MS 30 Pilot II waste tank sender/gauge

It appears that my waste tank gauge in the head has suddenly decided to no longer display anything but empty. My tank is seldom used and kept quite pristine with frequent evacuation and lots of fresh water pumped through it. Without major surgery in the head, gaining access to the rear of the firmly mounted gauge to check out things at that end seems about impossible, and the Wema sender at the tank is only several inches below the cockpit deck making its removal impossible without cutting an access hole. I am quite ok with cutting a four-inch access hole and finishing it off with a nice white circular deck okate from West Marine, if I have to. I cut a 10X20 inch access to get to the Vacuflush vacuum generator several years back and have a nice looking deck plate there. My plan at this point is to see if I can get the spec from Wema for the ohm reading across the two wires removed from the current sensor (for a full tank, as mine currently is with clear freshwater). Assuming that checks bad, I will order a new sensor and before cutting the access, check the gauge by connecting the new sensor to the system and sliding the magnet up and down the rod to see what the gauge does. I went through this with both fuel tank sensors. Diving into the lazarette hatch head first I can get decent access to the sensor top to get my snake camera to it so I can write down the model number and to connect and disconnect its wiring.

I had a Vetus (I think) gauge & sender for my holding tank. The sender float mechanism was a constant headache and the thing only worked half the time, even after replacement. I think it might have been because my tank is mounted vertically and at a slight angle/offset (came that way from the factory). I ended up replacing it with an externally mounted level monitoring system by Gobius. I think it is some sort of ultra-sound technology. I have been very happy with this.
I think Gobius is a Swedish company, so may not be practical for you to consider...but perhaps the equivalent technology is offered by some company in the States??


https://www.gobius.se/en/products/


The picture below is not my tank, but rather, from the Gobius website.

I installed a SCAD tank monitoring system in my last boat to replace the troublesome mechanical one. I just left the old sensors there, this system mounts on the outside. 2 seasons with it, and it works great!

https://www.scadtech.com/tank_monitors

Someone here also has the link to the guy who invented the SCAD system, he used to sell them cheaper directly marketed under another name for a little less $.

rgano said:

It appears that my waste tank gauge in the head has suddenly decided to no longer display anything but empty.

Without major surgery in the head, gaining access to the rear of the firmly mounted gauge to check out things at that end seems about impossible, and the Wema sender at the tank is only several inches below the cockpit deck making its removal impossible without cutting an access hole. I am quite ok with cutting a four-inch access hole and finishing it off with a nice white circular deck okate from West Marine, if I have to.

Click to expand...

Rich, there is likely a 3A inline fuse on that circuit, so you could check that first.

I had to cut an access hole to replace our WEMA freshwater sender. Straightforward.

WEMA's new style screw-in holding tank sender is still sometimes subject to clogging. If the float is at it's lowest point, and clogged, the symptom will be that the gauge shows empty. Given decent access, it's very simple to unscrew the thing, clean it, put it back in, reconnect the electrics (I used spade-style disconnects).

I even graduated to having two senders, so if one eventually got clogged (seemed to be every 2-3 years or so) I just took it out, put the other in, cleaned the clogged on at my leisure.

-Chris

Rich, dumb question, does the gauge move if you fill the tank with water?

mncruiser said:

I installed a SCAD tank monitoring system in my last boat to replace the troublesome mechanical one. I just left the old sensors there, this system mounts on the outside. 2 seasons with it, and it works great!

https://www.scadtech.com/tank_monitors

Someone here also has the link to the guy who invented the SCAD system, he used to sell them cheaper directly marketed under another name for a little less $.

Click to expand...

I bought the SCAD style unit from Ferrielo Sales, who was the oem, but it appears that they are no longer in business. His website is dead, and searching for the SCAD Solo unit, it lists as discontinued. They do have a new unit, TM1, which uses the same external sensors. My unit has worked well for 3.5 years, and I also let the old sensor in place.

Good luck,
Brett

There's nothing wrong with your gauge, Rich...the animal fats in waste have built up on and clogged the senders in the tank. It's a common problem for owners of WEMA, Dometic/SeaLand TankWatch systems and all others that use senders INSIDE the tank. It typically takes about two years for the buildup reach the point of preventing the senders from reading the level in the tank....and there's only one cure: remove the sending unit to clean the probes by hand with a brush in a strong solution of detergent and water.


