Manifolds and risers....

J

joenofish

New Member
Dec 14, 2010
55
St. Petersburg, FL
Boat Info
300 Weekender
Engines
Twin 260 Mercruisers
I bet if I spent enough time I'd find the answer to this question soemwhere in here..It seems like a lot of saltwater boats I see for sale state that they have just replaced the manifolds and risers...Why? Is this something I need to think about on my old '86 300 with twin freshwater cooled mercs?
I have 800 hours on the engines. How would I know if I need to do something?

Thanks,

Joe
 
Hopefully someone else will chime in with more info but I have been wondering this myself.

I understand that the exhaust elbows can corrode internally. And, if it gets bad enough they can develop holes in the walls that will allow water to enter the engine.

In salt water this corrosion can happen fairly quickly and these parts most be checked often. (new parts once every 3 years and if they are OK, then inspect them every year until you replace them then go back to the same 3 years, every year routine)

However, I have not found any schedule inspection timeline for freshwater engines. Nor, have I been able to determine if it is just the elbows you mostly need to be concerned with or the manifolds and risers too. My boat does not have risers, and from what I have researched the manifolds are not as likely to leak as the elbows???

I was considering removing my elbows and inspecting them here very shortly. I sure would like to learn more about this before I start tearing into anything. Most of the info I have found has come from this forum, and it sounds like it would be a good idea to take a look at my exhaust elbows. But other local fellow boaters that I have talked to don't think I need to take mine off yet since it is all freshwater use (my engine has 400 hours).

If you do take them off, you must be careful to use the correct gaskets (they have changed slightly over time). And I have read that you should be sure that they are genuine Mercruiser gaskets.

I don't want to create a problem if I don't have one. But, I don't mind the work as long as the time is well spent.

As I said, hopefully someone will give us a "Manifold, Risers, Elbows and Gaskets for Freshwater Engines 101" class!!
 
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Hi Guys,

I was also a little in the dark on this topic. I got a pretty good explanation by Frank Webster on this topic. I'm not sure how it relates to fresh water boating but it may give you a baseline. Here it is, I hope it helps:

11-20-2010, 09:29 AM
fwebster
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Whats This?
Join Date: Oct 2006
Location: Middle Tennessee/NW Florida
Boat: Sea Ray
Details: 1996 450DA
Engine(s): 3116 Caterpillars
Posts: 5,065


Re: 97 330DA Possible Purchase - Very Confused - Need Some Help -
Todd,

There seems to be a "standard" 5 year plan regularly mentioned, but I don't think there is a hard and fast rule on timing for manifolds and risers since a lot of the variables depend upon location, salinity, temperatures, type of cooling, etc. In Florida, we are in a horrible spot for risers/manifolds......i.e. hot weather, 12 months a year boating, and high salinity. Here is what works best for us: On original manifolds and risers, after the 3rd season, remove the risers and check the castings for corrosion. If they look good, put on new gaskets and button them up and go boating. After that initial check, begin checking the risers every year. When you need to replace them, do them all and do it with Merc OEM parts. Once you are on new castings, go 3 years and begin the annual checks all over again. Using this plan, it is unusual to ever need to replace manifolds because you will be preventing moisture from ever getting to them and you will be keeping the riser to manifold gasket surface dry.

If a manifold is going to fail, it will be at the riser to manifold mating point or in the bottom of or upper end of the runners and it is easy to see those points without removing the manifolds from the engine.

Checking the risers and manifolds is easy and only costs a gasket per side and you can check all 4 in 1-2 hours, so even if you hire a mechanic to do it, it is cheap insurance from a forced repower.

I don't think FWC helps with corrosion in the exhaust system. I certainly does eliminate corrosion and sediment in the engine block cooling passages thus adding tons of engine life. It may also help you to realize that the corrosion that ruins the riser (and eventually the manifold and engine) usually begins in the exhaust passage, not in the cooling or water side of the riser. The exhaust passage is open and exposed to whatever ambient air your boat sits in. For you, with your boat in the water, the air working its way back up in the exhaust system is coming from about 3" above whatever water you are sitting in. That might make it a pretty salty environment up in the exhaust system.

FInally, most riser leaks do not come from the riser casting, but from the riser to manifold gasket. It is narrow and thin and will burn to the point of becoming brittle. By checking your risers annually, you are replacing this gasket every year.

Hope that answers your questions.............
__________________
Frank
 
I've got a question ? on my 390 I have a pair of big blocks,and plenty of room to check the inboard side of both eng. by checking one bank on each eng.:huh: give me a good reading of what is going on inside also same with spark plugs..Thanks .....Rip
 
I was starting to think my question was so dumb no one would reply! Because my boat is new to me, and I have the ability to pull the manifolds, I think now would be a fine time to do this. I'll pick up new gaskets, pull the covers and dig in. I also need to scrub the engines, can get it all at once. I wish I would have done this a month ago when I changed the oil and fuel filters and did the genny service.
I cartainly don't want to scrap an engine over a lack of maintenece issue. I do my best to take good care of them.

