Water tank sender unit.

[bammylovechops]

Hello,
I was fed up with my water tank gauge never being accurate so I decided to try to fix it. I thought it would just be a simple case of replacing the tank sender unit. I cut the new sender probe to length
( thanks to Nick at Seabridge), installed in the tank and it is still not reading accurately, I also removed the resistor in the gauge that shows the water level in the tank as per the recommendation in the instructions that came with the probe.
The problem is I'm not actually any better off in getting a true ish guide to how much water I've got.
Other than now having to replace the gauge in the dashboard, and I still don't know if that is the fault!
Any thoughts appreciated.
The boat is a Sealine F34 2006.
Mark

 

[jimmy_the_builder]

In what sense is it inaccurate? ie too low, too high, or lagged, or all over the place? If you've cut the sender down, what resistance readings is it showing at full and empty?

 

[bammylovechops]

In what sense is it inaccurate? ie too low, too high, or lagged, or all over the place? If you've cut the sender down, what resistance readings is it showing at full and empty?

Hi,
Sorry for delay in reply.
I can either adjust it to show full, when it is actually full, but then when the tank runs dry the gauge shows about a quarter, or adjust it to show empty when it is actually empty, fill the tank via a hose pipe but with the tank overflowing it only shows under three quarters, it's as if the difference between the two isn't enough, if that makes sense ������

 

[jimmy_the_builder]

Hi,
Sorry for delay in reply.
I can either adjust it to show full, when it is actually full, but then when the tank runs dry the gauge shows about a quarter, or adjust it to show empty when it is actually empty, fill the tank via a hose pipe but with the tank overflowing it only shows under three quarters, it's as if the difference between the two isn't enough, if that makes sense

Sounds like your sender is returning different resistance readings to those expected by the gauge, which makes complete sense given that you've cut the sender down - hence my question about resistance readings. When one of my senders failed, I had one made by Wema that was exactly the right length for my tank, so I got the correct resistance readings at full and empty. Iirc there are basically two sender resistance schemes, something like 0-180 ohms and 220-40 ohms, for EU and US boats (I could be completely wrong on this, so dyor sorry - this was all years ago). I'd suggest you either need a custom-made sender for your tank so your gauge gets the correct resistance readings, or you need a cleverer gauge that can copy with the non-standard resistances of your cut-down sender. From memory, my custom sender from Wema was about £110.

 

[bluetooth]

Sounds like your sender is returning different resistance readings to those expected by the gauge, which makes complete sense given that you've cut the sender down - hence my question about resistance readings. When one of my senders failed, I had one made by Wema that was exactly the right length for my tank, so I got the correct resistance readings at full and empty. Iirc there are basically two sender resistance schemes, something like 0-180 ohms and 220-40 ohms, for EU and US boats (I could be completely wrong on this, so dyor sorry - this was all years ago). I'd suggest you either need a custom-made sender for your tank so your gauge gets the correct resistance readings, or you need a cleverer gauge that can copy with the non-standard resistances of your cut-down sender. From memory, my custom sender from Wema was about £110.

Jimmy
The water guage/sender on my 2002 T40 isn't working and seems stuck at 1/4 full despite filling/draining water tank. I have removed sender unit and played around with it with someone looking at the gauge and it moves if I reverse the wires so presume its the sender at fault. Interested to know what you did specifically to get a customised the sender; was it just a internal height calculation of tank? Is it a standard type for Fairlines ? Or did you end up buying new gauge as well?
Have seen page - http://www.wema.co.uk/pg_fuel_and_water.htm

Any advice appreciated.

 

[jimmy_the_builder]

Jimmy
The water guage/sender on my 2002 T40 isn't working and seems stuck at 1/4 full despite filling/draining water tank. I have removed sender unit and played around with it with someone looking at the gauge and it moves if I reverse the wires so presume its the sender at fault. Interested to know what you did specifically to get a customised the sender; was it just a internal height calculation of tank? Is it a standard type for Fairlines ? Or did you end up buying new gauge as well?
Have seen page - http://www.wema.co.uk/pg_fuel_and_water.htm

Any advice appreciated.

Take the sender out and check the resistance as you move the float up and down the rod, you'll quickly see if it is not working correctly. To order a custom-made sender from Wema you just need to know what length sender you need - and that's obviously just the same as the sender you have now. That's all I had to do, didn't need to change any gauges.

 

[bluetooth]

Take the sender out and check the resistance as you move the float up and down the rod, you'll quickly see if it is not working correctly. To order a custom-made sender from Wema you just need to know what length sender you need - and that's obviously just the same as the sender you have now. That's all I had to do, didn't need to change any gauges.

Many thanks Jimmy - will approach Wema
Simon

 

[jimmy_the_builder]

Many thanks Jimmy - will approach Wema
Simon

Prompted by this, I've dug out the emails with Wema. Cost was £86 in 2013, and it turns out the sender resistance range was 0-190 ohms, and they were produced specifically for Fairline. Contact email address is info@wema.co.uk. Good luck!

 

[Nick_H]

Jimmy
The water guage/sender on my 2002 T40 isn't working and seems stuck at 1/4 full despite filling/draining water tank. I have removed sender unit and played around with it with someone looking at the gauge and it moves if I reverse the wires so presume its the sender at fault. Interested to know what you did specifically to get a customised the sender; was it just a internal height calculation of tank? Is it a standard type for Fairlines ? Or did you end up buying new gauge as well?
Have seen page - http://www.wema.co.uk/pg_fuel_and_water.htm

Any advice appreciated.

Bluetooth, have you checked whether the gauge works when you remove it and slide the float up and down manually, without swapping the wires? The reason I ask is that my sender periodically jams every couple of years. I remove it and it looks perfectly clean and free to move, but if I just put it back in the tank then it jams again. However, if I give it a good clean with soapy water then it works fine again.

It seems there must be some invisible algae growth or something which causes the float to stick.

 

[bluetooth]

Bluetooth, have you checked whether the gauge works when you remove it and slide the float up and down manually, without swapping the wires? The reason I ask is that my sender periodically jams every couple of years. I remove it and it looks perfectly clean and free to move, but if I just put it back in the tank then it jams again. However, if I give it a good clean with soapy water then it works fine again.

It seems there must be some invisible algae growth or something which causes the float to stick.

Cheers Nick
I will check that again
Simon

 

[bluetooth]

Well had some spare time today and found that Nick_H's advice worked a treat (warm water/fairy liquid).
Many thanks
Simon

 

[bluetooth]

Well only taken a few years to fully sort!
The gauge never worked properly despite cleaning.

After chatting to Stuart Bateman at Wema UK who was very helpful I bought this replacement sender unit:
Fuel & Water Sender - S3 (screw fit)

The webpage blurb explains the improvement in design and accuracy of the new senders.

Is 45cm replacing the factory fit 40cm. I measured water tank on Targa 40 to be 46.5cm deep so should be very accurate now.
Fitted and tested today and fully functional with previous gauge.

Im very pleased have actually got round to it now !
Simon

 

[Bouba]

Sender units can get calcified from water, a quick clean with a décalcifier can make it work again