1989 Formula 26PC Twin Mercruiser 4.3LX, Alpha I, Gen 1 - Water Leak at/in Transom Assy

[PosessionSound26PC]

Situation: Old boat that now has a leak at the transom assy/exhaust.

I replaced the starboard impeller pump a while ago after some engine overheating issues (see last post: https://forums.iboats.com/threads/1989-mercruiser-4-3-lx-alpha-1-gen-1-overheating.767141/). On the previous cruise (a few weeks ago), I noticed that the boat was slowly taking on water in the bilge - I could see it rising visibly over about 5+ minutes as the boat gently rocked in the water at the dock (the water sloshed an inch or two higher along the curve of the boat as I waited). Took the boat out and have since noted the following:

1. Ran an engine cooling test on muffs - didn't notice any water leaking into bilge as the engine warmed up and temp leveled off at 150F. I DID notice some fumes/smoke in the engine compartment after the engine warmed up but assumed this was just some anti-corrosion spray I had put on part of the front of the block where I had removed some rust recently...

2. Put boat back in water, plug in place with Teflon tape to boot. While still on the trailer and with water reaching just under the swim platform (roughly where it rises to when boat is fully in the water and level), I saw a fairly sizable stream of water on the inside of the transom, roughly at engine mid-line, slowly filling up the bilge. I would say it was about as fast as a drinking fountain stream, maybe a bit faster. I should have done a more thorough inspection but a quick peek over the back of the engine didn't indicate any water - the water inlet hose from the impeller pump seemed dry and I didn't see anything else from above. Pulled boat out and the bilge pump worked for a while to get it all out.

3. I previously had a seized gimbal bearing about 3 years ago and thought maybe I had a failed U-bellows or it came unclamped/etc. Pulled the drive and saw and felt NO water at all in the U-joint cavity, also no rust or indication of failure. Also can't imagine that big of a stream of water getting through the tight fit of the drive shaft... Water passage O-ring was in place, gasket between outdrive and gimbal assy was in place.

4. The shifter bellows and its clamp and crimp APPEAR fine but haven't taken them off... didn't see any tears and the rubber I can see appears supple and un-cracked.

5. The exhaust bellows obviously had some water in it...

6. Back in 2020, I removed the exhaust risers, one exhaust manifold and the large rubber and aluminum exhaust tubes just aft of the risers. At that time I replaced the risers and the flapper valves. I checked all of those exhaust connections - everything is tight.

7. I used a mirror and light and looked at the Y-pipe that takes exhaust down and through the transom - didn't notice anything OBVIOUS in the areas I could see above or below but visibility is limited.

8. Looked at the transom assy outside the boat: the caulk around the perimeter appears as good as on Port, no obvious holes/gaps (one small one that doesn't look like it could allow that much water and I assume there' more caulk in-between the two parts...). No obvious cracks, etc. The area where the trim wires go through the transom APPEARS ok, nothing obviously wrong, though visibility is bad having not removed the gimbal assy.

What could be leaking so bad?
Is the Y-pipe known to crack and leak at the base?
Would this also explain the possible exhaust smoke I saw during the last cooling test?
Is there a way to pressure test the exhaust?
Is the Y-pipe one piece or two? (Haven't looked at the manual yet)
Can it be R&R without removing the motor?
Any other thoughts?

Thanks.

 

[PosessionSound26PC]

I should add another question: With the outdrive off, can I use a hose to squirt water up the exhaust and see if any ends up in the bilge? I assume there's not much concern with getting water all the way back up to the cylinders... This would be an alternative to running some sort of exhaust pressure test.

