3560 - holding tank level indicating sensor

General repair/maintenance/upgrade information exchange.

3560 - holding tank level indicating sensor

Postby ImRich » Mon Jun 19, 2017 10:05 am

On my 2005 3560 I always thought that the holding tank level gauge acted a bit strange.

As the boat was used, and the tank was being slowly filled, the gauge always seemed to not move at all, until the tank was almost full, then the gauge would suddenly seem to move from empty to full. So I learned early that the holding tank was not linear at all, and as soon as it starts to register a rising tank level, I knew I had to start making plans to empty the tank.

My boat is on a fresh water lake, so that the grey water from the shower sump has been rerouted to go into the holding tank instead of overboard. This means that EVERY drop of water that goes down every sink, the head, the shower drain and also the condensate from the air-conditioner ends up in the holding tank, so it can sometimes seem to fill quickly, especially if the weather has been humid.

This year it seemed even more erratic, so I decided to take on the smelly job of checking on the level indicator in the tank.

I didn't take any photos, but what I found was interesting, and confirmed why the holding tank level sender seemed to only indicate when the tank was almost full.

The Wema level sender itself is only about 4 inches long. So this means from empty to full, it will register only in the last 4 inches from the top of the tank as the tank itself seems to be about 8 inches deep.

I believe that this is the sender:
http://www.wemausa.com/sensors/level-HoldingTank.shtml

My guess is that the sender is designed to be shorter than the full depth of the tank so as to keep the sender away of the bottom of the tank to keep it out of the "sludge" at the bottom of the tank to help keeping it from being fouled from the heavier semi-solids at the bottom of the tank.

The float was still working well. It's contained inside of a stainless steel cage or shell, which contains small holes to allow fluid in, but to keep solids out. There was a clip on the bottom that allowed me to remove the stainless shell and gain access to the inside and the sliding float. I cleaned the device as best I could. It looks well designed in that it should be difficult for it to get "gummed up".

But at least now I understand that the gauge as designed and installed won't show the tank from empty to full in any type of linear fashion. Indeed, once the level start registering on the gauge, the tank is about half full, and you're only reading the second half of the tank fill level.

Here is a link to another online article that someone else wrote up on how to clean these:
http://www.lifeonthehook.com/tag/cleani ... nk-sensor/

It was a smelly job, done with gloves on, but easy to check and confirm that the gauge was still functioning properly.
Last edited by ImRich on Thu Jun 22, 2017 7:49 am, edited 1 time in total.
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Re: 3560 - holding tank level indicating gauge

Postby gofast24 » Mon Jun 19, 2017 10:53 am

Yes, doing anything with the black water tank is smelly/messy! Why did you re route your grey water drains to the black water tank? On our vessel the black water tank gauge is fairly linear from 1/4 full to 4/4 full. The sender/gauge is about the only thing we have not had a problem with yet, knock on wood! At least you now know what your gauge is reading vs. the actual fill level in the tank. Last year we put in a new fwd sump pump, with the new super reliable electronic liquid level switch (Johnson 12V 1000 GPH multi port sump pump with electronic switch). It Has stopped pumping 3 times to date since installing. The electronic level switch doesn't like soap scum from either the shower, fwd head sink, or galley sink! It does like AC condensate water so that is great? What else can you use it for other than water that has been used with soap in it (Or the AC condensate) ? Time to go back to the old style "float" switch that always worked other then when the inlet screen gets plugged but then all you have to do is flush the screen and back working again!
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Re: 3560 - holding tank level indicating sensor

Postby ImRich » Thu Jun 22, 2017 7:58 am

On our lake, they route all grey water to the holding tank, or put in a separate grey water tank. They don't allow any grey water overboard, it all must be pumped out. I didn't do the work, it was done by the first owner when the boat was first brought to the lake.

Link to the state's DES page on this:
https://www.des.nh.gov/organization/div ... charge.htm

Here's a document that shows what they inspect:
https://www.des.nh.gov/organization/com ... /bb-38.pdf

My guess is that the grey water was originally routed to the shower sump, which then went overboard. Then they routed the shower sump to the holding tank, it probably was an easy job for the marina at the time.

I'd like to reroute the air conditioner condensate overboard, as that is after all just distilled water. It's amazing how fast the holding tank can fill from this over the course of a week if the weather is humid. Before I realized this, I used to wonder how my GF could fill the holding tank so quickly!! LOL

My problem is that on the 3560 there isn't a lot of spare room for another shower sump to allow me to route the A/C condensate drain. I don't want to chance using one of the venturi condensate devices that are available, because if that fails, the boat would fill with water by the A/C pump.

