When to replace I/O manifolds???

[shoeman]

Just got my fishing boat back after routine maintenance. Used a new shop this time and was advised by them that "I'm on borrowed time" with my manifolds on the boat's 4.3L Mercruiser. I've had the boat since late '97, have used the boat a lot, frequent use in saltwater and still using the original manifolds. Whenever the boat is in salt or brackish water I flush the engine before putting it away.

My question is, should I go ahead and replace them as a preventative or wait until I start to have a problem? Someone told me that you usually start getting an engine miss condition when they start to go. This is an expensive repair (about $1300) so I don't want to spend that money if it isn't prudent.

[74Formula233]

Do you trailer and flush religiously? If so, the manifolds will last a long time, even if raw-water cooled. However, I would personally pro-actively replace them if they are 1997. If your boat is in a saltwater slip, and it is raw-water cooled, they likely should be replaced sooner than 8 years.

What you don't want to happen is for them to start leaking water into your engine internally as they can do when they fail. I am assuming your mechanic pulled your risers to inspect for corrosion, and based his reccommendation based on that.

I would probably listen to him in your case. The 1997 manifolds "don't owe you anything" at this point

[052520]

IMO sounds like a good time to add fwc & stainless risers, only if your intentions are to keep the boat a long time. other than that ,8 years w/o replaceing in salt water , i would replace them & not be worring about a failure offshore. if it does fail, its major eng. failure alot of the times. I would at least pull the risers & check them for corrosion. but all that is just my opinion!

[auguste]

I am assuming that the water manifolds look OK to you and that they are not excessively corroded or leaking.

Use a small hammer and tap your manifolds gently . . . I believe they are cast iron . . . if the sound is dull it could be that the manifolds are seriously corroded and/or that they are filled with crap . . . if the sound is metalic and somewhat clearer, then they might be OK . . . but you have to have worked in a machine shop or as a motor mechanic to know what the different sounds are. Good manifolds do not sound like a bell when you tap them . . . but you probably already knew that

On my previous boat, I had one manifold that did not sound right when I tapped it, I took it off and found it was corroded badly and I replaced it. The other one was OK.

If you decide to have a mechanic change the manifolds, I would suggest that you look at the inside of the manifold to see how bad they are. Just so that you are comfortable.

[Garett]

Remove manifods and risers and take them into an engine rebuild shop and have them dipped cleaned, inspect and act accordingly.

[shoeman]

As further information to one of the replies, the boat is stored on a trailer at my home. As for the external condition of the manifolds, they are spotless, no rust on the exterior, but I know that's not the part I have to worry about.

Unfortunately, on this particular engine, I can't remove the risers as the manifold/riser is a one piece unit that I understand Mercury no longer makes.

[74Formula233]

Being on a trailer, and describing your setup as one piece.....

Your mechanic is probably making an educated guess about replacing them, and I don't disagree. It HAS been 8 years now, so I would at least take the entire manifolds off to inspect them. You can always reinstall them after cleaning them, with new gaskets, if they look good still

But if they look questionable at that point, then replace them. I would guess the "new" ones would end up being 2 piece units.

If you decide to replace, and can stomach/reason to spend the extra money, go with Factory manifolds. The aftermarkets last half the time at best, and you'll go thru the labor BS much sooner again.

[606zpx]

I would DEFINITELY at a minimum remove and inspect and if you dont know what you are looking for/at get someone that does. If you have a catestrophic failure it could result in your needing a new short block.

If are even mildly mechanically oriented replacement of the manifold is a pretty easy job. I am really surprised about the one piece manifold riser setup. Often times the manifolds will outlast the risers as fresh water will remain in the manifold after flushing and so keeps the air out. As a result, many folks will inspect manifolds, acid dip, paint them reinstall with new risers.

Either way I would say you MAY be boating on borrowed time but not definitely. Would defiitely inspect as this is a wear/maintenance item.

