Mystery bilge water

Nmor830

Member
Sep 12, 2016
90
Channel Islands
Boat Info
2008 340 Sundancer
Engines
8.1l Mercruisers
340 Sundancer keeps getting about 2 inches of water in bilge. Can’t find the source? At dock, I’ve cleaned and dry the bilge and it will sit for days and stay dry. I’ve run the engines to see if there is raw water leaking somewhere and nothing. As soon as it’s run out on the water when I return the bilge has water. Again there is no noticeable areas of a leakage. I’m not sure how much it’s taking on because the pump might be draining some out. All the through fittings, vdrives look ok, don't show any signs of leaking?
Anyone run into this and have any suggestions? Really don’t want to pull out of the water unless absolutely necessary.
Thanks,
Nick
 
When you come off plane, any water making its way onto the swim platform?
 
Mine did that, and it was the cool fuel module barbed fittings.
 
I was going to suggest you take a look at your shafts to see if they're dripping. That wouldn't happen just sitting at the dock or with the engines running. It'll only happen if the shafts are turning. The water is to cool the shafts.

Please let us know what you find out.
 
Agree with above being most likely cause. Even if dripless they may leak underway. Try to get it fixed as the salt water will rot away the oil pans.
 
Look around your rudder shafts also. Sometimes hard to notice, may be a slight trickle as you turn the wheel.
 
All good suggestions and I have looked closely at all of them. Shaft seals are the first thing I checked and they are dry. There’s a channel that separates any water that would flow in that area with a drain hole toward the front. It’s completely dry. If the seals were leaking there would a little reside water remaining in the channel. Both sides are dry. Checked the cool fuel modules as well as raw water pumps but all seem to be very dry? Some mystery. I’ll keep searching and report when something is found.
Thanks, Nick
 
When you come off plane, any water making its way onto the swim platform?
I’m pretty cautious when slowing down and it’s a good thought. I didn’t notice any trace of excess water that would flow down the stern inside the bilge.
Thanks
 
O rings going bad on a transducer? I had a similar issue and traced it to a leaky transducer
 
While running check your exhaust. Mine had a pin hole in the stbd exhaust way back by the transom. AT idle it did not leak only under pressure, it would shoot out against the bulkhead and run down and turn on the pump. Good luck
 
While running check your exhaust. Mine had a pin hole in the stbd exhaust way back by the transom. AT idle it did not leak only under pressure, it would shoot out against the bulkhead and run down and turn on the pump. Good luck
I had this occur as well early in the first season on my boat. It prompted me to change all 4 exhaust tubes as well as shutters , also changed all cooling system hoses including the ones that feed the water heater. . A failed exhaust tube can sink s boat. My pinholes tube was easy to tear completely apart along the seam when I replaced them . These hoses and tubes are critical and replacing all was best 500 dollars worth of parts I ever spent
 
I have 500 Sundancer. I have mystery bilge water, too. Just traced & located a trickle of water when diesel is running. Traced to aft of starboard waste tank & battery ledge compartment, next to engine and leaking from sm weep hole. What's inside? rubber hose or fiberglass tube? Before I open top of ledge, anyone have any idea where to locate leak?
 
Put a GoPro camera in the bilge while you're underway.
 
Since we boat in saltwater if it's not apparent where it's coming from, I taste it to check for fresh vs. salt... I saw you are in the Great Lakes so that's not going to work for you, but maybe some the other guy's with mystery water might try it.
 
Since we boat in saltwater if it's not apparent where it's coming from, I taste it to check for fresh vs. salt... I saw you are in the Great Lakes so that's not going to work for you, but maybe some the other guy's with mystery water might try it.

I take it you've never had a holding tank or head plumbing issue...
 
I was doing some reading on leaks since I also have a slow leak, and there's alot discussion on the steering pin seal leaking. If you can lift up on outdrive and it has slop then the pin is wore out and needs replacing. Checked mine today and the starboard is nice and tight but the port has alot of slop so looks another big project.
 

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