Please explain manifold and riser failure to me.

[Fordiesel69]

I am talking about fresh water boats that HAVE been winterized correctly each year. Explain how these parts still commonly fail. I understand that salt water eats them alive as with any metal. But I am not seeing how fresh water destroys them in 10-15 yrs with proper maintance at 100-150 hours per season.

I assume the manifolds and riser material is about as thick as portions of the engine block, yet seldom do you hear of those rotting out.

Many of the boats I have looked at in the 1980's have original manifolds and I hear this is not a good thing as they are on borrowed time. My bayliner for example is a 1990, so the factory manifold are now 20 yrs old. Time for replacement even though no leaks?

 

[haulnazz15]

Re: Please explain manifold and riser failure to me.

Well it's not usually the walls of the riser/manifold that are the problem. It's the mating surfaces/gaskets in between the riser and manifold that end up failing. When these gaskets fail, or the small water passages corrode and leak into the exhaust, it ends up letting water pour into the exhaust manifold. Once in the exhaust manifold it goes straight into the combustion chamber where it can hydrolock an engine.

That being said, we were on the original manifolds on our 1976, and ended up with water in a cylinder which sat and rusted. This basically ruined the block for a rebuild and caused a lot of extra expense over a simply inspection.

Normally all you have to do is pull the risers, inspect the water passages, and reinstall with new gaskets and you're good to go.

 

[Jeepster04]

Re: Please explain manifold and riser failure to me.

Our boat is also a 1990 with the original risers+gaskets. Ive been thinking about taking them off and replacing the gaskets but Ive got that 'if its not broke dont fix it' saying going through my head. Worried we may not get the gasket just right and then it will start to leak. Is it hard to get the gasket lined up or do you just lay the gasket there then thread the bolts in and the bolts hold it in place?

 

[45Auto]

Re: Please explain manifold and riser failure to me.

If you stay with the "if it's not broke don't fix it" mentality on periodic maintenance and checks, expect at some future date to be where Haulnazz was - replacing the entire engine block.

The gaskets are easy to replace, clean up the surface and they just lay there. Risers can also fail from internal clogging which is hard to detect, which will overheat your engine.

 

[Fordiesel69]

Re: Please explain manifold and riser failure to me.

So all that is required is removing, resurfacing, and replacing gaskets on lets say a 5 year basis and it should be good? Sounds too simple to be true.