False positive reading on Grey Tank sensor -- any ideas?

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False positive reading on Grey Tank sensor -- any ideas?

July 14, 2021, 01:00:05 pm

Hi folks,

So I understand how one could get a false negative reading on a tank sensor, if debris or something interfereds with the sensor itself, it might show the tank as more full than it actually is.

But on this trip we've noticed the opposite situation. Our grey tank sensor is always reading "empty" (green light on the lowest level of the readout display). Even when the tank is clearly more full than that. As a result, we have no indication of how full our grey tank is getting.

I know it's not as critical as the black tank, and we empty them at the same time. But still, I'd like to know if anyone else has seen this problem, and might know what causes it, and what, if anything, can be done to fix the problem?

Thanks in advance for all the wisdom in this group. It is always appreciated!

Re: False positive reading on Grey Tank sensor -- any ideas?

Reply #1 – July 14, 2021, 01:15:39 pm

The tanks have a series of screws bolted in at respective levels in the tank with wires attached as sensors. Likely a wire has broken off the solder tab, and most likely the ground lead. Check underneath - they can be resoldered, though take care to not melt the plastic of the tank.

Steve

Re: False positive reading on Grey Tank sensor -- any ideas?

Reply #2 – July 14, 2021, 01:36:25 pm

"The tanks have a series of screws bolted in at respective levels in the tank..."

Agreed, it's possible there is such a wiring problem! Should be an easy fix.

However, if the problem is not the wires to the sensors then perhaps a temporary solution would be Happy Camper.

The permanent solution is to install the SeeLevel system. With that system the sensors are on the outside of the tank and cannot be fouled. And, instead of three sensors, indicating levels of quarter, half and full, you get a linear readout as percentage of full. Much more accurate than the one you have now.

Re: False positive reading on Grey Tank sensor -- any ideas?

Reply #3 – July 14, 2021, 03:54:28 pm

Quote from: Steve - July 14, 2021, 01:15:39 pm

The tanks have a series of screws bolted in at respective levels in the tank with wires attached as sensors. Likely a wire has broken off the solder tab, and most likely the ground lead. Check underneath - they can be resoldered, though take care to not melt the plastic of the tank.

Steve

Thanks Steve, I'll see if I can find a loose or broken solder joint.

But this is a 2nd (actually 3rd-hand) unit, and the original owner had the tanks insulated (I assume by the LD factory).

Do you know if that makes it impossible to trace the wiring?

Re: False positive reading on Grey Tank sensor -- any ideas?

Reply #4 – July 14, 2021, 04:36:51 pm

Insulated tanks serve no purpose unless they can be heated. The insulation will just keep frozen tanks and valves unusable that much longer. If you can remove the insulation non-destructively, I would do so. Else get and install a Seelevel system, cutting away enough insulation to mount the strips.

Steve

Re: False positive reading on Grey Tank sensor -- any ideas?

Reply #5 – July 14, 2021, 04:47:58 pm

Your LD’s tank sensors may be coated with debris that prevents the connection
Our rig is now sitting in the driveway going through its annual septic tank enzymes soak. The holding tanks are freshly flushed and refilled with fresh water, along with a dose of septic tank enzymes in each tank.
https://www.homedepot.com/p/RID-X-9-8-oz-Powder-Septic-Tank-Treatment-19200-80306/202967489#overlay

This gets done every summer when it is hot and the rig is going to be sitting for a couple weeks. The enzymes eat the residual coating that lines both tanks, mostly comprised of grease.
After sitting, the tanks are drained and flushed again, removing the digested contents. This helps maintain the tank’s capacities and keeps the intank sensors clean. After 18 years, all the tanks' sensors still work fine.

Larry

Re: False positive reading on Grey Tank sensor -- any ideas?

Reply #6 – July 19, 2021, 12:08:42 am

Quote from: Larry W - July 14, 2021, 04:47:58 pm

Your LD’s tank sensors may be coated with debris that prevents the connection
Our rig is now sitting in the driveway going through its annual septic tank enzymes soak. The holding tanks are freshly flushed and refilled with fresh water, along with a dose of septic tank enzymes in each tank.
https://www.homedepot.com/p/RID-X-9-8-oz-Powder-Septic-Tank-Treatment-19200-80306/202967489#overlay

This gets done every summer when it is hot and the rig is going to be sitting for a couple weeks. The enzymes eat the residual coating that lines both tanks, mostly comprised of grease.
After sitting, the tanks are drained and flushed again, removing the digested contents. This helps maintain the tank’s capacities and keeps the intank sensors clean. After 18 years, all the tanks' sensors still work fine.

