I/O Exhaust Riser life in Fresh Water environment

[ejnichol]

What is the expected useful life I/O Exhaust Riser life in Fresh Water environment? I'm on my third I/Opowered boat and 99.9 % of there marine environment has been in fresh water lakes

We never replaced one but my previous boat, '95 Sea Ray with Mercruiser 5.7l Bravo 1 had results from oil test that indicated significant levels of water combustion by products in the oil. That engine was 23 yrs(650 hrs) old at time of test. So it was probably due to failing risers? Engine always ran well.

 

[alldodge]

In fresh it will probably outlast the boat. Pulled them off my 1994 during repower and they still look great

 

[garbageguy]

When we re-powered our 1998 model year, I cleaned and re-painted the exhaust risers on that 350 (I assume original), to put on the new 350. They looked fine, and have been good on the re-power engine for the 5 years it's been in the boat. I think this boat has always been in non-salt water.

 

[ejnichol]

Thats good to hear.

Our first boat back in early eighties had the 140 hp 4 cyl mercruiser with close to a 1000 hrs and we, my dad mostly, never even knew it was a thing to be concerned about. That was a tough motor/stern drive as we ran the crap out of it and did well to get oil changed.

Not sure why that 5.7l was showing sign of water in combustion unless it was a head gasket issue. I

 

[Lou C]

Water contamination can come from several causes, blow head gasket, rotted intake manifold (prob not likely in freshwater) even leaky manifold to elbow gaskets allowing water to leak back into cyls after shut down. Since this is the easiest to remedy I’d remove the manifolds and look to see if there are rust stains in the exhaust ports in both the manifolds and cylinder heads. If so then clean up the sealing surfaces make sure there are flat and level and reassemble. As far as other causes I’d warm the engine up remove the plugs and do a compression test; look forward rust on the spark plug electrodes that is often a sign of blown head gaskets. Does the motor oil look milky at all?

 

[ejnichol]

Water contamination can come from several causes, blow head gasket, rotted intake manifold (prob not likely in freshwater) even leaky manifold to elbow gaskets allowing water to leak back into cyls after shut down. Since this is the easiest to remedy I’d remove the manifolds and look to see if there are rust stains in the exhaust ports in both the manifolds and cylinder heads. If so then clean up the sealing surfaces make sure there are flat and level and reassemble. As far as other causes I’d warm the engine up remove the plugs and do a compression test; look forward rust on the spark plug electrodes that is often a sign of blown head gaskets. Does the motor oil look milky at all?

The oil always looked fine. I sold that boat about 3 years back now. It was running fine. If you ran it for extended period at WOT it had a very faint sounding crank knock afterward at low to idle rpm. Once it cooled down or ran at anything other than WOT rpm it didn't make a sound.

I think what your on to make sense. It was starting to get up in hours.

 

[Scott Danforth]

Not sure why that 5.7l was showing sign of water in combustion unless it was a head gasket issue. I

check the flappers and check the SWL height

if your boat is sitting too low, then a wave will push water into the exhaust manifold.

 

[Grub54891]

1983 140. never replaced the risers. Never touched most anything other than regular maintainence since I've owned it, 10 years.

 

[Bondo]

Ayuh,..... They'll last pretty much forever in freshwater,.....

Worst I've ever seen, were easily fixed by flat filin' the manifold/ riser gasket surfaces,....

 

[QBhoy]

Hi. Answer is a long time. But also depends where you are too. Here in Scotland, it’s been known for exclusively fresh water boats to require them replaced after a while. I had a boat that needed them done after about 18 years. In those days, it wasn’t common to leave antifreeze in engines over winter. The climate here is particularly bad for varying conditions day to day over winter. Common for corrosion to happen over winter if they are left empty and damp for months. My friends scarab just had to do his this year on his 7.4 mercruiser. They lasted 31 years !
Long story short…they last ages…but not forever in some climates and not protected over winter ! Even fresh water only boats.

 

[Lou C]

All fresh water is not the same, some can be pretty corrosive, as Merc found out with the early B-IIIs that didn't have enough anodes to offset the stainless props.

 

[alldodge]

Corrosion on a B3 is not increased by water, is caused by the added stainless props when boats are on shore power. Needs increase in current from mercathode and additional anodes to protect