www.iFourWinns.com

Glad to hear that, the water in the exhaust is the bane of inboards and even affects some outboards like the 4 stroke Yamahas that have exhaust corrosion issues.
To be on the safe side, look at your risers at 5 years. The dry joint is much better at not leaking at the joint between the mani and riser. You can put on a new riser then or just re-do the whole system. But I would not go over 7-8 years on cast iron manifolds.
Try doing what I have done:
if you winterize, after draining fill your manifolds with marine AF that has corrosion inhibitors in it. I do think that it helps, because when I start it up in the spring, I don't see rusty water, only clear water coming out.
Doing an oil analysis is a good idea but its kinda like getting certain medical tests at a certain age, everyone agrees its a good idea but it might tell you what you don't want to know lol. However, it could save the engine, and save money in the long run.

_________________
88 Four Winns 200 Horizon
4.3 OMC Cobra-4bbl
2002 Walker Bay 10/2012 Suzuki 2.5
2008 Walker Bay 8

1998 Jeep Grand Cherokee 4.0/Selectrac
2007 Jeep Grand Cherokee 5.7 Hemi/Quadradrive II

great information in this thread!
My 1998 Sundowner 195 with a 4.3 V6 has about 400 hours on it, all freshwater use, to my knowledge the exhaust manifolds/risers have never been off, the marina that has been winterizing my boat just blew out all the water after draining it, this year I did it with the 100F antifreeze as recommended here, but to my knowledge it has sat all winter without any liquid most of it's life.
since it has been a freshwater boat do I still run the risk of manifold failure?
If I pull the riser off will I see something obvious?
When I pull it out in the spring I want to correct anything before I have to get towed back to the dock , nothing more embarrassing than sitting out in the middle of a lake doing SOS signals!
thanks for any info...
Bob

Hi Sled guy,

Others on this forum with far more experience that me may offer more precise info, but in my experience there's three main points of "failure" due to corrosion in manifolds and risers/elbow.

1) The joint where the riser bolts onto the manifold. There are usually water channels that allow water to flow through the joint from the manifolds into the risers. Because there's a joint (and a gasket) at this point, corrosion can occur and water can start leaking into the exhaust manifold, and into the cylinders when the engine is turned off (Note: later model mercruisers and some other engines moved to a "dry-joint" design which did away with water channels across the joint and fed water seperately to the manifolds and the risers to try and eliminate this potential point of failure). To inspect this you need to seperate the riser and manifold.

2) The exhaust elbow where the rubber exhaust pipe coupling connects to the riser. Water is sprayed from the elbow into the exhaust through small holes near this connection point which is supposed to keep the rubber exhaust pipe (and the internal "flapper") cool. These can corrode to the point where water wil fall back down into the riser and manifold rather than out the exhaust when the engine is turned off. To inspect this you need to remove the rubber exhaust coupling from the riser.

3) Corrosion of the exhaust manifold casting. Usually internally at the joint to the engine block. Or cracking due to heat stress, (usually on the underside of the manifold and tends to happen when the internal water channels start to corrode and become blocked, causing uneven heat spots in the manifolds). To inspect you have to pull off the manifolds.


These are the three most common causes I'm aware of but there are other problems that can also cause failures. Best advice is to take them apart and inspect every 5 or so years (maybe less often if it's a trailer boat only used in fresh water and winterised properly).

This is a good article on the subject http://www.boatus.com/seaworthy/swbtob.asp

_________________
2005 Sundowner 205

5.0L MPI Mercruiser, Bravo1, 3 blade Mirage SS prop

good advice and nice article, for peace of mind I will pull the manifolds & risers in the spring! thanks!!

Don't forget that if you are removing them, if you want to remove the risers first to check before removing the heavy manifolds, drain them. Reason being that when you break the seal on the riser then if there is still water in there or even antifreeze if you use it to winterize it will run down the center exhaust passage and into a cylinder via an open exhaust valve.
If you have no rust on the outside of the joint between the riser and manifold I bet that you have no issues but it is still a good idea to at least check the joint. You want to make sure that there is no deterioration in the sealing surface on the manifold and riser. It is only about 1/4th in wide. This is why the Merc dry joint is superior to the system that Volvo still uses.

Reports that I have heard from fresh water regions indicate that their manifolds can last almost indefinitely. However, because you can have leaks simply from a bad gasket, then it makes sense to drain and check em, even though the likelihood of them rusting out is slim. Post up pix of what they look like when you do it. If you see no flaking rust in the cooling passages then no worries. Here's what a set of OMC one piece "Batwing" manifolds looked like after 5.5 seasons in the salt on my 4.3....

https://www.dropbox.com/s/co8mqd4vi8qze ... w.jpg?dl=0

Notice one of the cooling ports was totally clogged with rust. I was able to clean these out and they can be reused for a few more seasons. The thing is that you never know how close you are to the wall of the water passage rusting through, but you can test them by filling them (carefully!!) with acetone. Acetone has lower surface tension than water and will find cracks and holes that water won't yet pass through.

I'm guessing that yours in freshwater will look like the new one on the left...lol....

_________________
88 Four Winns 200 Horizon
4.3 OMC Cobra-4bbl
2002 Walker Bay 10/2012 Suzuki 2.5
2008 Walker Bay 8

1998 Jeep Grand Cherokee 4.0/Selectrac
2007 Jeep Grand Cherokee 5.7 Hemi/Quadradrive II

At 17-18 years old now, if your going to pull them to inspect, I would just spend the $650 or so to replace them. But if you have time, then by all means...pull them and post pictures. Then we can give a better opinion.

_________________

"Knot Easy" 2000 Horizon 240 Volvo 5.7GS /SX
tow: 2017 Honda PILOT EXL-AWD
prev. boats:
'87 Chaparral 198CXL 4.3 OMC Cobra
'69 Jetstar 16ft Ski Boat, 115hp Yamaha
'68 Aluminum Jon Boat, 3hp Sears
'64 Water Wings