[C320-list] Yanmar 3GM30F Exhaust Elbow/Riser

[Dennis Cookson]

I am thinking about replacing, or at least inspecting, the exhaust elbow on our 1999 Yanmar 3GM30F as its age and condition are unknown. It seems to be a non-standard construction, unlike any Yanmar part I can find, with a U-shaped riser which is fully insulated with a woven thermal sleeve of unknown material, possibly fibreglass.

I’ve uploaded a photo of this elbow/riser <https://c320.org/mediagallery/media.php?f=0&sort=0&s=20210324212234253> to the Technical Photos gallery.

It roughly resembles the shape of the “Exhaust Riser C-320”  on the Catalina Direct web site which I see is made of stainless steel. The raw water inlet to this riser is located well away from the exhaust manifold, on the downhill side of the ‘U’ close to the connection to the rubber hose that leads to the waterlift.  The fact that the riser has to be insulated makes me wonder if the water is actually used to cool the pipe, i.e. is it essentially a dry riser where water is not used for cooling but just for reducing exhaust noise.  In this case, perhaps there is less risk of a failure causing water to enter the 

I’d be grateful for any advice or information re the following questions:

- is this part prone to catastrophic failure from internal corrosion, in the same way that the original Yanmar mixing elbows are?  Anyone had that experience?
- what lifetime in terms of age or engine hours can reasonably be expected?
- if it needs to be replaced, must it be replaced with a similar custom part like the one on Catalina Direct, or it is ok to use the Yanmar 128370-13610 Mixing Elbow Riser Kit? This has a much tighter bend with water input very close to the manifold.  (I’m assuming that the riser needs to reach a specific height above the water level at all angles of heel - this arrangement would be more compact.)

Dennis Cookson
Catalina #577