Thanks for the help, I'll reply to this post with the pics of the work as soon as I do it. (also how long it took me)...

Joe
 
tdschafer said:
Re: 97 330DA Possible Purchase - Very Confused - Need Some Help -


I don't think FWC helps with corrosion in the exhaust system. I certainly does eliminate corrosion and sediment in the engine block cooling passages thus adding tons of engine life.

------------------------------------------

I believe the major problem with salt water use is caused from the salt precipitating out of the water when it sees the heat of the manifolds and risers. The heat also breaks down the salt and forms chlorides. Chlorides are nasty on metal, causing very acceleratied corrosion as the concentrations build up. Not only does the metal corrode overall, but you also get locaized "pitting" in the metal that traps some of the chlorides in the hole. When more salt water sees this heat, it gives up more chlorides and the local concentration of chlorides at this spot increases exponentially and just compounds the problem. This is the major reason you need to flush your engine after use in salt water, not just for the sediment or dirt.

With engines operated in fresh water, you don't have this chloride problem, which is the reason the manifolds and risers last longer.
Click to expand...
 
Joenofish,

Are you in Patrician Point by chance?
 
Bucit said:
Joenofish,

Are you in Patrician Point by chance?
Click to expand...

Bucit,

No, not sure where Patrician Point is. We are about 1 mile from John's Pass not far from Madeira Beach. Our boat (new to us) has been around St. Pete for years, it spent the last ten years in the Venetian Isles area (just south of the Gandy Bridge on west side of Tampa Bay).

Best Regards,

Joe
 
joenofish said:
Bucit,

No, not sure where Patrician Point is. We are about 1 mile from John's Pass not far from Madeira Beach. Our boat (new to us) has been around St. Pete for years, it spent the last ten years in the Venetian Isles area (just south of the Gandy Bridge on west side of Tampa Bay).

Best Regards,

Joe
Click to expand...

Patrician Point is in between Ventian Isle and Snell Isle. Boating through our canals I saw a home that was foreclosed on and the boat sat there for a while and then it moved to a different house. It was a 300 Weekender and thought maybe that was you. Maybe we'll see you out on the water this summer.
 
Great info, and thanks for the repost of Frank's message.

I had the mating surface between riser and manifold begin to fail on my 175, 3.0l engine last year. When I changed the spark plugs at the beginning of the season, I noticed the #4 cylinder spark plug looked very different than the rest. But hard to indicate what was wrong...it wasn't fouled and it wasn't completely dry either. So I kept them on the workbench.

Two weeks later, I take a look and that spark plug is now clearly rusted. So what had been happening was that water was beginning to get through the exhaust valve of this cylinder (nearest the elbow) and into the chamber. Thankfully I caught it and figured it out before it was too late. There have been some threads on here that shows what happens when you don't catch it.

When I removed the elbow, that mating surface was corroded bad!

Tom
 
Still wondering how often freshwater boat engines (not just fresh water cooling) need to be inspected??

My boat is never left in the water overnight (I thought I read somewhere that that can also accelerate the corrosion).

I guess I should pull mine off and look at them...Doesn't look like a hard job at all just don't want to create an issue if I don't already have one.
 
Searay,

I don't think that pulling the risers and inspecting them will create any issues that aren't already there. I suppose when you re-assemble you could have a leak, but I wouldn't consider that a real issue, just have to tighten them up or at worst do it over. If you are concerned, then I think the possible leak is worth the peace of mind you will have by doing the inspection and knowing what you have.
 
I think I will go ahead and just get this done...

Can anyone tell me the latest Mercruiser part number for the manifold / elbow gasket for a 1999 5.0L EFI?

Engine Serial Number is OL380364.

Just want to be sure I get the correct gasket.

Thanks!
 
On saltwater engines, the salt corrodes the cooling passages, and ultimately the mating surfaces quicker than in fresh water. This causes the cooling water to leak into the exhaust side of the manifold, and be ingested into the engine (reversion). Go to www.yachtsurvey.com and read what Pascoe has to say about it. It might clear it up for you further. He's very anti-Sea Ray, and hasn't learned that every boat isn't a Buddy Davis, or a Viking, but he's still knowledgable. Manifolds and risers last much longer in freshwater. I know people that have all the original stuff, in freshwater from '87 with no problems yet.
 
You could do what I did by going stainless steel .Exspensive but long lasting added hp
 
Just an update......

I pulled both elbows off my engine and inspected them. They looked like new.

1999 5.0L, only freshwater use...
 
surfinjoe said:
Silly question, but why don't they paint the INSIDE as well?
Click to expand...

Better yet, why don't they ceramic coat them inside and out...kind of like exhaust headers on performance cars and boats? I would think they'd last longer and be more protected from the elements on both sides...
 
Gunn said:
Better yet, why don't they ceramic coat them inside and out...kind of like exhaust headers on performance cars and boats? I would think they'd last longer and be more protected from the elements on both sides...
Click to expand...

If they built them to last they would lose money in parts replaement and repair labor.
 
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