Re: Yanmar 2QM15: How can I keep it running forever?
The elbow isn't the real problem as far as longevity of your engine...the real problem will likely be the exhaust manifold. You can buy a new elbow and it won't cost you an arm and a leg. Mine cost about a hundred bucks...if I remember correctly...when I bought it about five years ago.
The exhaust manifold on the other hand is a weak link due to hard scale fouling and relatively thin walls that are subject to corrosion and it has a pretty significant thermal stress due to the temperature difference between the exhaust and cooling. And you can't buy one. If yours fails internally you either have to scavenge one off an old engine if you can find one or have one built. I seem to remember reading about someone having one built a few years ago but I don't remember the details. Would certainly be more expensive than replacing the exhaust elbow.
Another problem area for you if you have the 45 degree elbow rather than the U-shaped elbow may be the transition piece that the elbow screws into on the aft end of the manifold. When my elbow rusted out I was unable to get the elbow out of the transition piece and I had to replace that piece as well. I don't think it is available anymore.