Larry

Thanks Larry, I think we will give that a try when we get back to NH for the rest of the summer. Can't hurt! Appreciate your experience and advice.

Re: False positive reading on Grey Tank sensor -- any ideas?

Reply #7 – July 19, 2021, 11:38:00 am

We basically ignore the gray and black tank sensors. In our use the critical factor is water. Our rate of water consumption is very consistent day to day. When the water is gone the tanks are ready for a dump (gray just short of full and black well short) and we simply go dump and fill water and we're done. In our case that's every four days.

LD did a pretty good job of equating water tank capacity and gray and black tank capacities. In our Rear Bath the water is 60 gallons and the gray 35 and the black 24. That apparently works out pretty close to our use. By the time we've used, say, 55 gallons of water, somewhat under 35 gallons have gone into the gray tank and less than 24 into the black. Provided we dump and fill at the same time this seems to take care of things. No need to sweat what the sensors are reading.

And we always travel with empty tanks and full water if possible. You never know for sure what the situation at your destination will be. We also find that when traveling (we tend to travel more than sit) that four days is a pretty good length of stay at most places. Enough time to explore and enjoy but not so long as to get bored.

Re: False positive reading on Grey Tank sensor -- any ideas?

Reply #8 – July 19, 2021, 11:52:48 am

Quote from: Terry Burnes - July 19, 2021, 11:38:00 am

We basically ignore the gray and black tank sensors. In our use the critical factor is water. Our rate of water consumption is very consistent day to day. When the water is gone the tanks are ready for a dump (gray just short of full and black well short) and we simply go dump and fill water and we're done. In our case that's every four days.

LD did a pretty good job of equating water tank capacity and gray and black tank capacities. In our Rear Bath the water is 60 gallons and the gray 35 and the black 24. That apparently works out pretty close to our use. By the time we've used, say, 55 gallons of water, somewhat under 35 gallons have gone into the gray tank and less than 24 into the black. Provided we dump and fill at the same time this seems to take care of things. No need to sweat what the sensors are reading.

And we always travel with empty tanks and full water if possible. You never know for sure what the situation at your destination will be. We also find that when traveling (we tend to travel more than sit) that four days is a pretty good length of stay at most places. Enough time to explore and enjoy but not so long as to get bored.

While we don't ignore, we have found that this is our normal time also

Re: False positive reading on Grey Tank sensor -- any ideas?

Reply #9 – July 19, 2021, 12:01:33 pm

Quote from: Terry Burnes - July 19, 2021, 11:38:00 am

We basically ignore the gray and black tank sensors. In our use the critical factor is water. Our rate of water consumption is very consistent day to day. When the water is gone the tanks are ready for a dump (gray just short of full and black well short) and we simply go dump and fill water and we're done. In our case that's every four days.

In our 2003 23.5' FL, the holding tanks have greater capacity (rated 28 and 32 gallons) than the fresh water tank, we can add ten gallons or more before finally filling them. Our gray tank fills faster than the black, an added transfer pump moves water from the gray to black tank, allowing us to use all the holding tank's capacity, gaining an extra day before dumping.
I suspect the tanks are a bit bigger than their stated capacity.

Larry

Re: False positive reading on Grey Tank sensor -- any ideas?

Reply #10 – July 19, 2021, 01:14:17 pm

Terry's method has worked for us also. I find that our black tank is maybe 1/2 full on our 98~MB when our gray water tank is full and our fresh water is near empty. I think that it is the showers that put us over on the gray tank. I am wondering if any one here has added a valve and port to divert shower water from the gray tank? Under our LD there are two lines running into the gray water tank and one of them looks obviously from the shower and has great access. We did this previously with our itaska, we had made a exterior shower but it was seldom used so diversion was way more successful. Then the black Tank mostly becomes the limiting factor? We would love to extend out time when we reach that shangri-La camping spot!

