Yanmar manual mixing elbow maintenance

Gunni · Jun 30, 2016

I saw that too, and no I do not. Last year at 600 hrs I removed the exhaust discharge hose and inspected the elbow, light coat of carbon black. I do follow Yanmar instructions to minimize engine idling, make sure to run it up to 3000 rpm prior to shut down, and give it a 4 HR run every month, even if I have to motor sail it. My elbow is more like a 120deg welded stainless fitting, not the tighter 90deg cast iron loop.

Roland5048 · Jun 30, 2016

Have a Yanmar 3YM20. Replaced the U-shaped elbow in Jan. after just over 500 hours. Made a noticeable difference in performance. I idle very little and only when necessary and always let engine cool a bit and rev over 3000 rpms several times before shutting down to clear any soot and carbon. Even with that, elbow still had a little soot and carbon build-up. While captaining a charter vessel several years ago, (charter vessels are notorious for lack of maintenance), had a blocked elbow completely shut down the motor as we were approaching a bridge. Fortunately, we were able to turn around and get the sails up in time. Well spent $$ for piece of mind and better performance.

ddrewry · Jun 30, 2016

Has anyone tried these? I came across a guy on ebay who make the mixing elbow and exhaust pieces from stainless. They look really good compared to the stock yanmar parts and cheaper too. I'm thinking or ordering both, just curious if anyone has a first hand report?
http://www.ebay.com/itm/231870851928?_trksid=p2060353.m1438.l2649&ssPageName=STRK:MEBIDX:IT
http://www.ebay.com/itm/231908004581?_trksid=p2060353.m1438.l2649&ssPageName=STRK:MEBIDX:IT

whatfiero · Jun 30, 2016

So far so good on the stainless ones I'll let ya know in winter how clogged up as I check mine every winter and clean the cast one is always clogged up and I changed every 5 yr

ddrewry · Jun 30, 2016

I recently bought a Hunter 37.5 and initially thought the black stuff under the rear mattress and the engine compartment was some kind of mold... I've since discovered it is actually exhaust from the Yanmar 3HM35F... what a mess!
I'm looking to replace the whole exhaust system clear to the thru hull. There are other signs the older gentleman didn't keep up with maintenance like he should have but I've never seen anything like this. Not ready to condemn the Yanmar yet...but that's a lot of soot...

the_alpine · Jun 30, 2016

Those stainless ebay elbows are intriguing. I've replaced my mixing elbow 2 times in 5 years. Engine is starting to feel like its ready for the 3rd (losing a small amount of rpm). It really is pretty silly that the oem parts are cast iron.

mz4wheeler · Jun 30, 2016

Why would the material (SS vs Iron) make any difference to the carbon buildup? Wouldn't both get equally clogged?

NYSail · Jun 30, 2016

mz4wheeler said:
Why would the material (SS vs Iron) make any difference to the carbon buildup? Wouldn't both get equally clogged?

Agree...... Soot build up will happen I would assume when you have dirty hot exhaust hitting cold water. But would imagine the SS part would clean easier without the flaking. Maybe next time I change I will try one...

the_alpine · Jun 30, 2016

My experience is that the cast iron degrades and weakens inside the elbow.

Maybe SS would do the same?

Allan12210 · Jun 30, 2016

I will be interested in seeing the reports on how long those SS elbows last. Typically, SS does poorly in an extremely hot/humid environment. There were some for sale earlier with wall thicknesses that were quite thin compared to the OEM cast iron. They might erode through quickly. The latest ones I see on e-bay seem beefier. In my case, the coupling (left and right hand threaded piece) that joined the two cast parts together is what failed. It just snapped off flush with the portion that bolts to the engine. That coupling was made of SS. Prior to that I never disassembled the parts but I would give the innards a good scrubbing with a wire brush. It lasted 26 years.

rardiH36 · Jul 1, 2016

The first attached photo is of the second Yanmar cast iron OEM elbow that I had replaced on my 2QM20. The first one failed the same way. The second probably had only 200 hours on it... but 4-5 years and say ~150 outings. I discovered the crack after not using my boat for 6-7 months (wasn't a good idea to go sailing while recovering from a broken neck). I suspect that the cause of the failure might be that a puddle of raw (sea) water would remain in the elbow's "bulge" each time the engine was shut off.

This time I did replace with a stainless steel elbow. Rather than through the eBay portal, I bought it direct from www.exhaustelbows.com. (Ben, the proprietor and craftsman/maker of the elbows was a good resource during a couple of email exchanges. He dispatched the elbow on the same day I placed my order. On opposite coasts, I had it two days later.)