 

[nola mike]

The wye pipes can get pieces of the flapper lodged in them that wear a hole in it over time. Otherwise rotten transom if it isn't a boot. Easy enough to pull back your shifter boot.
Transom or wye pipe, you're looking at pulling the engine either way. You can check to see if the transom shield bolts are tight, they can also corrode

 

[Lou C]

The caulk around the transom assemblies is a sign that there has been a problem for a while, with a transom & transom assembly in good shape you should never need caulk on the outside of the transom mount. This is one of the chronic headaches of I/Os they can leak from several areas in the transom mount (steering arm, d/s bellows, shift cable bellows, y pipe & y pipe seal) and a rotten wood core in the transom itself. No easy way to fix this unless it’s either the d/s bellows or shift cable bellows. Anything else the engine has to come out…

 

[Roadking57]

I had the same type of problem with my 1988 Regal. V6 4.3L . I bought it used and the P.O. said it may have a bad transom. I replaced the bellows because he said he had never done it. Turns out it was the lower two bolts that are aluminum anode designed to corrode before anything else. If you can get to the nuts on the inside of your transom plate you can check to see if they are tight. If they seem more loose than they should be then you can bet the transom has rotted because at the factory they are tight.
Unfortunately mine were finger loose and my transom was rotted on the bottom.

 

[PosessionSound26PC]

The wye pipes can get pieces of the flapper lodged in them that wear a hole in it over time. Otherwise rotten transom if it isn't a boot. Easy enough to pull back your shifter boot.
Transom or wye pipe, you're looking at pulling the engine either way. You can check to see if the transom shield bolts are tight, they can also corrode

Will pull back shifter boot. I changed the flappers a couple years ago and the old ones were intact. Given the amount of water I'm seeing, it's likely coming in at the exhaust.

 

[PosessionSound26PC]

I had the same type of problem with my 1988 Regal. V6 4.3L . I bought it used and the P.O. said it may have a bad transom. I replaced the bellows because he said he had never done it. Turns out it was the lower two bolts that are aluminum anode designed to corrode before anything else. If you can get to the nuts on the inside of your transom plate you can check to see if they are tight. If they seem more loose than they should be then you can bet the transom has rotted because at the factory they are tight.
Unfortunately mine were finger loose and my transom was rotted on the bottom.

Not much room under motors but was able to shine phone light upward and use mirror to see at least one corroded bolt at bottom of transom - it had that greenish/whitish corrosion on it. Will check for looseness if able...

There's gotta be a good size hole somewhere though given how much water I'm seeing and the only places left are shifter boot, steering arm and exhaust, the latter being more likely. I didn't see any water at the steering arm when I looked... Will have to keep poking around there. Thanks for the input guys!

 

[nola mike]

Not much room under motors but was able to shine phone light upward and use mirror to see at least one corroded bolt at bottom of transom - it had that greenish/whitish corrosion on it. Will check for looseness if able...

There's gotta be a good size hole somewhere though given how much water I'm seeing and the only places left are shifter boot, steering arm and exhaust, the latter being more likely. I didn't see any water at the steering arm when I looked... Will have to keep poking around there. Thanks for the input guys!

It can come right through that bolt hole. Wiggle it from the outside. Tough/impossible to get to from the inside.

 

[PosessionSound26PC]

It can come right through that bolt hole. Wiggle it from the outside. Tough/impossible to get to from the inside.

Ah, yes, good point. Didn't think about it because on the outside those bolts have some sort of plastic cap and appear completely sealed. But maybe they're just faking it and are in fact loose. Will report back!

 

[nola mike]

Ah, yes, good point. Didn't think about it because on the outside those bolts have some sort of plastic cap and appear completely sealed. But maybe they're just faking it and are in fact loose. Will report back!

They have the anode on it. You can grab it with vice grips. If it's that corroded, the bolt will snap before the anode unscrews. The only thing keeping water out of there is a small gasket

 

[PosessionSound26PC]

They have the anode on it. You can grab it with vice grips. If it's that corroded, the bolt will snap before the anode unscrews. The only thing keeping water out of there is a small gasket

Looks like the two bolts either side of the hydraulic block are NOT anodes on my boat, they are actually plastic waterproof seals over the bolt heads. Instead, I have the integral Mercathode style that has an electrode assy mounted to the outside (underneath) of the hydraulic block. There is an O-ring or rubber grommet that seals off the hydraulic line cavity in the transom assy from water intrusion. Will have to check that out.

