Water on petrol tank

Hi, it's that time of the year when I am preparing my Searay 185 to go to her summer mooring but noticed a little problem. The petrol tank sender unit is situated on top of the tank which is just under the deck in front of the engine, accessible via a sealed circular screw threaded plastic plate. However, when I went to change the sender unit as the gauge is not working I have noticed a reasonable amount of water on top of the tank covering the sender unit and it's connections. Rust has appeared on the metal of the sender unit and I assume that water should not get to that location. Can anyone advise if this has happened to them, where the water can be coming from and suggest any remedies

Re: Water on petrol tank

Doherto said:

Hi, it's that time of the year when I am preparing my Searay 185 to go to her summer mooring but noticed a little problem. The petrol tank sender unit is situated on top of the tank which is just under the deck in front of the engine, accessible via a sealed circular screw threaded plastic plate. However, when I went to change the sender unit as the gauge is not working I have noticed a reasonable amount of water on top of the tank covering the sender unit and it's connections. Rust has appeared on the metal of the sender unit and I assume that water should not get to that location. Can anyone advise if this has happened to them, where the water can be coming from and suggest any remedies

Click to expand...

Ayuh,... Welcome Aboard,... It's a Boat,...
Expect water to find it's way, EVERYWHERE....

The Cure, is to make sure everywhere in the hull, Drains to the pumpable bilge...

Re: Water on petrol tank

The top of my fuel tank is slightly concave, and water settles right on top of the sender. I think it's condensation from a damp bilge.

The wires were connected to terminals on the sender, which was under water. The connections were corroded.

I replaced the sender with a higher quality stainless steel unit, with long wires coming from the unit, so that you make the actual connection 2 feet away from the sender. I connected the wires with waterproof heat-shrink connectors, and coated the connections with liquid tape. Then I set the connections on a chunk of foam glued to the top of the tank, to lift the connections out of the puddle area.

I got a Wema sender: http://www.wemausa.com/tank-sensors/index.html#Fuel_Water_Tank_Sensors

I cleaned the sending unit top,and the tank around the sending unit with acetone, and smeared some 3m4200 sealant around the sender/tank seam, just to be sure no water could seep into the tank.

I haven't had any problems since.

Some people make a 'tent' with a sheet of plastic over the sending unit, so any condensing water collects on the plastic, and runs down past the tank. I haven't bothered doing this.

Also, make sure your round access hatch is sealed real tight. You might need a new hatch, or new hatch gasket.

Re: Water on petrol tank

jdlough said:

The top of my fuel tank is slightly concave, and water settles right on top of the sender. I think it's condensation from a damp bilge.

The wires were connected to terminals on the sender, which was under water. The connections were corroded.

I replaced the sender with a higher quality stainless steel unit, with long wires coming from the unit, so that you make the actual connection 2 feet away from the sender. I connection the wires with waterproof heat-shrink connectors, and coated the connections with liquid tape. Then I set the connections on a chunk of foam glued to the top of the tank, to lift the connections out of the puddle area.

I got a Wema sender: http://www.wemausa.com/tank-sensors/index.html#Fuel_Water_Tank_Sensors

I cleaned the sending unit top,and the tank around the sending unit with acetone, and smeared some 3m4200 sealant around the sender/tank seam, just to be sure no water could seep into the tank.

I haven't had any problems since.

Some people make a 'tent' with a sheet of plastic over the sending unit, so any condensing water collects on the plastic, and runs down past the tank. I haven't bothered doing this.

Also, make sure your round access hatch is sealed real tight. You might need a new hatch, or new hatch gasket.

Click to expand...

Jdlough, thanks for your reply and link, with your help also Bondo, I now know it is not a problem and I have a solution, great forum !!!

Re: Water on petrol tank

9 times out of 10 water sitting on top of the fuel tank is the deck plate leaking. When was the last time the entire assembly was removed and resealed? When was he last time the o-ring in the access cover was replaced?