Yanmar Exhaust Elbow

[Gunni]

Nick;

• You are definitely running your engine too slow. These are not your grandaddy's lugger diesels, they are modern, high compression, high-speed diesels. You should be running your Yanmar above 2500 RPM. There are Yanmar service bulletins that specify this, and it is described by Yanmar as the quickest way to shorten the life of your engine without running it out of oil.
• Running a Yanmar at lower speeds is a well-documented way to cause carbon build up and coking in the mixing elbow. You may be saving a few shillings on fuel, but you are creating expensive problems.
• My stainless steel mixing elbow is 12 years old, clean, no cracks, no corrosion. That is real world, not some guy talking about what he heard from some guy. My engine cruise speed is always 2,600 RPM and even at 2.0 liter burns 0.75 gal./hr.
• I have seen mixing elbows look like yours in short order - the elbow carbons-up, water flow restricts, temperature soars and the seawater boils off, creating massive and fast scale and corrosion. Meanwhile, upstream in your engine, you have reduced power and overheating. Given the long history - likely lots of carbon too.

 

[nick8489]

Seems like the ells are killed by the sea water cooling.. at the lower loads, the exhaust is a lot cooler and the water cooled ell walls will condense out some nasty tars.. There is proportionally a lot more excess air in the exhaust at low loads, which can help with salt and metallic salt deposition. It takes a while for this stuff to consolidate, so if ya power up for 10 minutes or so before you shut down (increase gas velocity and temperature).. you can help make the ell last longer. You won't see this problem in land applications because the comparatively thin exhaust system runs at much higher temperatures. You can convert to a hot exhaust as was in some boats (Catalina 27 comes to mind), but having a 600+ degree pipe running through the boat is not desirable. I agree about the engine mounts.. It seems that Yanmar could have chosen a different elastomer or design that could have preserved the elastic properties and lasted a lot longer.

Good info Kloudie- thanks

 

[nick8489]

Nick; [*]You are definitely running your engine too slow. These are not your grandaddy's lugger diesels, they are modern, high compression, high-speed diesels. You should be running your Yanmar above 2500 RPM. There are Yanmar service bulletins that specify this, and it is described by Yanmar as the quickest way to shorten the life of your engine without running it out of oil. [*]Running a Yanmar at lower speeds is a well-documented way to cause carbon build up and coking in the mixing elbow. You may be saving a few shillings on fuel, but you are creating expensive problems. [*]My stainless steel mixing elbow is 12 years old, clean, no cracks, no corrosion. That is real world, not some guy talking about what he heard from some guy. My engine cruise speed is always 2,600 RPM and even at 2.0 liter burns 0.75 gal./hr. [*]I have seen mixing elbows look like yours in short order - the elbow carbons-up, water flow restricts, temperature soars and the seawater boils off, creating massive and fast scale and corrosion. Meanwhile, upstream in your engine, you have reduced power and overheating. Given the long history - likely lots of carbon too.

Thanks Gunni
Good info