When do you replace your manifolds?

Sea Ray 300

Senior Sea Ray Enthusiast
Oct 12, 2006
612
Scituate, MA
Boat Info
2005 300 Sundancer
Engines
Twin 5.0 liter with Bravo III drives.
Hi folks.

It's been a while, but I thought I'd check in.

My 2005 closed system cooling 300 Sundancer has been in the salt water for 8 seasons now, from 2006 to 2013. I've still only got about 100 hours on her, as she's more a cabin than a cruiser, and we use our small boat allot more.

Water temp up here averages upper 50s to lower 70s, and our season is 5 months long.

Years ago, when I had raw water cooled boats, I'd do the manifolds and risers after 7 seasons, but with fresh water cooled, I was wondering what the consensus is.

And I'm not sure exactly how much is actually fresh water cooled. Just the block? Or the block and the manifolds?

What about the riser?

My mechanic, when I asked him a few years ago, told me that on the newer boats, 10 years is common.

But a friend just lost an engine when his manifold failed (raw water cooled), so it got me to second guessing.


I'm told that manifolds are allot more $$$ now than they were years ago, so I don't want to do it until I should, but I don't want to chance anything eather.


What do you think?

Thanks in advance.
 
It sounds like it is time to B.O.A.T. You are at the point where you will need to replace or at least take one off and inspect.
 
Steve, I think it may be time, I have a dock neighbor with a 2004 360, buzzards bay boat, saltwater kept doing an engine overhaul because of a manifold failure. Original manifolds. I looked at the manifolds and it was past time. Not looking forward to it but I am planning on replacing mine next spring on an 06. Better safe than sorry..
Jason
 
If it were me, I would replace them. I plan on replacing mine in the next month. Mine were replaced in 2009. I just purchased the boat this year, and I would like to know exactly were I am in relation to the manifolds. Yes, I wish they were cheaper, but manifolds are a heck of a lot cheaper than a new engine.
 
If you have a half fresh water system that anti freeze is only in the block then you are due for both manifolds and risers. If full fresh water cooled and only the manifolds also have anti freeze in them then you are due for risers only. these opinions are based just on the age of the motors not usage. If your mechanic can't tell which system you have then you need another mechanic. :smt101
 
A visual inspection of your heat exchanger will reveal whether you have a full or half FWC system. On a full system, a hose delivers raw water to the heat exchanger and then hoses at each end of the heat exchanger take the raw water straight to the exhaust elbows. All other hoses will contain coolant. Locate one of the coolant hoses from the heat exchanger and hold it with one hand while holding the hose connected to the lower side of the manifold with the other hand and squeeze one of the hoses - you should feel the pressure if they are on the same system. You could also disconnect the water hose at the base of the manifold, you will be able to tell if it is coolant (FWC) or raw water. Similarly, if you have a riser before the exhaust elbow it is likely to be plumbed the same as the manifold. This can also be checked with the squeeze test.

I have a Seacore 350 Mag and both the manifolds and risers are FWC and dry joint type. The raw water is pumped out through the exhaust elbows. I am about to replace my elbows and gaskets as a preventative measure and inspect the manifolds and risers at that time, however, with the full FWC set up, manifolds and risers should not need replacing, just the elbows.

Also, to avoid confusion, it should be clarified that a riser is a separate part between the top of the manifold and the exhaust elbow, raising the height of the elbow to prevent sea water entering the elbow via the exhaust. You often hear people speaking about replacing manifolds and risers. If so, they would be replacing manifolds, risers AND elbows.
 
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I replaced my manifolds and elbows (closed cooling system) on my Amberjack last winter. They were in bad shape. The boat was a Florida boat from 2006 to 2010. I got my replacements from Michigan Motorz. It was about $2k in parts to do both engines with all mercruiser parts
 
I have a raw water system in our 280, 5.0 MPIs so this may not be a like for like and it's an 03. We did everything last winter. What we noticed was a water stain running down below the gasket where the riser met the mainfold. I thought it was more of just water overspray from when I was cleaning out the bilge and got things wet. Further investigation that was easier to see when the engines where out was paint 'blistering' or missing in small areas on the elbows (not so much the mainfolds) as a result of the passages becoming blocked and then heating up. I too am a dry-joint set up. Mind you I did not have any issue with indicated temperatures when running. My engines were out at the time for the swivel pins to be replaced so it was a good time to inspect. Thankfully I did. Once the elbows were off it was evident that they were done because of the blistering as well as blocked water passages and excessive flaking of the iron inside the passages. Expensive winter from a work standpoint but as was mentioned above, it's cheaper than an engine.
 
I am in the process of purchasing a 2006 340 Sundancer with twin Merc 8.1L (FWC block system). The boat has been in salt water on the west coast its whole life and has around 100hrs on the engines. The engine survey was performed and there were no major issues (other than alignment which is being taken care of). Compression test was good.

I asked my mechanic (who I trust) about replacing the manifolds and elbows. He thought that it wasn't time yet and there were a few more seasons on them. He said the sign they needed to be replaced would be evicence of water/rust at the dryjoint between the manifold and elbow. There is currently none and the engines look to be in excellent condition. No corrosion at all.

Is examination of the dryjoint area a reliable "source" to look at when deciding on replacement?

I am not sure how lucky I feel, but would like to avoid an unnecessary fix. At the same time, I'd rather not replace an engine. :)

Thanks for the input.
 
I am in the process of purchasing a 2006 340 Sundancer with twin Merc 8.1L (FWC block system). The boat has been in salt water on the west coast its whole life and has around 100hrs on the engines. The engine survey was performed and there were no major issues (other than alignment which is being taken care of). Compression test was good.

I asked my mechanic (who I trust) about replacing the manifolds and elbows. He thought that it wasn't time yet and there were a few more seasons on them. He said the sign they needed to be replaced would be evicence of water/rust at the dryjoint between the manifold and elbow. There is currently none and the engines look to be in excellent condition. No corrosion at all.

Is examination of the dryjoint area a reliable "source" to look at when deciding on replacement?

I am not sure how lucky I feel, but would like to avoid an unnecessary fix. At the same time, I'd rather not replace an engine. :)

Thanks for the input.

You seem to have done you due diligence by asking people that know more than I do but I'm surprised by your mechanics response. After seven years in salt water I think that I would want them pulled and inspected. My boat is a 1995 and previous owners had to replace the engine twice for water intrusion - in 2001 and 2007. A different engine, no FWC and more hours than your example but I'm not sure that I would take on the risk. The surveyor apparently didn't mention them either so I may be way off.
 
I can tell you from my direct but small sample experience.
My current boat,purchased last spring, had spent its entire life in high salt from eastern long island to Boston harbor.
The motors surveyed great at 300 hrs and still had original aluminum manifolds. After running the boat from Boston to New Jersey, I changed the manifolds to Mercury cast iron.
The aluminum manifolds had some paint bubbles on the outside and close examination showed that they were getting thin under the paint. The Mercury shop I purchased my new manifolds from had a boat with 8'1s on site where the manifolds had failed and leaked to the outside. The motors had not been damaged. The shop said they were designed to fail that way if all goes right.

I had changed the manifolds on my previous boat (350 mag closed cooled) at 8 years and they looked really good. I boat in brakash water.
I expect my new manifolds to go 10 years under these conditions.
 
I wonder if storing a sea core or fwc boat on a lift & flushing the rwc parts after use makes any difference in the lifespan of the rwc parts?
 
I wonder if storing a sea core or fwc boat on a lift & flushing the rwc parts after use makes any difference in the lifespan of the rwc parts?

It can't hurt!
 

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