Cobra water leak - how to diagnose?

I've had the boat in my signature for two seasons. I replaced the bellows in 2010. It used to run bone dry; not a drop of water in the bilge after a day out. This season I noticed a pint or two of water collecting in the bilge and wondered how it got in. Yesterday it got much worse; the bilge started filling enough to trigger the bilge pump about every 5 minutes.

I looked (as best I could) at the transom assembly from inside the boat and could see water running in. I couldn't tell where it was coming from exactly. The water was coming in while the engine was off. The two likely candidates are a faulty bellows or a failed transom housing seal.

Can anyone suggest any other source, and a way to determine where the problem lies? I can try filling up the bilge while the boat is on the trailer and see where it comes out, but then I can only fill it as high as the bottom of the starter.

FYI, the lower unit was rebuilt in fall 2010. Everything except the drive internals and the bellows are original to the boat.

Re: Cobra water leak - how to diagnose?

The ONLY way you are going to find a leak of any kind, is to get in there and look (and listen). Use a digital camera, or mirrors and flashlight.
It may not even be the drive or transom shield leaking.

You could have water leaking in the seam between the hull and the deck, or maybe a screw on the transom, or .................

Re: Cobra water leak - how to diagnose?

Don S said:

It may not even be the drive or transom shield leaking.

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During my initial examination I was able to see water coming in from the bottom of the transom assembly. The only penetrations I'm aware of are the driveshaft hole, the exhaust hole, the cooling water hole, the shift cable hole and the trim sensor wire hole. If it's not one of those I assume it's the seal between the transom assembly and the hull. Did I miss anything?

I already pulled the drive to examine the bellows. I was hoping to diagnose the problem without having to reinstall the drive and put the boat in the water.

Re: Cobra water leak - how to diagnose?

had an OMC V8 a little older I think, but not much that the bottom left corner of the Y pipe was corroded and water was pouring in looked like it was from the bottom of the shift cable housing..,

btw the replacement Y pipe had instructions from OMC to not install flappers and had no provision for flappers.

had another boat that when I first diagnosed the boat leaked alot from behind the engine, took the engine out, NO leak..

tightened up the transom plate bolts, leak fixed.

Re: Cobra water leak - how to diagnose?

Kainon said:

had another boat that when I first diagnosed the boat leaked alot from behind the engine, took the engine out, NO leak..

tightened up the transom plate bolts, leak fixed.

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Yeah, I was hoping to avoid having to pull the engine.

Re: Cobra water leak - how to diagnose?

I had a leak in mine, about a gallon an hour, maybe a gallon and a half. I found 2 of the six transom assembly bolts loose. One was so loose that the washer was flapping around. I tightened them up, they held torque so I assume it wasn't crushing the transom. And the leak went away. I get maybe a quart ot 2 in a full day of boating.

Re: Cobra water leak - how to diagnose?

I took my boat to the ramp today in an effort to locate the source of the leak. I couldn't see what was leaking within the boat since there's no room between the engine and the drive to see anything.
I brought the boat home and filled the bilge with water. It's leaking out of the boat between the hull and the gimbal housing.

I'm assuming this points to a rotten transom.