stainless screw and not much more. The screw goes through a rubber grommet and holds the wire down. There's a washer as well. I cleaned everything. The screws were clean untarnished to begin with.

So is the screw the probe? I assume so. The tip of the stainless screw sticks into the water through the grommet.

I agree there could be a problem with the wires. I can check their continuity.

Still, it's strange that more seems to be going wrong after cleaning than before.

Replacing the probes seems like just replacing a screw, but the screws are fine. Am I missing something with the probes? I cannot see the inside of the tank where the probes are, but I assume the metal of the screw is the part that's touching the water and there's no mystery outside of that simple principle.
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Old 08-15-2017, 10:24 AM   #4
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You have the same exact system I have. Mine work perfectly, some times, and give false readings often. Flushing the tanks helps somewhat, but "unreliable" would be how I would describe the gages. On an individual basis, The fresh tank gauge is the most reliable and the black tank gauge the least reliable. I believe this is a common situation. Removing and replacing sensors, if you can find them, might cause more problems (leaks) and is likely to have little change in reliability.
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Old 08-15-2017, 10:36 AM   #5
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Jack, what exactly is a sensor in this case? Is it simply the bolt sticking into the tank? As far as you know are there any moving parts we cannot see?

As I see it, replacing the sensor means replacing a stainless steel bolt. But a bolt is a just a bolt. It's doing its job of conducting.

I can easily live with this situation. I always take a look at the tank from time to time. I'm just curious and I like things to work as they should.
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Old 08-15-2017, 10:53 AM   #6
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Thanks rbryan.

The probe, in my case, seems to be a stainless screw and not much more. The screw goes through a rubber grommet and holds the wire down. There's a washer as well. I cleaned everything. The screws were clean untarnished to begin with.

So is the screw the probe? I assume so. The tip of the stainless screw sticks into the water through the grommet.

I agree there could be a problem with the wires. I can check their continuity.

Still, it's strange that more seems to be going wrong after cleaning than before.

Replacing the probes seems like just replacing a screw, but the screws are fine. Am I missing something with the probes? I cannot see the inside of the tank where the probes are, but I assume the metal of the screw is the part that's touching the water and there's no mystery outside of that simple principle.
The sensor or probe is the bolt itself. If something sticks to it on the inside of the tank (unlikely in a fresh water tank but possible), the probe will conduct a small electrical current back to the monitor and register a false reading.

False readings or problems with the probes on a fresh water tank is a pretty rare thing, mainly because they only come into contact with fresh water. But considering how much algae build up you had inside the tank before cleaning it, there could be some build up that would affect the probes as well.

I'm assuming you removed the probes when you cleaned the tank and cleaned the inside part of the probes? If not, you can remove, clean and reinsert them pretty easily. But, I'd suspect the wires before anything else. They are pretty thin, and any breaks or corrosion will result in false readings as well.

By the way, here's a link to a video on how to pull the probes without damaging the tank. Pretty easy method using a washer and a wrench. The video was made by a guy who swapped out the stock bolt probes with Horst Probes (we have them on our trailer), but you could use the same method to just remove and clean the probes.

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Old 08-15-2017, 11:24 AM   #7
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The previous information is all correct. I want to stress the utter simplicity of these systems. Imagine a 5 gallon bucket under a leaky roof. You want to know when the bucket is full.

You simply have two electrical contacts in the bucket. When the water reaches them it closes a circuit and a buzzer buzzes, or in your case an LED is lit. Multiple contacts at different levels in your tank approximate 1/4, 1/2, 3/4, full.

In this case, the bucket is replaced by a water glass.
5 Minute Water Sensor (with Pictures)
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Old 08-15-2017, 11:33 AM   #8
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Does anyone have any first hand experience with positive results here? The video makes replacement look pretty simple but the sensors appear be something that would last forever. I would hate to risk a cracked tank, and find that the original sensors were still good.
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Old 08-15-2017, 11:49 AM   #9
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Thanks everyone.

I get it.

The replacement probes look good.

But before buying them, first it's time to check if the wires are loose somewhere. Now that I get the principle I'll get to testing everything and report back.
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Old 08-15-2017, 02:29 PM   #10
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Quote:
Originally Posted by Nik View Post
My fresh water tank was an algae pool. I cleaned it and replaced all the hoses with nice new ones and made solid connections.

Before starting the project I noticed the lights on the acculevel were working (more or less - they never recognized when the tank was totally full). I thought that cleaning it all would make it work better.

In fact it's gotten worse. The level lights don't register 1/4 full until it's about 3/4 full and then once almost topped off it reads 1/2 full. Never more.

I put the wires all back exactly where they were. I also sanded the rust off the washers. But I don't think that matters much. The bolts are stainless, clearly.

My guess is these sensors work by some kind of continuity principle. But I really don't know.

Can someone here explain exactly how these sensors work and what to do to get them to work correctly?

NOTE: all wires are back where they started. And when I started they did work in order as the tank filled up. So it's gotten worse, not better.

Thanks for your help.
:Nik it does not matter most of these gauge things never work right. The only one I know is pretty accurate is the one that was in my old gas tank on our Studebaker Pickup when it said empty it was, how do I know this because I was out of gas and had to hoof it to a service station. The ones in our MH they are not accurate like that one was but they do a pretty good job and I am Amazed. You would think with the Technology they have today in getting men to the moon they could figure out how to build better and more accurate gauges.
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Old 08-15-2017, 10:23 PM   #11
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Originally Posted by Nik View Post
Thanks everyone.

I get it.

The replacement probes look good.

But before buying them, first it's time to check if the wires are loose somewhere. Now that I get the principle I'll get to testing everything and report back.
Be aware that when it comes to the fresh water tank, the inexpensive stock probes are fine. The fancier (and much more expensive) Horst probes mentioned in the video I posted earlier are for the gray and black tanks. That's because these tanks are susceptible to more build up and are notorious for having probes get fouled up and produce false readings. The Horst probes are much more reliable there.

You're on the right track in checking all the electrical connections first.
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Old 08-16-2017, 06:11 AM   #12
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I've heard people mention they cut a hole in the top of the tank and installed a deck plate hatch to get access into the tank to thoroughly clean it.
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