The Boating Forum - In-water elbow and manifold changes - sink?

Hi All,

My 26' 2002 Searay Sundancer is overheating - most likely cause is the manifolds and risers are 10 years old with 810 hrs so I'm changing them out. It's a bear to haul back to the yard so I'm thinking of doing it in the water at the dmarina.

Someone cautioned me against that manuver claiming that some boats can sink if the ports are below the water level. That sounds a bit odd as (a) anything wet seems well above the W-line and (b) if the boat depended on the functionality of it's hoses, castings and whatnots with the motor off, I would imagine more boats would be sunk at the dock.

But that's just me speculating, so I'm throwing it out there to you guys to enlighten me.

Any input would be most helpful.

Not at all, it's done all the time. I rebuilt twin engines in my fathers boat while it was in the water. Took the engines all the way down to just the block, crank and pistons.

There should be a valve to shut off intake cooling water and exhaust should not be able to back up enough to flow into the boat.

Inboard or IO? If inboard and your exhaust through the transom is partially in the water line as some are, and you let the hose that you pull from the riser lay in the bilge, you may sink your boat

Inboard or IO? If inboard and your exhaust through the transom is partially in the water line as some are, and you let the hose that you pull from the riser lay in the bilge, you may sink your boat

He has a 26' Sea Ray Sundancer. It's a single I/O. As long as he doesn't remove the Y pipe that transfers the exhaust to the drive he won't take on water. And I don't think you can remove that pipe without pulling the engine.

He has a 26' Sea Ray Sundancer. It's a single I/O. As long as he doesn't remove the Y pipe that transfers the exhaust to the drive he won't take on water. And I don't think you can remove that pipe without pulling the engine.

Correct. Would need to pull the engine to remove the y pipe, and in turn the waterline would be lower.

I have put new manifolds and risers in while in the water.

Correct! I/O 5.0L Bravo 3 set up. Still safe enough?

Thanks for your reply so far - gonna go for it unless someone say's woah!

I'm admittedly not familiar with the exhaust setup on that boat but if you confirm the exhaust hoses engine end are sufficiently far above the outside waterline, and you can secure them at that height or above while wrestling with the reluctant riser/elbows water should not enter from that source.

On my inboards , to greatly help reduce the pucker factor thought of how fast water can come in through 1 or 2 4" open exhaust hoses that could fall lower, I employ 4" OD PVC conduit rounded caps placed 3/4 in the hose and clamped so that is really safe while I work on the elbows.

As my engines are full FWC, I don't worry about replacing manifolds, but for the riser/elbows I pull the RW hose to the low-mounted oil cooler to drain RW well below the top of the ex. manifolds, pull the FW coolant hose to and from the manifold to drain engine coolant ( into containers for reuse) below the top of the manifolds , pull off the elbows 2 gaskets and block-off plates, and shop-vac out any remaining coolant visible in the exhaust manifolds' coolant passages to keep it from rocking into the exhaust hole and in through any open cylinder ex valve. .


Presuming yours are all RWC or "1/2 FWC systems" since you are replacing manifolds , I guess you'd pull the RW hose from the RW pump to 1st inlet at the engine , plug that hose or at least secure it well above the water line & preferably both, then pull the RW drain plugs on the the ex manifold and block before unbolting the heavy iron. Don't forget to replace the drain plugs.

The y pipe also has flaps in it, they close when flow is reversed.... I.e water coming in. If it was possible for your boat to sink with the risers and manifolds off, your engine would be flooded with water all the time. The y pipe, manifolds, and risers are all well above the water line. They have to be otherwise, like I said, your engine would have seawater in places it shouldn't be (combustion chamber) all the time.

As mentioned, you're good to go. The top of the Y-pipe should be above the water line so you are ok to remove manifolds and risers. When you remove hoses from the manifolds you may have to secure them up high.

won't sink, but a quick question if it is the elbows and manifolds, you can check that fairly easily. Let it idle and start to heat up, touch the elbows or manifolds and are they hot to the touch? could be other problems contributing to the overheating?
If it turns out to not be them, I have a good idea as to what it could be, the water cooling line from the lower unit comes through a steel sleave on that model. It can corrode and squeeze the supply line. Just a thought.

If the risers/manifolds are 10 years old, how old is the impeller?

HI, Im new to this forum thing and not sure if this is where this goes but my 6.2 Mercruiser is overheating only at high RPM (over 3000). I changed out the risers/elbows in 2010. tried taking out the themostat but still eventually got hot. Any ideas??