Dom, I've followed your posts and knowledge for the time I've been on this site and regard your input highly. But I'll have to disagree on the aftermarket manifold issue ONLY when referring to Sierra parts, Osco parts are a joke and any other stock replacement manifolds do not have the casting quality that Sierra or OEM parts do. The photo I have posted is stock OEM Mercruiser quality after 3 years, saltwater use, obvious riser to manifold gasket leak. I've installed literally hundreads of Sierra exhaust manifolds and risers on Mercruiser engines and had NO failures. There is a specific method to installing any manifold and riser which I'll go over here.
WAboating, over time (3-5 years) the joint where the exhaust manifold and riser meet will end up leaking water through the gasket into the engine and possibly hydro-lock the motor. Even Mercruiser's new dry-joint exhaust will deteriorate through the water passage as it's a very thin casting (we're replacing a 6.2 that had this problem). The issue with manifold and riser replacement is not a backflow prevention issue, but rather now that entire section of cast iron has been exposed to not just moisture, but water, then air, then time sitting...that adds up to casting failure/gasket failure and then engine failure.
It is extremely important to remove ALL paint from the gasket mating surfaces on both the exhaust manifold AND the exhaust riser in order to have the gasket seat correctly. Many Mercruiser engines from the factory have not had this done and thus have had premature gasket failure between the manifolds and risers. DO NOT USE SILICONE on these gaskets either, they have a bonding layer which adheres to the casting once it sees heat.
The picture shows the surface of the manifold I'm talking about with part of the paint removed using a flat razor blade.
BTW, there was a class action lawsuit filed against Mercruiser by Sea Ray owners regarding exhaust water reversion in which the settlement statement from Mercruiser requires risers to be changed every 18 months in order to keep their warranty.
WAboating, over time (3-5 years) the joint where the exhaust manifold and riser meet will end up leaking water through the gasket into the engine and possibly hydro-lock the motor. Even Mercruiser's new dry-joint exhaust will deteriorate through the water passage as it's a very thin casting (we're replacing a 6.2 that had this problem). The issue with manifold and riser replacement is not a backflow prevention issue, but rather now that entire section of cast iron has been exposed to not just moisture, but water, then air, then time sitting...that adds up to casting failure/gasket failure and then engine failure.
It is extremely important to remove ALL paint from the gasket mating surfaces on both the exhaust manifold AND the exhaust riser in order to have the gasket seat correctly. Many Mercruiser engines from the factory have not had this done and thus have had premature gasket failure between the manifolds and risers. DO NOT USE SILICONE on these gaskets either, they have a bonding layer which adheres to the casting once it sees heat.
The picture shows the surface of the manifold I'm talking about with part of the paint removed using a flat razor blade.
BTW, there was a class action lawsuit filed against Mercruiser by Sea Ray owners regarding exhaust water reversion in which the settlement statement from Mercruiser requires risers to be changed every 18 months in order to keep their warranty.
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