[pooldoo73]

Eight years is an awful long time on a raw water setup. Checking them would be the best thing to do and changing should not be thought of as an unneeded expense. A new engine is much more expensive. I have twin inline-6's and the expense to keep up with the manifolds/risers with saltwater use is prohibitive enough for me to convert them to closed loop cooling systems, which isn't the cheapest thing to do either, but the block and manifolds run antifreeze through them after that and the risers are the only things that need changing. If you will keep the rig for another 8 years the cooling system change may not be a bad idea.

[ken2]

You can submerge the manifolds in muratic acid for one or two days.
Check them each day, and run some water through them to see how it looks.
My father had a 1991 4.3L and his manifolds finally messed up in 2001. He submerged them in acid for a couple days, and theve been going good ever since.
I think they wanted to charge him 800 bucks for manifolds. (stock, not stainless or anything)

[KevinM]

I would just replace. You could suffer a hydrolock which will bend a rod, or if it does start leaking and it get into a cylinder it wil rust up a cylinder/s and ring/s, and it won't turn over. It's not necessarily true you will start getting a miss. Exhaust pressure could blow any seepage or leaking water out. I have seen them run fine, the boat shuts down at an anchorage, water seeps in, hydrolock, also boat runs fine, you try and use it the following week, can't becuase the cylinder and piston have rusted together. As far as fresh water cooling, it would be a waste of time, your block is already started the corrosion process.

The statement the fram guy makes pay me know or pay me later holds true. In this case the later will be a large bill!

[LouC]

I replaced the one piece ones on my OMC V-6 last spring. 16 years old and still good! I have no idea how many hours in salt this boat had, it was at least several years worth. It is not worth taking a chance even though the parts are not cheap to do this. Some warning signs are the riser section getting hotter than before, and difficulty starting. Problem is by the time you notice difficulty starting, you already have salt water in the cylinder. See if you can change to the two piece set up without having to change the Y pipe. That will make it possible for you to check the risers every so often. I like the one piece OMC design because there is no manifold to riser joint to leak. However, you can't check for wall thickness with this design. Most people say 4-5 yrs in salt is time, but some may last longer. I have heard that if you run a boat in salt more than 100 hrs you cannot change to closed cooling because the rust that flakes off in the block will clog the heat exchanger.
I fill the motor and manifolds up with no tox antifreeze with corrosion inhibitors (winter storage) in the hope of making it last longer, maybe it will!

[Sleeper]

There have been more well running marine engines ruined by a failed exhaust manifold than any other single cause, except sinking (usually caused by hurricanes).

At least pull them and clean/inspect.

[Bucktail]

You have had good luck with your manifolds & risers, and you should feel good about that. A lot of people seem to start having problems as early as 3 years. My advice is take the risers as well as the manifolds off and throw them in a dumpster. Your luck is gonna change, and it will be a very costly mistatke, to the tune of several thousand dollars.

This is a "Do It Yourself" job without question, and would probably be in the neighborhood of $700.00 if you shop around on the Internet for the parts. Post any questions you have here on the THT before you get started, and you will be in excellent shape to handle the project.

[Brad1]

There was an article in Trailer Boats magazine a few years ago on this subject. In that article were listed some general life expectancies for exhaust manifolds, depending the envrionment they were used in. For warm saltwater, 3 years. For cold freshwater, it was something like 10 to 15 years. I think you can purchase the parts to do that project yourself for roughly 1/2 of the price you mentioned. If your planning on keeping the boat, you can spend the money you saved by doing it yourself, on a closed cooling system. Then you wouldn't have to worry about it any more.

[dwg2116]

Try rephrasing the question this way:

Should I replace my eight year old manifolds right now, by myself, at my conveinence in my driveway for $700, or should I wait a year or two when the total bill will be closer to $4000 because I need a mechanic and a new longblock too?

[markt111]

I lost a motor two years ago do do roughted manifolds, I would never let that happen again. New motor $4000.00, new manifolds to go with it $700.00 I used Osco manifolds fro local supplier