Mixing elbow (yes, another one) Yanmar 3YM20

Roland5048 · Dec 10, 2022

I have the exact same issue. Installed a brand new 3YM20 in '08. Mixing elbow replaced about 300 hours ago. Mechanic who installed the engine hopefully coming next week for an unrelated issue and to do the recommended 1000 hour check up. Will report back what I find out. Hopefully, it turns out to be a non issue.

Roland5048 · Dec 10, 2022

OEM replacement. Am taking a serious look at the SS replacement.

MikeHoncho · Dec 10, 2022

If your able to confirm it was replaced in 2020, I would be more concerned about overheating than the rust. In this case the surface rust is a symptom of the elbow overheating. Not a big issue for the elbow but is for the downstream exhaust hose or worse, the engine not getting water. Confirm you have adequate flow to the elbow. I had the elbow with the raw water hose attached and hat threads into the exhaust hose plugged with scale and rust which caused this issue.

Ralph Johnstone · Dec 10, 2022

Thanks @vandiver for your excellent photos and full description. Lately, this site has become a magnet for idiots who give the minimum possible information on a problem and never any photos. Yours lacks nothing.

In spite of your excellent presentation, I'm scratching my head as to why the corrosion pattern looks like it does. This is what's inside an old cast iron elbow I sectioned :

As you can see, the interior of the elbow is not suitable to painting once cleaned.

vandiver said:
Was thinking initially into dissasembling, checking inside, cleaning it and painting it to extend its life, but really would lean towards having a more definitive solution.

Your area of corrosion appears to originate just above the "dam" in the elbow:

I had a leak in one of four mixing elbows I've replaced in the past and it was in this same spot that leakage occurred. In mine, the exterior appeared as a single pin hole with a rust stain dropping down from it.

The corrosion pattern is somewhat different in yours :

...................... and you have another area on the elbow outlet which looks unusual. Maybe there's nothing out of the ordinary here other than your corrosion is occurring over a larger surface area on the inside. Maybe clean it up to get a better idea of what's going on inside there ?

Have you checked the temperature of your mixing elbow when you've been running full throttle for a good hour ? It should be slightly cool to the touch on the top surface and warm on the bottom.

vandiver said:
Have been reading a lot in the forum about it and everything points to an overall recommendation that I should buy and HDI Marine replacement kit, guess also that the full assembly with U-Shape and the elbow part is the highest recommended option once I need to dissamble the existing one to check status.

I installed an HDI SS mixing elbow three years ago and still haven't made up my mind on it. I'll be pulling it tomorrow for another internal scoping and have a better idea on it then.

If you do go for an SS elbow, you will only need the elbow :

You will not require part #11 as it hasn't seen the effects of CO2 and water which are a killer. Consider getting part#10 as it seems to weaken after a few years of running. Part #16, always good to have a few extra around.

I know you know this but :

Cheers

markwbird · Dec 10, 2022

Odd that it is rusting on the outside. is it painted?

MikeHoncho · Dec 10, 2022

vandiver said:
Apparently not painted…

Or was and it was burnt off.

Ralph Johnstone · Dec 10, 2022

vandiver said:
if there is something else in top that is not working well, if that’s the case could you please indicate what the root cause might be?

You could have something like this and not know it :

Although this one did not leak. Just because it's plugged is not the cause of corrosion. It had an opening of about 3/8" through the deposited carbon but the engine ran fine. I have no idea why my engine deposited carbon this badly when it didn't smoke and was in top notch running condition for 2900 RPM running.

I think you'll find a leak in the elbow wall at the point indicated I indicated in post #6. A good scrub with wet/dry emery on the outside may give you a better idea of what's going on. Also, try to get a good look for carbon buildup in the discharge side of the elbow when you pull it off. That, and also let us know how the temperature test works out.

Getting all the gasket material off the two flange faces will be the mother of all creation depending on your access to the elbow. Once it comes to the re-install, this may help :

This shows the gasket slathered in parting compound :

.............. which ensures the gasket falls off the next time the riser (part #11) is removed. The studs are temporary to guide the riser on to the discharge manifold. As each stud is removed, an original bolt is inserted.

Same goes for the 2" OD elbow discharge where it fits into the 2" ID hose. Only in this case use a NON petroleum grease such as SuperLube :

................. and slather a lot into the hose to keep it from sticking next time.

vandiver said:
I think I will purchase the st st version to be ready in case I will need to replace the elbow,

You very likely will be replacing the old CI elbow. May as well as the HDI SS elbow costs 1/2 the price of a Yanmar CI elbow, at least in this part of the world. They do have a very interesting property in that they do not collect carbon deposits for whatever reason :

This is the CDI SS elbow after 2 years and about 200 hrs. of running. The soot you can see is easily wiped off with a rag.

The carbon deposits in the picture of the sectioned Yanmar CI elbow have the consistency of diamond and require charges of C-4 explosive to budge them. That's why I recommended not trying to paint the interior of the elbow.

vandiver said:
will do the temperature test as you recommend to check if there is something else in top that is not working well, if that’s the case could you please indicate what the root cause might be?

Are you referring to high gas temperature due to a lack of cooling raw water through the heat exchanger ? If so, let's wait for the results of the temp. test before going there.

Ralph Johnstone · Dec 10, 2022

vandiver said:
Apparently not painted…

Something's rotten here for an elbow purchased (I presume) and installed in 2020. Never seen a Yanmar mixing elbow that was not painted. Got to wonder how this one was not painted.

MikeHoncho said:
Or was and it was burnt off.