   Karen~Liam
   98 ~ MB
   NinA

Re: False positive reading on Grey Tank sensor -- any ideas?

Reply #11 – July 19, 2021, 01:30:34 pm

"I suspect the tanks are a bit bigger than their stated capacity."
---
Your tanks might be larger than listed; mine in the TK are not.

Still annoyed after almost 18 years!

Re: False positive reading on Grey Tank sensor -- any ideas?

Reply #12 – July 19, 2021, 02:21:45 pm

Quote from: Karen & Liam - July 19, 2021, 01:14:17 pm

I find that our black tank is maybe 1/2 full on our 98~MB when our gray water tank is full and our fresh water is near empty. I think that it is the showers that put us over on the gray tank. I am wondering if any one here has added a valve and port to divert shower water from the gray tank?

On most or all LDs, the black tank is higher than the gray tank. With a valve connecting the two tanks, the black will flow into the gray tank, and eventually if too much is transferred, it will back up into the shower, a nasty indicator that you have screwed up.

Our LD has an added port on the gray tank that goes to a pump that is used to transfer fluid from the gray to the black tank. The output of the pump dumps into the holding tank's vent pipe which feeds directly into the black tank. Filling the black tank nearly full enhances the clearing of the tank when dumped.
Our LD has a SeeLevel tank monitor that shows with more precision, than the Factory LEDs, how full each tank is
Pics here.
Holding tank transfer pump | Flickr
SeeLevel tank monitor | Flickr

Larry

Re: False positive reading on Grey Tank sensor -- any ideas?

Reply #13 – July 19, 2021, 08:23:52 pm

Larry,

Nicely done project… but of course I have a few questions. Was it a particularly difficult task to add the pump? It’s a little hard to see the black tank vent pipe connection. Is it just a screw-in fitting? How often do you clean the in-line filter? What model pump did you use? Have you ever tried installing a gray-to-black tank pump on a MB?

Thanks,
- John

Edit: I just realized that your project notes appear when I click on the pics. Brass I/2 inch NPT X 1/2 inch barbed hose fitting epoxied into 1 1/2 Inch black water vent pipe answered one of my questions and Pump Flojet Quad answered another.

Re: False positive reading on Grey Tank sensor -- any ideas?

Reply #14 – July 19, 2021, 11:20:47 pm

Speaking of tank levels... yesterday I got an email from Subaru, saying that my car had told them (!) that its windshield washer fluid level was getting low. I thought this "tattletale car" incident was rather hilarious. It wasn't as if I couldn't see the amber warning light on the dash, after all. What next--"Your glove compartment is too full. Please remove some items."?

Re: False positive reading on Grey Tank sensor -- any ideas?

Reply #15 – July 20, 2021, 10:17:50 am

Quote from: Andy Baird - July 19, 2021, 11:20:47 pm

Speaking of tank levels... yesterday I got an email from Subaru, saying that my car had told them (!) that its windshield washer fluid level was getting low. I thought this "tattletale car" incident was rather hilarious. It wasn't as if I couldn't see the amber warning light on the dash, after all. What next--"Your glove compartment is too full. Please remove some items."?

That is frightening. Can't you shut that spyware off?

Chris

Re: False positive reading on Grey Tank sensor -- any ideas?

Reply #16 – July 20, 2021, 01:05:19 pm

Quote from: Chris Horst - July 20, 2021, 10:17:50 am

That is frightening. Can't you shut that spyware off?

Many new cars are web-enabled and report to the manufacturer occasionally, in return, the manufacturer can upgrade the entertainment system remotely. Not sure if the engine's computer can update over the air, it's would seem to be too much of a security risk, giving hackers easy access to a car's maser computer, the ECM
I receive often notices that our Jeep's tires need air, the tires were riding too hard so the pressure was reduced from 37-psi to 32-psi. It also reports on the oil condition and who knows what else.
Not sure if the monitoring can be turned off, there is nothing in the owner's manual pertaining to it.
It's a brave new world. Big brother IS watching.

Larry

Re: False positive reading on Grey Tank sensor -- any ideas?

Reply #17 – July 20, 2021, 03:55:48 pm

"Can't you shut that spyware off?"

Dunno. I'll have to dig into the manual, but I've been busy lately. You're right, it is spyware, and I ought to take it more seriously.

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