Last month I replaced the mixing elbow on my three cylinder Yanmar. A mechanic had told me that they are generally suspect after 10 years. My engine is 13 years old and has around 1800 hours on it. It was an easy job taking both the elbow and the exhaust adapter off (4 bolts, see photo). Although the engine still seemed to put out a good flow of water and I did not experience smoking exhaust, an inspection of the point at which the water and exhaust mix (see second photo) look like the inside of a cave and appear to be about 50% restricted. If your engine is of similar age, it might be worth a look. It can be inspected by loosening the aqua lift, removing the connecting hose, and viewing the inside with the help of a mirror. I am very happy that I performed this bit of preventative maintenance.
Im due for this service myself, and want to get it done before I set sail again. I was told this is actually more like a 3-5 year replacement part. I do have low water flow, so I’m sure I’m VERY ready for replacement.
Did you buy all three pieces together? I’m just starting to source the parts… if you have any suggestions, I’m all ears.
Ben,
I think I bought each piece separately, but all from the same Yanmar parts supplier. Don’t forget the gasket and I was told to remember to put some sort of anti-seizing compound on the threads to make the next time easier. Geez, was it 2007 I did this?
Wayne
Ben,
The top casting is the part that deteriorates–I’ve replaced ours twice in 22 yrs (5000 hrs). From the start, I had an extention welded into the pipe which raises the top casting about 10". The extension was done at a marine exhaust shop and the pipe has held up fine. I have a mild steel brace between the bottom of the top casting and the lifting strap on engine to control vibration. I’ve replaced the lower casting once, about 5 yrs ago.
Dan
Update:
This winter, Shaula’s exhaust has become noticably more “smokey”–probably due to unburned diesel, as there was a bit of a sheen on the water nearby. The compression checked out fine. The injectors were checked and re-nozzled. The exhaust was still “smokey”. Two mechanics suggested I check out the exhaust mixing elbow. Although I had replaced the upper casting about 7 yrs ago, when I checked it out, it was very restricted-looking–lots of carbon and rust.
Instead of replacing the mixing elbow casting, I took the advice of my mechanics, and took it to a local marine exhaust shop that supports both the commercial fishing fleet, and the pleasure craft folks. They welded up a stainless replacement of the upper casting. They have done this for many Yanmars. See the picture. As already mentioned, the ss pipe was lengthened back in 1988. To match the old height, the vertical pipe was lengthened a bit more and the 180 degree turn welded on. The Yanmar casting is “jacketed”, resulting in the injected cooling water keeps the casting cool. This new ss weldment will get hot from the exhaust gases, and needs to be wraped with fiberglass tape, which I’ve now done.
I was delighted to find that the exhaust “smoke” and the sheen are gone!
Dan BCC #59
Managed a quick trip to the boat in Florida a couple of weeks ago, and was in consult with a good friend of mine a diesel mechanic who came over and had a look at the boat. He knew about my exhaust troubles a couple of years ago and had a quick look. His first comment was why was the water injection intake for the exhaust cooling on the side closest to the engine instead of on the other side away from the engine. I replied that I thought there was no thread to accommodate the vertical pipe on one side of the mixing 180 degree pipe. I thought his comment had some value, any comment from anyone? I note that the great job Dan did with his custom fab, put the mixing water away from the engine which may well be prudent.
Of course I could be dead wrong and there are threads on both side of the mixing 180 pipe, in which case maybe I should reverse and then reconnect the exhaust hose. See images above from Odyssey and then from Dan. Any wisdom?
Hello Stewart - the standard Yanmar 180 degree mixing elbow has the nipple for water injection on the engine-side of the 180 degree turn. However, the water is being injected into a water jacket, and mixing with exhaust gas does not occur until the other side of the 180 degree turn - the side farthest away from the engine. I suppose it is possible that should corrosion produce a leak in the jacket allowing water into the exhaust channel on the engine-side of the 180 degree turn, that you could introduce water into the engine while cranking without successfully starting. This elbow is cast iron - and should be regarded as a maintenenance item that needs to be replaced every few years. On my old engine, I used to fabricate the elbow from standard galvanized pipe - avaialble anywhere.
Calypso’ old engine was a SABB G engine. Iduna is also fitted with a SABB G engine. On our engine, the water is injected into the exhaust inside a large complex casting called a silencer. Jeremy’s fabricated elbow was connected to the silencer. Perhaps, Jeremy will clarify that point.
Stewart,
As Jeremy says, the top Yanmar casting has an inner passage that pushes the cooling water over the top before it joins the exhaust gases. Wayne’s picture at the beginning of the thread shows the openings in the casting where the gases and water come together. The pic shows the corrosion that results from hot salt water and exhaust gases on cast iron. I’m guessing that the corrosion buildup eventually constricts the passages, resulting in backpressure. After 3or4 years, if the casting looks like Wayne’s, it’s probably time to replace it.
Dan Shaula
excellent thanks very much guys, that clarifies it all, I really do appreciate the forum and the meeting of minds, it is just great an arena to air all manner of things form technical to emotional…
A question to the group. Is the cause of the 3gm30F’s mixing elbow occlusion mainly carbon buildup or iron corrosion? Having recently replaced mine,I reasoned this: If the main cause is iron corrosion, then a bronze mixing elbow may extend the life of the elbow significantly. Carbon buildup, on the other hand, would occur no matter what the elbow was made of. I asked Port Townsend if they made one before. Pete said no, and the cost, once they were tooled up, would be $200-250. But tooling up is expensive, so there would have to be other interest for it to be profitable.
If I’m not mistaken, Yanmar puts a bronze elbow on one or more of their later model diesels.
What is the thinking on this among the engineers and engine experts in the forum??
Hello dwkayaks.
Perhaps I was a little verbose. Simply put, would making the mixing elbow out of bronze, instead of the current cast iron , improve the its life span?
Patrick
sv Nereus
Patrick,
The Beta exhaust elbow and the one the marine exhaust shop made for me are both made out of stainless, so avoiding cast iron. Cast iron and cast bronze both result in weight that’s not so good if the elbow is raised up some (as the Beta and my custom one do). It seems like easily corroded cast iron is a poor material for a mixing elbow. I think that any water jacketed casting, with it’s hard to inspect passages, is poor design, maintenance-wise.
You could probably have a custom bronze elbow welded up, but the threads on the bottom of the vertical pipe might be a challenge (or the weldment could eliminate the lower casting?). I don’t know how much better a bronze weldment would be than a ss weldment.
Dan Shaula
Hi Dan,
thanks for the response. I got the impression that Pete at Port Townsend foundery could exactly duplicate the Yanmar mixing elbow for the 3gm30f in bronze. It seems that the stainless coupling that connects the mixing elbow to the manifold wouldn’t be adversely affected with bronze compared to cast iron.The question remains that if bronze is used, would much of the corrosion problems encountered with the cast iron be ameliorated or totally prevented with bronze?
Gee , Dustiniii , that is very definately a Good Question !
I did look up the throat of my “choaked” exhaust elbow, upon removal .
The corrosion build up was Iron - Rust and very solid, not flakey stuff !
I banged on it with hammer and cold chisel, but the build-up was as solid as the iron casting, itself !
Maybe a caustic acid could be used, to remove that Rust deposit , I just don’t know .
We will just have to let the “Brains” on this Forum , have a go , at this problem , in the mean time , a spare Yanmar exhaust elbow is in the parts locker.
