On two different boats with different diesels (Yanmar and Universal) at about 25 years ... the cast iron exhaust elbows have rusted through...
1st symptom is "blistering" on the outside of the cast iron or partial small cracks with rust. You see the same kind of blistering on cast iron water pumps used in pools or fountains.
I'm thinking those cast iron parts just need to be changed every 25 years whether they look bad or not.
dirty sooty exhaust in cabin is very distracting. you really don't realize just how dirty boat diesel exhaust is from these engines until it fills the cabin. And instead of pushing the cooling water out it overfills the bilge. Your first thought is that the boat is burning ... but no ... just blowing "carbonized" water into the engine compartment.
