Originally Posted by Doug Doty
I am a plastics guy of 35 years but even still I can only apply my experiences and use them to logically speculate as to the answer.
I am more curious why we have not seen internal coatings that prevent corrosion and make these components last as if they were made from stainless steel.
Beginning in the late 90's Mercruiser started using a ceramic coating on certain cast iron manifolds and risers. More recently, they developed a 'dry-joint' between the manifold and riser, which eliminated the most frequent failure point in the system. Recently some aftermarket suppliers started offering 'e-coating' in some of their replacement systems. This is supposed to be almost as good as the factory ceramic coating at a considerable cost savings.
Either way, these later coated systems last longer than the original painted cast iron components.
It would be interesting to find out if the earlier engines can be upgraded with the newer ceramic components and dry-joints when replacing the entire systems.
Before my trawler Boomarang, I owned and restored a classic Donzi 22 and learned more about Mercruiser exhaust than I ever wanted to.
Great subject Art and Doug.