Exhaust mixing elbow on Yanmar 4JH4-HTE (Turbo)

[drapem1]

I have the “Optional” U shaped mixing elbow on my yanmar 4jh4-hte which is attached to the turbocharger. i have just over 1000 hrs on engine and not sure that this elbow has been cleaned or replaced. the yanmar manual shows the elbow type (approx 120 degree bend) and doesn’t provide any additional information or service recommendations for the larger U shaped type elbow (see attached pic)
I have read the many forum threads on exhaust mixing elbows and understand that based on yanmar (replace at 500 hrs or two years) but from the many responses from forums, it’s best to replace with new elbow, although the time and hours varies greatly from the forum replies.
My question is really more about this particular elbow type. Would there be a different recommendation on service and replacement for this type? It’s clearly more substantial than the other stock model type and much more expensive! There have been no noticeable problems either visually or in engine performance degradation. Would it be advisable to at least remove and inspect? Hoping to get more life but also don’t like to push any part past it recommended service life.
Any experienced opinions very much welcomed.
Thank you!

[Peter Brookes]

Hi. We had the same elbow fitted to our Yanmar. At 2500 hours I removed the elbow and cleaned it out. There was some carbon buildup but nothing too significant. There was no sign of any erosion or corrosion, and I would expect this optional elbow to last for up to 10,000 hours subject to periodic cleaning, and following Yanmar instructions to periodically operate engine at wide open throttle to blow any loose carbon out of the engine.
You will see that it is possible to immerse the elbow in a strong alkali cleaning solution to remove the carbon. Although effective this is likely to reduce the life of the elbow as it will result in erosion of the casting. I advise you remove the blanking plugs and scrape out with a long narrow screwdriver, but unless you are blowing any black smoke from the exhaust I would not expect this needs doing for another 1000 hours or so. Have a new gasket available for re-fitting the elbow.

[Bruce Beard]

I had one of these on a 3JH4E that plugged up.
It really fooled me because I’d occasionally remove it and inspect it. The blockage can be found on the output side where the cooling water is injected into the exhaust stream. I’d been looking at the other side thinking there was nothing wrong.
In the end, mine lasted some 7 or so years and 1500 engine hours before I began noticing soot on the transom. When I finally figured out where it was clogging it was down to a hole smaller than my little finger!
Pull it off and turn it upside down then look back into it, you may be surprised!