I have also attached a photo of my SS steel elbow installation. It's only been about 5 months now since I purchased. So too early to determine how it will do over the long term. But this replacement has a straight run down to the exhaust hose. No bulge to allow the "puddle" raw water to remain between engine uses. The price seemed right and worth the experiment ... even though I also had seen some posts that SS might not do well for exhaust elbow duty. Looks very pretty though!

Warren Milberg · Jul 1, 2016

Last year I helped a friend change out the mixing elbow on his 1986 Yanmar 2GM20f. This was the original elbow with no known maintenance done on it for the past 29 years. We believe the engine had between 3000-4000 hours on it. Amazingly, the engine still ran. My guess is my friend will up his maintenance schedule on the new elbow.

mz4wheeler · Jul 1, 2016

rardiH36 said:
The first attached photo is of the second Yanmar cast iron OEM elbow that I had replaced on my 2QM20. The first one failed the same way. The second probably had only 200 hours on it... but 4-5 years and say ~150 outings.

Correct me if I am wrong, but I always thought the purpose of water injection into the elbow is to *COOL* the exhaust components, because the engine is in an enclosed space. If not properly cooled, one of the results will be an extremely *HOT* engine compartment. In looking at your two photos, the water injection is several inches back from the exhaust manifold on the SS elbow, which would leave a HOT SPOT, and a failure to adequately cool the exhaust manifold, compared to the OEM elbow. My prediction is that even though it looks pretty, this will lead to early failure of a much more costly exhaust manifold and valves, and a very hot engine compartment. Additionally, this will also lead to early failure of other engine components like hoses, motor mounts and alternator. etc.

My take is yanmar designed the elbow to operate in extreme environments (i.e. a closed compartment). Deviating too much from the original design is asking for trouble. I don't know why your's cracked. Perhaps the angle of installation was incorrect to allow sufficient drainage.

rardiH36 · Jul 1, 2016

MZ4Wheeler:

Good observation. And I will investigate the next time I'm at my boat. However, from memory, I think that the area around my exhaust manifold is anti-freeze cooled. Also consider the other Yanmar GM20 type configuration with the elbow "pre" fitting going vertically up after the exhaust manifold. Then the cooling sea water isn't injected until the downward 180 degree bend. So probably about the same distance in inches of the elbow "assembly" that isn't directly cooled by the seawater injection.

After returning to the berth a couple of times, I actually have felt with my hand how hot the new SS elbow is between the manifold and the injection point. I didn't burn myself! And so far, the SS piping between the seawater injection and the manifold has not heat distressed discolored at all. So probably not attaining critically hot temperature.

Might be a few days, but I will report back!

Anyway, the picture of the OEM cast iron elbow in my previous post shows a pretty extreme type of failure, I think. I saw no soot/carbon build-up inside the OEM elbow. It was caustic salt water vs. cast iron.

Gunni · Jul 1, 2016

These are double-wall mixing elbows. Heat is not a problem.

Tally Ho · Jul 1, 2016

mz4wheeler said:
Correct me if I am wrong, but I always thought the purpose of water injection into the elbow is to *COOL* the exhaust components, because the engine is in an enclosed space. If not properly cooled, one of the results will be an extremely *HOT* engine compartment. In looking at your two photos, the water injection is several inches back from the exhaust manifold on the SS elbow, which would leave a HOT SPOT, and a failure to adequately cool the exhaust manifold, compared to the OEM elbow. My prediction is that even though it looks pretty, this will lead to early failure of a much more costly exhaust manifold and valves, and a very hot engine compartment. Additionally, this will also lead to early failure of other engine components like hoses, motor mounts and alternator. etc.

My take is yanmar designed the elbow to operate in extreme environments (i.e. a closed compartment). Deviating too much from the original design is asking for trouble. I don't know why your's cracked. Perhaps the angle of installation was incorrect to allow sufficient drainage.

I always assumed it was to cool the exhaust gases so they would not melt the rubber exhaust hose.

Greg

ddrewry · Jul 1, 2016

yep, cools the exhaust - many mufflers downstream are actually plastic. engine cooling is a different loop whether raw water or fresh water cooled

Johnb · Nov 21, 2016

OK, I am in the process of changing out my mixing elbow on my 3QM30 - should I go for Yanmar original or stainless steel?

Yanmar manual mixing elbow maintenance

.

.

.

.

.

.

.

.

.

.

.

.

.

Attachments

.

Attachments

.

.

.

.

.

.