Re: Yanmar Exhaust Mixing Elbows

Since I just had a major engine failure on our Yanmar 3JH2-E where our exhaust mixing elbow became restricted and partially blocked, I want to help others prevent an engine failure like ours. There are currently two styles of Yanmar Mixing Elbows in use. One that is the shape of a "U" and one that is more of a cube. The newer and more expensive being the cube. (see pictures and PDF)

The older "U" shape uses a 2" exhaust pipe and the newer "cube" shape uses a 3" exhaust pipe. The older engines use 2" exhaust and the newer engines us 3" exhaust pipe. Yes, you can install a newer style mixing elbow on your older engine and then use a reducer to take it from the 3" to the 2" without needing to rebuild your exhaust. NO you cannot reduce a NEW Yanmar Engine 3" exhaust down to your old 2" exhaust because your new engine will not pass the needed back pressure testing to sign off on the new warranty.

So, in our situation, if we were to replace our Yanmar 3JH2-E with a new Yanmar 3JH5 then we would need to rebuild our 2" exhaust into the new 3" exhaust. If we replaced our engine with an exact replacement (which we chose to do) a 3JH2-E then we could keep our existing 2" exhaust and all other cables, shifters, mounts and items will fit right back into place.

This brings me back to the mixing elbow topic. What we have learned is that our engine failure, which must have been developing over many years, was primarily due to the increased back pressures caused by the ever closing mixing elbow old style. In 2008 we replaced this elbow, with a new one, at 2,450 engine hours. Then in Sept 2011, at 3,165 engine hours, (715 hours later) we removed the new mixing elbow and had it cleaned at a radiator shop. It looked fine. This now we know was a mistake. We should have replaced it at that time in 2011. You cannot really clean the mixing elbow. The build up in the mixing elbow is like concrete and it can NOT be cleaned out. At this same time, Sept 2011, we began our full-time cruising and our runs from MD to FL and the Bahamas. Over the next three years we ran back and forth to the Bahamas all the way from Maine to Long Island south of Georgetown, Exumas. On June 26, 2014 our engine failed at 4,650 hours, (1,485 hours after cleaning the elbow, and 2,200 hours are new) it failed from a spun connecting rod bearing on cylinder #3 only. No other failure.

Upon taking off the head and inspecting the valves, we found evidence of back pressure issues with lots of build up on the back side of the intake valves. You would think it would be in the exhaust valves but due to the back pressure, the exhaust is diverted to the intake valves and build up there. We also think our oil delivery system got blocked int he crankshaft at this one oil port for the bearing on connecting rod #3. All other bearings were perfect, so no evidence of low oil or lubrication. Just one bearing spun and welded to the this rod! Very odd.

So......in conclusion. If you have the OLD MIXING ELBOW style, like we have, and if you are running 300-500 hours a year in ocean saltwater, then I highly recommend that you REPLACE your mixing elbow every 3-5 years. I know I will be doing this with our remanufactured engine.

Here are some photos to help you identify the parts and the two styles.

Old Style Yanmar Mixing Elbow Part #7 Yanmar Part # 129198-13500 ELBOW, MIXING, about $200



New Style Yanmar Mixing Elbow Parth #15 Yanmar Part #129470-13541 ELBOW, WATER MIXING, about $900



Yanmar Mixing Elbow Part Numbers



Yanmar Mixing Elbow PDF file

WOW!!!! I just talked to Mack Boring in NJ asking about Neil Richards question. I found out THIS!!!! My engine, the Yanmar 3JH2-E came with a 3" exhaust! But, various boat builders asked to have it changed out to 2" so it would fit the boat better. So Mack Boring would take off the 3" and install the 2" mixing elbow! WHAT???? YUP! My next question was: How did a 3" exhaust engine pass the back pressure exhaust test with a new restricted 2" exhaust? He said....I don't know, but Yanmar must have signed off on it. Looks like Hayden Cochran will be investigating this a little bit more. Question. How many Yanmar 3JH2-E engines that had their original 3" exhaust mixing elbow removed and replaced with a reduced 2" exhaust mixing elbow fail? When did they fail? How many failed? We need David Juall Esq. To jump in here!!!!!

Thor
Thank you. We have maintained the mixing elbow replacing it in 2008 with new. Then 3 years later we once again pulled the heat exchanger tubes cleaned that as well. I guess our error was that in 2011, the 3 year old mixing elbow we inspected with it off and had it cleaned. It looked new and clear inside as far as we could see. I think the next 3 years of running MD to Bahamas loaded it up. We were scheduled to and planning on pulling it in Aug this year for replacement after the summer sail.

My current frustration is with this topic of 3" exhaust original on this 3JH2-E Yanmar and upon new, it was reduced to the 2" exhaust and this very poorly designed mixing elbow.

So Yanmar designed it with the $900 3" mixing elbow and then it was changed down to this 2". Something seems wrong with that design change.

I am not looking for a refund or anything like that. I just want to understand how a 3" exhaust design can be approved by Yanmar with a changed out 2" exhaust.

I know of many yanmar 3JH2-E engines that have failed. Could this topic be part of the reason towards failure?

What do you think??
Typos due to cell phone posting...

Here is the PDF specifications from Yanmar showing the Back Pressure specs and the recommended size of the exhaust is 2.5" Not sure what that means but please reference this PDF for all installation specs on the 3JH2e.





Here is the Exhaust as specified by Yanmar 64 mm = 2.51969"


These extra fittings that are threaded closed in our mixing elbows are used to thread in a back pressure testing meter. In order to have a new engine certified for warranty by Yanmar, the selling dealer needs to run the boat at a sea trial and test the back pressures at various RPMs. If the engine meets these pressure settings or below, then the engine can be certified for warranty.

SO....this still brings up the same question:

What are the back pressure results on a 3JH2e engine, designed for a 3" exhaust when a 2" exhaust is in place? Does the 3JH2E meet these specifications with a 2" exhaust?

Thor:
I replaced this mixing elbow with NEW in 2008. Then in 2011, I removed it and had it cleaned at a radiator shop, and yes painted it then as well. When it came out of the radiator shop it looked completely cleaned out inside, so I re-installed it. That was a mistake I see now.

Yes, in 2011, when we started our ocean runs, I should have replaced the then 3 year old mixing elbow, but I thought cleaning it was ok.

I agree, these old style mixing elbows, the 2" U shaped ones, need to be changed out every 3-4 years especially if you run in salty water.

Hayden

Don:
We are still waiting for the shipping in of the remanufactured engine from Schooner Bay Marina in WI. I am thinking it may ship the week of Aug 11.

Good idea on buying a new mixing elbow, I plan a new one every 3-4 years now! That is, if it is the U shaped one. Thanks for asking.

Hayden