8.1 "dry joint" Manifolds; How do I know when to replace?

[SeadawgVB]

So I have twin 8.1 motors in my 360DA and I am approaching my second second year of ownership. I have no idea how old the manifolds are, although someone on the dock said he thought the previous owner replaced the somewhat recently. No warm fuzzy there....

How do these type of manifolds go bad?
What are the indications of needed to be changed?

A local, well respected marine mechanic told me that those stainless exhaust riser / elbows do go bad after a while and pitting inside of them will result in seawater dribbling back down into the exhaust after shutdown. I expect those are the original risers, so I'm considering swapping them out this winter. Should I just throw a set of manifolds on the motors as well???

Port side motor had been running a little warmer than starboard, but after changing the seawater pump (due to leaking seal (after swapping impeller)), temperature returned to normal and within 1 degree of starboard motor.

 

[M Prod]

I had the same concern when purchasing our 340. I just went ahead and changed them for my peace of mind. Typically how they go bad is eventually corrosion eats holes through them, and lets water into the engine. Water intrusion potential through the manifold is much less of a problem with the dry joint manifolds you likely have, but it will happen eventually. I did look inside the risers in the process, and they appeared almost new to me ...so they remain. Once I had the manifold's off, I could see the corrosion wasn't that bad and they had likely been replaced by the PO in the last few years. Regardless, now I know they're nearly a year old, and I'll replace them again at 5 years. Every 5 years in salt is a good rule of thumb. If you flush your system with fresh water after use, you could easily get more years but why risk it? A few boat bucks to replace seems like a good investment versus a potential 20 to 30 boat buck engine replacement.

 

[grettberg]

Hey Guys,

Good subject. Any timeline for doing the manifolds/risers when in brackish water? Boat is going on 15 years this upcoming season. I'm on the Gunpowder River high up on the Chesapeake River. Engine has 480 hrs on it.
Thanks

 

[M Prod]

Hey Guys,

Good subject. Any timeline for doing the manifolds/risers when in brackish water? Boat is going on 15 years this upcoming season. I'm on the Gunpowder River high up on the Chesapeake River. Engine has 480 hrs on it.
Thanks

If you haven't changed manifolds in 15 years in brackish water, it's time IMO. Manifolds (especially of the dry joint variety) can easily last longer than 5 years ..even more in brackish. But why risk it? Water intrusion is the number one cause of engine failure in boats. Others probably have differing opinions on the subject but having dealt with this first hand on my previous boat, I'm pretty paranoid about the need for keeping manifolds and risers in good condition.

 

[KevinC]

If you haven't changed manifolds in 15 years in brackish water, it's time IMO. Manifolds (especially of the dry joint variety) can easily last longer than 5 years ..even more in brackish. But why risk it? Water intrusion is the number one cause of engine failure in boats. Others probably have differing opinions on the subject but having dealt with this first hand on my previous boat, I'm pretty paranoid about the need for keeping manifolds and risers in good condition.

+1 At 15 years you may be on borrowed time in brackish. The stainless elbows may still be fine but I would at minimum pull them to inspect the manifold internals as salt water (brackish) is still flowing through.

-Kevin

 

[JVM225]

So I have twin 8.1 motors in my 360DA and I am approaching my second second year of ownership. I have no idea how old the manifolds are, although someone on the dock said he thought the previous owner replaced the somewhat recently. No warm fuzzy there....

How do these type of manifolds go bad?
What are the indications of needed to be changed?

A local, well respected marine mechanic told me that those stainless exhaust riser / elbows do go bad after a while and pitting inside of them will result in seawater dribbling back down into the exhaust after shutdown. I expect those are the original risers, so I'm considering swapping them out this winter. Should I just throw a set of manifolds on the motors as well???

Port side motor had been running a little warmer than starboard, but after changing the seawater pump (due to leaking seal (after swapping impeller)), temperature returned to normal and within 1 degree of starboard motor.

If you can’t be certain exactly when the previous owner did it then change the manifolds now and inspect the stainless elbows while everything is apart. It’s good insurance and will give you peace of mind.

 

[grettberg]

Replacing the manifolds and risers looks pretty straightforward. I'm now planning on doing this prior to splashing this coming spring. Any recommendations on where to buy the parts. I searched for posts on doing the repair and did not find much. Any suggestions or tips.
Thanks.

 

[M Prod]

Replacing the manifolds and risers looks pretty straightforward. I'm now planning on doing this prior to splashing this coming spring. Any recommendations on where to buy the parts. I searched for posts on doing the repair and did not find much. Any suggestions or tips.
Thanks.

Michigan Motorz has OEM Merc at very competitive prices. Make sure you go OEM.

There are quite a few threads on here and other forums that cover this topic. Here’s one from when I did mine that may be worth a read.

http://www.clubsearay.com/index.php...-water-pumps-and-manifolds.86662/#post-977217

 

[grettberg]

Michigan Motorz has OEM Merc at very competitive prices. Make sure you go OEM.

There are quite a few threads on here and other forums that cover this topic. Here’s one from when I did mine that may be worth a read.

http://www.clubsearay.com/index.php...-water-pumps-and-manifolds.86662/#post-977217

Thanks for the info. I'll check them out. When I tackle this, I'm planning on taking lots of photos.

 

[JVM225]

Thanks for the info. I'll check them out. When I tackle this, I'm planning on taking lots of photos.

Search around on the internet for a package that includes the gasket kit and new bolts.
As M Prof mentioned, MichiganMotorz has good prices, and another name that comes to mind is “perfprotech”. Both carry OEM Mercruiser. If you have a local marine store around give them a try too. We’ve got one near us that typically runs a special on complete kits around this time of year.
Another tip to make the job a bit easier if you’re working alone:
Cut the heads off of two of the old manifold bolts.
When installing the new gaskets and Manifolds, thread those two old bolts a couple of turns in to the two outer most threaded holes. Hang the gasket on the two bolts, slide the manifold on, then get a couple of the new bolts started.
Remove the two old bolts with the heads cut off and replace with new bolts.
This technique is better than trying to balance a heavy manifold while holding a gasket in place and trying to get a bolt started.

 

[Espos4]

Also, after you cut the heads off, cut a slot into the end of the 2 studs so you can use a screwdriver to remove them