 

[PosessionSound26PC]

Also ran across this interesting video of the same general problem - how to find a water leak in/through the transom area: fill the boat with water and see where it comes out:

I don't fancy getting my new starters wet though, even though they are supposed to be marine grade (sealed?). Maybe on the boat ramp to keep the water away a bit more...

 

[nola mike]

Also ran across this interesting video of the same general problem - how to find a water leak in/through the transom area: fill the boat with water and see where it comes out:

I don't fancy getting my new starters wet though, even though they are supposed to be marine grade (sealed?). Maybe on the boat ramp to keep the water away a bit more...

Do a search on here as to why many think this is a bad idea...

 

[JASinIL2006]

Terrible idea to fill your boat with water. Not only will water get in all sorts of places where it should not be, but the water in your boat will not represent the same pressure against whatever it is that’s leaking when the boat is floating. Bad, worthless advice.

 

[PosessionSound26PC]

Terrible idea to fill your boat with water. Not only will water get in all sorts of places where it should not be, but the water in your boat will not represent the same pressure against whatever it is that’s leaking when the boat is floating. Bad, worthless advice.

Fair enough, will avoid.

 

[PosessionSound26PC]

Update: Poked around trying to find the leak - the key was the amount of water flowing into the boat: similar to a drinking fountain, maybe more, and it got through quick, not like it was seeping through rotted wood. It would have to be a decent sized hole for that to happen. After removing the outdrive, I used a drain inspection camera to look up the exhaust and as far as it would fit into each drain hole on either side of the transom assy. Nothing unusual but couldn't push it in very far. Used the camera inside the bilge to look at the Y-pipe but also didn't notice anything obvious, although the lighting and resolution were not great so easy to miss something...

I then used a 5 gal container of water on the swim deck connected to a hose shoved into the exhaust, a rag around it to block water leaking back out and also plugged the two drain holes on the transom assy. Opened the valve on the container and sure enough, quickly got a nice stream of water coming out of the bilge drain hole. Went into the bilge w/ the camera and got video of water streaming out of what appears to be a small hole (3/16" dia?) on the bottom surface of the Y-pipe directly above one of the two transom bolts that come in from the outside (the tail of the bolt and the nut are visible below the leak/hole, page 6C-5 of the Mercruiser GM V6 1983-1993 manual I got form this site). I have attached the video to this post.

Not sure how a hole formed there, probably corrosion? I am getting a quote for replacing the Y-pipe although I thought about doing it myself after seeing someone rig up a couple of wooden beams above the engine compartment and using a chain hoist to lift the motor and then slowly tap the beams forward to move the motor out of the way. I have enough room forward to do this but I have two motors whereas he had one so not sure if I can get in behind it to do the work. Removing the engine hatch/lid may be possible w/ 2 people... Would probably replace the engine mounts at the same time.

A MUCH cheaper and faster alternative, IF I can manage to get myself under the motor far enough, is to feel around for the hole, clean the area w/ acetone and sand paper, clean the edges of the hole w/ a small file, and use ExtremeHeat compound from JB Weld to plug it. I will probably try this regardless since I can do it relatively soon and it will be easy to tell if it worked or not.

 

[Lou C]

I would not try to lift the engines myself, there's a lot that can go wrong with doing that, and the "wrong" can be really bad with 600 lbs starting to move when you don't want it to.
Might look at it this way, how long will you keep this boat? If just a few years, try the repair you described above, that might work because the Y pipe while full of water isn't under a lot of pressure.
If keeping for a long time I'd do it the right way, which is a major job, pulling engines, checking transom, replacing anything in the transom assemblies that is questionable. Depending on what you find, could be a very big job, but once done, you're good for a very long time.
It is things like this that would stop me from buying another I/O boat. They just have too many places that can leak water.

 

[PosessionSound26PC]

Agreed @Lou C - I have pictured that motor in my head, hovering in the air next to me while I'm in that confined space... gives me the willies! I don't plan on keeping the boat a long time - it is old and I bough it as a cheap way to get on the water and experience boating / get my feet wet. I am doing that in spades but mostly on land it seems!

Will definitely proceed w/ the JB Weld and report back.