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!!!!!

Hayden as per Mastry engine center St Pete FL the exhaust elbow should be changed out every 3 to 5 years, Down in SW FLA. in the water 365 a year , in 3 years it is ready for changing. Not that it looks like it from the outside About $125. Should it corrode through internally salt water may make its way into the engine via the exhaust, not good at all. Careful left hand threads on the elbow. Changed mine last week. A good time to remove the heat exchanger for cleaning new o rings and gaskets, a very few bucks more and easy with the elbow out. A gallon of new quality coolant after hosing out the water jacket where the exchanger was. Put it all back,Check for leaks and go sailing.
Sorry for your problems, perhaps these postings can save others from a very costly breakdown. Bet many sailors are past due for this easy preventive maintenance.
Fair winds
Thor

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...

Hayden
I think that for a few bucks savings and 900 is not a few we would get a 2in exhaust or even an 1.5 if it would work.
Thor

We had the same problem with our Packet Cat. Ater one year of service the SB engine was burning substantially more oil than the PS. We had our Yanmar mechanic search for clues, did a compression test, etc., no problem found. Eventually Mastery Engines said they would look into the problem under warranty, but we had to get the engine to them (Mack Boring would look at the engine but would charge for their services). After some time, and cost, no known solution was relayed to me but the engine was reinstalled in the boat. Oil consumption was fine. I was interested in learning the cause and was told only thet "the engine showed signs of running hot". Nothing more was said, no further problem. We sold the PC with 4000 hours on the engines. Speaking with the new owners learned that after their second season they needed to rebuild the SB engine, details unknown. My understanding is that it is now, maybe not back then, that due to "modifications" at the factory Yanmars in IPs ran hot. My final point is that if you change the mixing elbow to a 3" and retain the remaining 2" exhaust, I do not believe you will get the full advantage of the 3" modification. You are still pushing into 2" pipes. My $.02.