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Yanmar 3YM30 - Still need a High Rise exhaust mixing elbow?


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We have 2 x Yanmar 3YM30 in our cat and I'm due to replace the stupid yanmar exhaust mixing elbows that seem to last only a few years. I'm looking at the HDI ones rather than the Yanmar one as I hear good things about them.

We currently have the high-rise mixer style but I don't think we need them anymore as we have changed the rest of the exhaust system. 

Original Exhaust system :

  • High Riser Mixer (no anti syphon fitted. Mixer head is about 150mm above waterline)
  • Wetbox in bilge
  • Exhaust hose then looped up about 300mm above waterline
  • Hose ran down to outlet about 100mm above waterline
  • Marked as pink on pic below

I was nervous out how low the loop was, so I changed the system to (new loop in green on pic below):

  • High Riser Mixer (no anti syphon fitted. Mixer head is about 150mm above waterline)
  • Wetbox in bilge
  • Exhaust house then loops up about 1000mm above waterline via another muffler (only really used at a 180 degree bend). Marked as green on pics below.
  • Exit via the existing outlet 100mm above the waterline

I think I no longer need the high rise mixer style as the high looped exhaust stops the risk of anywater coming back up the outlet. I will need a anti syphon device to stop water coming via the water feed. The normal elbow mixers are half the price and half the parts to corrode, so It would be nice to change it I can. 

What do you think?

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Much as I dont like the inefficient shape (gas flow wise) of the high rise, I would be hesitant in going to the older lower style -I run a 3YM30AE as well. What you have done aft is a good move, but the crucial points to observe are maximum drop to the waterlock from the injection elbow-and volume of the waterlock -it has to take every drop from the high point of your new loops and dripping from the elbow once shut down, without any heading back up towards the engine. These points are of course common to all yacht engines, and yes before someone asks typically the exhaust hose is 1/3 water on shutdown. 

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