There are several companies who make systems that use senders that go on the outside of the tank. The Profile System from Ferriello Sales and sold by SCAD under their private label brand name, which was top rated by Practical Sailor, ceased production with Dennis Ferriello's death about 6 months ago. SCAD still offers tech support and replacement parts (see "Legacy Tank Monitors" in the menu on the left side of page on the SCAD site), but now offers TM Tank Monitors, which are state of the art and what I now recommend Scad Tank Monitors.

--Peggie

Update

This morning I emptied and refilled the tank using the deck pump-out fitting and the macerator pump. Flipped the "Head" circuit breaker for the Vacuflush, and the gauge read 3/4 full. Yesterday, it remained lighted (as it always does when the breaker is on), but the needle stayed at empty when I filled the tank. SOOO, when I energized the breaker for the macerator pump, the needle immediately jumped to empty and then returned to somewhere between 1/2 and 3/4 full when I stopped the pump. Some version of this behavior repeated itself again, and then the needle went to zero from somewhere less than 1/2 and stayed there as the level was decreased back to zero.

Then I cut the wires at the sensor where it exits the tank and took resistance readings at both empty and full again - 242 Ohms. The sensor is a Wema S3U-8 and is supposed to read zero empty and 180 Ohms full.

A new 62-dollar sensor is on order from KUS/WEMA, and I will make a temporary connection to it and slide the float up and down it to view the action of the gauge before I cut the 4-inch access in the deck needed to retract the old one and insert the new. If the gauge proves faulty, there will be no need to cut the access because I will shift to some external measuring system or just start opening the laz hatch to see the level from now on.

I have recent experience with the newest version of the SCAD system, installed in the boat earlier this year, and I have to say I like the type needle gauge I have better than the sequential LEDs of the SCAD and its complex setup. Sure hope my gauge checks out OK cuz I am not gonna destroy the head to get it out.

Get RV Digestit. You can get it at Amazon or at an RV store. Dump the entire bottle into the tank and fill the tank 80% with water. Go for a ride and let it work around. Let it sit for two days or so. It shoule disolve any gunk on the sender unit. I use it in every tank after pumpout.

rgano said:

Then I cut the wires at the sensor where it exits the tank and took resistance readings at both empty and full again - 242 Ohms. The sensor is a Wema S3U-8 and is supposed to read zero empty and 180 Ohms full.

Click to expand...

From memory, I'd have expected that to be a 33-240 Ohm (Full-Empty) sender... but then again my memory has flaws...



-Chris

You might check the ground wire to the sensor.
Dennis

My tank is as clean as a whistle, and I use Noflex in it; so I am pretty sure my senor's float is not stuck. I will find out when I remove it before I install the new one.

Assuming the float is buoyant and moving along the shaft OK, the resistance readings across the two wires right at the top of the tank are 242 Ohms regardless of the level of the water in the tank. It is supposed to be ZERO at empty and 180 Ohms at full. I am confident the issue is with the sensor, just like it was with my fuel tanks.

I will let you all know what happens with this. Not sure when the new sensor will arrive.

New S3U-8 tank level sender arrived from KUS today, and it turned out there was enough clearance over the waste tank on this boat to remove the old and insert the new. So big ugly access hole averted. Yesss! Here is a photo of the removed sender as it came out with no cleaning whatsoever. The slider was moving quite freely. I told you my tank is clean as a whistle. Gauge works just fine just as Peggy said it would, and all is happy in Richville.

Now to keep the three children we are hosting on the boat Friday from pooping in my nice clean tank.

Looks like an older sender. Our updated replacements have the metal float captured inside a perforated tube, and the new tube looks larger in diameter...

-Chris

I agree, but to ensure it all fit back together with correct threads etc, I ordered the original part number. I am not so sure I would want something overly complex and full of spaces to get clogged up in there anyway. Sometimes progress isn't.

I haven't had to replace any of my sensors but I understand Wema / KUS has discontinued some models used by MS. I did find replacement / xRef #s on their website a few yrs ago.