My thoughts originally but :

....................... notice how the riser below the engine has not been burned and the 90° elbow going into the mixing elbow has not lost its paint either. And the 90° elbow is made of brass and would conduct the heat quickly. The mixing elbow lost its paint very evenly if it was burned off. Just looks like general rust on unpainted CI.

So many questions, so little time

!

Tin Kicker · Dec 11, 2022

Never thought about it before but the hot gas flow around the top is terrible from an engineering standpoint and answers why the hot corroded spot appears on the outside. The hot gasses plus particulate don't just flow up from the left and before being forced to do a 180 down to the right. The left side above the threads is redirecting them toward the finger between the two sides which has been eroded away. The particulate is being directed toward the cooler wall the water is coming through, so of course the gunk will collect there.

And after too long this develops between that hot spot, back along the hot path through the thinnest part of the wall, and into the stress imposed on the mounting threads.

I just replaced mine with the same stainless elbow and consider it a consumable.

MikeHoncho · Dec 11, 2022

Ralph Johnstone said:
Something's rotten here for an elbow purchased (I presume) and installed in 2020. Never seen a Yanmar mixing elbow that was not painted. Got to wonder how this one was not painted.

My thoughts originally but :

View attachment 211540

....................... notice how the riser below the engine has not been burned and the 90° elbow going into the mixing elbow has not lost its paint either. And the 90° elbow is made of brass and would conduct the heat quickly. The mixing elbow lost its paint very evenly if it was burned off. Just looks like general rust on unpainted CI.

So many questions, so little time !

The tight change of direction of the exhaust has allows the latent heat in it to conduct to the area. It’s heat related . Look at the rusts outline on the side. The area is the exhaust passage. Above it is where the water injects. .

Roland5048 · Dec 18, 2022

Reporting back. See my post #2. Mechanic found the elbow to be about 98% blocked. Sent me pics via e-mail. Said the salt in the water crystalizes under the high heat and corrodes the elbow from the inside out. Replaced with an OEM. Mech said he didn't see any benefit to the SS given the higher cost. I mentioned having thought it might be the injectors based on what others had told me. He then told me not to take advice from those who know not what they are talking about. Mech replied that in his many decades of servicing Yanmars he never once had an issue with the injectors or fuel pump on the YM series. In fact, he said they were practically bullet proof. This mech installed my motor, 3YM20, in '08 and is considered to be the Yanmar guru in this area. Went and cranked her yesterday and after a bunch of spitting and coughing, she started right up, threw a crap load of black smoke and soot out the exhaust before clearing up and running like it was right out of the box.

In retrospect, this is something I could have done myself but consider the price of admission worth it rather than blindly going down the injector rabbit hole.
I have the tools and know just enough to be dangerous...to my wallet, that is. :facepalm:

Ralph Johnstone · Dec 18, 2022

Roland5048 said:
He then told me not to take advice from those who know not what they are talking about.

He sure hit that nail squarely on the head.

Roland5048 said:
In retrospect, this is something I could have done myself but consider the price of admission worth it rather than blindly going down the injector rabbit hole.

Ignoring the fact that the injector idea was a bad idea at best, it's always best to work from inexpensive to expensive solutions when you're just trying out ideas. The mixing elbow replacement would have been the cheaper experiment at that point.

Looking at a few of your numbers here :

Roland5048 said:
Mixing elbow replaced about 300 hours ago.

Roland5048 said:
Mechanic found the elbow to be about 98% blocked.

If your elbow went from new to 98% plugged in 300, you've got some bad :poop:

going on in there. My elbows were lasting about 6 - 8 years (600 - 800 hours) between replacements.

One idea that "MAY" be worth trying (because it's free) to reduce the coking in the elbow is every boating season, try to run your engine at the continuous rating output (below is for my 2GM20f) for at least an hour to clean up your piston rings. Sorry, I don't have the continuous rating for your 3YM20. Do this twice during the season.

Before getting into this habit, every time I opened up the engine above 80%, I could smell the odour of burning oil in the exhaust. No smoke however. The oil smell would be gone after about 20-30 minutes. I then got into the habit of opening up to 3400 RPM for an hour maybe twice in the season. After that, going from 2800 to 3400 did not produce any smell of burning oil.

I haven't been doing this long enough to affect anything in the mixing elbow but carrying partially burned oil through the elbow can't be improving the coking situation any.

Roland5048 · Dec 18, 2022

For the first 19 1/2 years I owned this boat she was berthed 3 miles up river in brackish water. So 3 miles back from the gulf in brackish water. More so on an out going current. Never had an issue. Really never had to have a diver to clean the bottom. The last 6 1/2 yrs. I have been up a 2 mile no wake zone on a dead end canal leading right to the gulf. Need a diver now. I always thought I was being prudent in opening her up when I left the no wake zone and before the trip back. Obviously not enough. Need to start running her a bit harder although I always try for 80% WOT and WOT when I can. Live and learn. At least not too many boat bucks.

MikeHoncho · Dec 19, 2022

2 year old elbow that is 98% clogged and your guru mechanic says to just replace it? With a “cheaper” Yanmar over a SS? The title guru is subjective…….

Roland5048 · Dec 19, 2022

MikeHoncho said:
2 year old elbow that is 98% clogged and your guru mechanic says to just replace it? With a “cheaper” Yanmar over a SS? The title guru is subjective…….

That 2 yr. old elbow came out of the OPs boat. See post #1. Mine was at least seven years old. Replaced during my last bottom job. I trust this mech. Any other mech could have raked me over the coals with any number of bogus things that they claimed were in need of replacement. It may be that this mech is just my guru but, trust is important.

Mixing elbow (yes, another one) Yanmar 3YM20

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