If I could get at the side of my holding tank, I'd install one of the exterior type of tank level monitors, but that's not an easy option as I can't access the side of the tank on the 3560 without major surgery.

I was also considering one of the newer (non float) type of level senders, but now that I cleaned what I have, I'll see if it's more reliable. I was simply surprised to find that it only reads the fill level of the top half or 1/3 of the holding tank. Understanding how it works goes a long way.
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Re: 3560 - holding tank level indicating sensor

Postby gofast24 » Thu Jun 22, 2017 12:00 pm

Not sure why grey water would be detrimental to a lake, just fresh water with some dish or bar soap in it but if that is what your NH DNR requires not much you can do about it? I am still unhappy about the "electronic" float switch in our 3 rd new fwd. sump pump, it is constantly malfunctioning, especially when not using the shower/fwd head sink or galley sink, just fwd. AC condensate water which backs up into the pan under the AC, stays full of water, and will eventually rust out the pan and require a new pan (have to completely remove the AC unit to do it!)
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Re: 3560 - holding tank level indicating sensor

Postby ImRich » Sat Jun 24, 2017 7:18 am

A neighbor got me thinking, I'm wondering if my level sensor was ever replaced, and they used one that was too short for the tank? Perhaps this is why it only shows the top half of the tank level?
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Re: 3560 - holding tank level indicating sensor

Postby gofast24 » Sat Jun 24, 2017 10:54 am

ImRich wrote:A neighbor got me thinking, I'm wondering if my level sensor was ever replaced, and they used one that was too short for the tank? Perhaps this is why it only shows the top half of the tank level?

Our sender on the black water tank fully extends to within about a inch of the bottom so we get good accurate reading from about 1/8th full to full full! Sounds like your analysis of the sender being replaced with a too short unit is what you may have? It's up to you to replace it with a proper length sender if you want any accurate readings before it is more than 1/2 or 3/4 full? Not knowing how full it is before sailing can be a PITA especially when you just anchor and find out your black water tank is almost full and you cant empty it while at sea.
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Re: 3560 - holding tank level indicating sensor

Postby rlynch03 » Sat Jun 24, 2017 8:26 pm

We have a similar issue in our 3760, the sender is very short and doesn't read until it is almost full. However we have learned to pump out each week anyway.

I would prefer for it to read correctly.

ImRich let us know if do replace the sender and what you go with.
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Re: 3560 - holding tank level indicating sensor

Postby gofast24 » Fri Jun 30, 2017 10:46 am

IMRich, suggest you measure the "depth" of your tank from the sender's mounting surface on the top of the tank to the bottom of the tank and replace the 4" sender with one that is 1" or so shorter than the the total depth of the tank. you should get much more accurate reading on the tank's fill level doing this?
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Re: 3560 - holding tank level indicating sensor

Postby ImRich » Sat Jul 01, 2017 6:13 am

Yes, I may replace it with one of the correct length.
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Re: 3560 - holding tank level indicating sensor

Postby timp4411 » Mon Jun 11, 2018 11:09 am

Rich,

I know it's an older post.... but did you ever replace the sensor?

I'm contemplating replacing mine on my 3860, but not real enthused about that particular job.

Thanks.
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Re: 3560 - holding tank level indicating sensor

Postby ImRich » Mon Jun 11, 2018 3:53 pm

No, I never replaced it.

I did take it out, cleaned and tested it and it seems to work, and at the time, I put it back together.

Obviously, It's not a fun job, but not too bad if you do it when there is a breeze around to help clear out the smell from the cabin, and use rubber gloves, protect your carpet from drips, etc.

I may still replace these someday, but I haven't chosen which type of sensor to use. If I do replace it, i'd like it to be something that is more reliable, less prone to cloging, and more accurate.
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Re: 3560 - holding tank level indicating sensor

Postby timp4411 » Tue Jun 12, 2018 8:43 am

Thanks for the info Rich.

I may try to remove the sensor and clean if that worked for you.

I have priced out a brand new sensor and it's going to run $100.

It's worth it to try a cleaning first.

Happy Boating !
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Re: 3560 - holding tank level indicating sensor

Postby kellyg » Tue Jun 12, 2018 8:59 am

I have the same sensor, and clean it every 2 years. I've had the boat for 17 years without a problem.
Add quick connects on the wires to make the job easier the next time.
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Re: 3560 - holding tank level indicating sensor

Postby timp4411 » Wed Jun 13, 2018 11:18 am

kellyg wrote:I have the same sensor, and clean it every 2 years. I've had the boat for 17 years without a problem.
Add quick connects on the wires to make the job easier the next time.


Thanks for the tip.

I have been replacing just about all my connections with the pin and socket quick connects in areas where they won't get a ton of moisture.
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