Hello, I have a mystery and was...

[Greg_B]

Hello, 

I have a mystery and was hoping someone may have had a similar experience and could offer their solution.

I have a 1989 440 CV.

Last week when filling the fresh water tanks (2x50 gal mounted midship) there was a loud tank burp from both tanks.  No water ran out the fill line to indicate the tanks were full so I left the hose on. After another period of time which should have been plenty of time to fill I discovered a large amount of water in the bilge.

I have drawings of the tanks and the fill connections, pump outlet and vents.

 All of the connections on the top of the aft tank are secure.  The fwd tank fills from the bottom corner of the aft tank.  It has one vent connection on the top opposite corner. It too is secure.  

The tank does not leak after the fill line is stopped,  so it must be running out the top of the tank, but no water is visible.

The tanks except for about 6 inches of head space are inaccessible.

Where is the dang water coming out??!!

THANKS for any help.

Greg

[wingless]

If the tanks don't leak when full, then the leak must be above the full level, such as in the supply hoses and fittings, the vent hoses and fittings or in the discharge hoses and fittings. Or, the leak has "sealed" itself.

The loud burp is the clue. It sounds like filling the tanks trapped an air bubble, that then became pressurized as the filling continued, until sufficient pressure was created from increasing the level above the air for that pressure to find a path, burping air and water.

It may be that opening is partially / fully sealed, now that the bubble is gone.

Every time I fill my water tank I stop when water spits out the vent near the fill. IMO this ensures that a dry bilge means no leak.

Why not overfill your system, up to the maximum level that it will hold, to see if water leaks?

If dry under this test, then either the prior leak is above this level, or pressure was required to force out the water / air burp.

Was the tank initially empty during the problem, perhaps trapping air down low, that then got "super" pressurized by 50 gallons of water above? When I fill my empty water tank I keep the pump powered and a tap open until normal flow is established to avoid trapping air down low.

If this low level / highly pressurized bubble was the possible problem, then could this be recreated, empty tank refilled, but this time visually observing that low plumbing while wearing eye protection? Also making a video would be handy if something happens because I frequently get bored and an event like this could be interesting.

It may be required to carefully apply a low pressure to the tank, but that is super scary because of the possible problems that would result.

[Greg_B]

Thanks very much for your thoughtful reply.
The tanks were empty when we filled them and the leak occurred. After evacuating the bilge, we pumped some water out of the tanks and allowed time to check for the leak. There wasn't one. All the vent hoses , fill line and pump outlet fittings are visible with no apparent leaks. However the tanks are not accessible at all except from the top panels. The tanks appear very solid, hard to believe it's a seam but the amount of water running out when full indicates a sizeable hole.

[gtstang462002]

I have an '87 460CV which is basically the big brother to your model. My guess is the vent on the side opposite of the fill is probably plugged and the vent hose has come loose from the top of the tank. That is where your "large" leak is coming from. If it is anything like mine, I cannot access that tank without doing some serious deconstruction to access it.

[Greg_B]

I agree on the access, it's pretty ridiculous.
I also agree the lines were apparently clogged. But i can see both vent connections and they are secure.
I'm thinking it must be a hose, but it's apparently below the top which makes it really hard to see.
Attached the sea ray drawing.
Thanks!