I removed for inspection the exhaust mixing elbow on my Yanmar 3YM20. I was glad I did. It was heavily corroded on the inside and the iron was extensively deteriorated. The engine is 9 years old and runs in cold, salt water.
We have a band saw at my work, when the blade is needs replacement, I will run it through to show how bad it is and post a pic. If a mixing elbow rots right through it can spill raw water back into the exhaust manifold and wreck the engine. I decided to try a 316 stainless aftermarket elbow mad by HDI marine, available on their website. I was a little hesitant, I usually spend the extra and go OEM, plus I've had a few disappointments with aftermarket parts online. I'm happy with the quality of the part, it's a close to exact match to the original Yanmar one, except the HDI doesn't have the oddly placed frost plug the Yanmar has (the frost plug is at the very top, which means the elbow would have to be nearly full of water when it freezes for it to pop...?). It's a nice casting, lots of weight and the interior of it looks very good quality. Too bad the did straight BSP instead of NPT threads on both the water inlet and exhaust outlet. The Groco "full flow' 1 1/4" pipe to 1 1/2" hose barb fitting isn't available in BSP. I assembled it with a good dose of nickel anti-seize for stainless, and will make it a point of disassembling it annually for inspection. Pictures: https://photos.app.goo.gl/RnNuMKzVZrFbjNKS7 Eric
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