Mercruiser 4.3 Manifolds & Risers - how to check them?

[SandyBoat]

My 2002 boat has a Mercruiser 4.3 EFI motor with the Alpha Gen 2 outdrive. The engine has around 300 hours use on it, all of which has been in saltwater and normally flushed with fresh water after use.

Now I know that the exhausts have a finite lifespan on them and failure can be catastrophic, but is it possible to remove the risers and the manifolds and inspect them to determine if they need to be replaced? Obviously I would rather replace them than risk destroying the engine, but don't want to change anything unneccesarily.

I have searched for information on this, but can't seem to find anything definitive, so any thoughts would be welcome.

 

[zbnutcase]

Re: Mercruiser 4.3 Manifolds & Risers - how to check them?

There is no definitive answer because every situation is different. However, at going on 8yrs and 300hrs of saltwater, I would have to say your about due for replacement; I would do it if it was my boat. 'nutcase

 

[Don S]

Re: Mercruiser 4.3 Manifolds & Risers - how to check them?

Manifolds and risers usually fail in 2 ways. They start corroding inside and the rust fills the passages and the engine starts running warmer, usually noticed by an engine that normally runs at 170? running at 175? to 180? consistantly.
That's when they should be replaced.
THe other failure is actually easier to notice. You start the engine and it's only running on 4 or 5 cylinders till it runs for a while and clears out. This is where people loose an engine is it's sitting with salt water in it. What happens is the gasket surface area of the exhaust manifold and riser corrode away and allow water to leak from the water section of the manifold to the exhaust port and enters the cylinder through an open valve. If that gasket surface is thin or turned into a black carbon substance, it will leak.

 

[SandyBoat]

Re: Mercruiser 4.3 Manifolds & Risers - how to check them?

However, at going on 8yrs and 300hrs of saltwater, I would have to say your about due for replacement;

That is really what I was thinking. I don't want to do nothing and risk destroying the engine.

Don; thanks for the information and the picture, exactly what I wanted to know. Right now the engine is running fine, with no noticeable change in temperature and as smooth as it ever was. When the weather improves a little I will take the risers off and have a look at the surfaces and then take it from there.

Thanks again for the help.

 

[nofuss]

Re: Mercruiser 4.3 Manifolds & Risers - how to check them?

There is no definitive answer because every situation is different. However, at going on 8yrs and 300hrs of saltwater, I would have to say your about due for replacement; I would do it if it was my boat. 'nutcase

Ok I have a 2000 regal with 2X4.3 v6 with 300hrs each, run in mostly fresh water, i purchased the boat used and do not have exact history.

I got the boat running and found that the power was a bit low. however they ran at 160 degrees and idled fine. went out to the bay one day on return only one engine would start. got in did some checks and found water on spark plug.
removed the manifolds all failed a pressure test. Both engines. So my advice is cheap insurance, I may have been lucky, God sometimes protects fools. but i would change them out just as a matter of course. imagine if they failed.
If i had the knowledge i have now, i would have changed them before i ever ran the boat

P still No Fuss