Leak through transom

[ryno1234]

1998 MerCruiser 5.0 with Alpha 1 Gen II

I have a slow-ish leak through the transom. About every 5 seconds I'll get a quick, thin stream of water. I can take the boat out for 3 - 4 hours and I'll have about 3/4 inch of water in the V of my bilge.

Ideas on what this might be? I checked the bellows but they appeared fine. I'll re-check them more thoroughly as soon as I can (boat is at storage at the moment).

Any ideas of where to check first?

I'm also now concerned about transom rot. I've taken it out twice while it has been doing this. How real is that concern? This is a fiberglass hull cabin cruiser.

Thanks in advance.

 

[airshot]

When a transom starts to go soft the wood inside begins to collapse and allows water to come in a round the seal. Tightening the bolts only compressed the wood mire and can create an even bigger leak. Hopefully you will find something simple Like a leaking hose clamp somewhere.

 

[nola mike]

IMO that's transom rot until proven otherwise. I'd drill some test holes around the area and see what you come up with. Does the leak happen when sitting or only with the engine running?

 

[ryno1234]

IMO that's transom rot until proven otherwise. I'd drill some test holes around the area and see what you come up with. Does the leak happen when sitting or only with the engine running?

The leak happens while sitting. These screenshots were while in the water, but engine off

 

[ryno1234]

When a transom starts to go soft the wood inside begins to collapse and allows water to come in a round the seal. Tightening the bolts only compressed the wood mire and can create an even bigger leak. Hopefully you will find something simple Like a leaking hose clamp somewhere.

Is there always wood in the transom? From what I understood, we're straight fiberglass, but I suppose I could be wrong about that.

UPDATE: Never mind - looks to be wood transom https://www.maxumownersclub.com/forums/f18/transom-question-4975.html

 

[ShoalSurvivor]

I just went through this myself. Full thread:
https://forums.iboats.com/threads/alpha-1-gen-2-leak-transom-service-questions.780501/

the overall consensus was that it was rot. in my case it was not.

i eventually found the source to be in the well at the very bottom of the transom bracket where the trim hydraulic lines penetrate. The drips in your photos are coming from the same place mine were. It's either a leak in the hydraulic line manifold (worn gasket), Y-Pipe corrosion, y-pipe o-ring, or the transom seal.

in my case, I struck the drive backing out of my driveway and knocked the transom seal loose. The seal was 25 years compressed and flattened… only working because it was undisturbed.

I didn’t want to drill holes in my transom, but doing so did inform my investigation And holes were easily resealed.
you can also do a hammer test on the exterior of the transom to listen changes In density.
when I removed the transom bracket, I was able to fully evaluate the transom material.

i dried and glassed over the cutout and tested the compression of the transom (around the bracket), then popped in a new o-ring and reinstalled. I added sealant to the outside perimeter just for good measure.

the 8 bracket bolts are only torqued to 22ft Lbs.. which is nothing.

the other area to check is the y-pipe. You can feel and tap all around it (especially underneath) to see if it’s compromised.
if you’re leaking when running on on muffs, it’s likely not an exterior penetration.

A boroscope is cheap and helpful. Also, look carefully at interior side all the penetrations : oil monitor, water tube, trim wires, speed hose

if you think it’s the seal but not rot, you can apply some marine sealant around the exterior bracket to rule out the source, (it will stop leaking), but if that’s the case, it means you need to reseal it properly.

one last spot to check is the trim hydrailic manifold. Beware though, if you crack that seal, and the connections are rusty, it can be a ***** to replace the gasket. If that IS the problem, you’ll also find water inside in the very bottom of the bracket where the lines penetrate.

don’t panic. investigate first. But deal with at ASAP. if left unchecked, water would have rotted my transom.

 

[ryno1234]

Thank you so much for this information! @ShoalSurvivor! This is incredibly helpful

 

[ShoalSurvivor]

Sure thing. I just updated my post and would really just focus on "It's either a leak in the hydraulic line manifold (worn gasket), Y-Pipe corrosion, y-pipe o-ring, or the transom seal." first.

depending on how long it's been leaking, and what you find, you can deal with the rot investigation once you know the real source.

you can test it out of the water by filling water into the Ypipe. If it leaks, it could be corrosion or the o-ring. if you fill that "well" with water from the inside (and add some food coloring) and it leaks out of the hydraulic manifold or around it, you'll know its the manifold. If it leaks out of the transom edges, you'll know it's the seal. If none of the above, add sealant around the bracket and take it back to the water. If it doesn't leak, it's your bracket seal.

 

[bruceb58]

I just fixed a friends boat that this was happening to. In his case it was his u-joint bellows leaking. When was the last time you changed yours? You store the boat with the drive up or down?

 

[ryno1234]

I just fixed a friends boat that this was happening to. In his case it was his u-joint bellows leaking. When was the last time you changed yours? You store the boat with the drive up or down?

Bellows were changed probably 3 years ago. I store with the drive up.

 

[airshot]

Bellows were changed probably 3 years ago. I store with the drive up.

Better for the bellows if stored down, far less stress on them