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Discussion Starter #1
I have a Yanmar 3GM30F engine with 2,500 hours on it. It starts cold on the first crank and runs like a champ, but I have noticed that recently I can't get it to run at revs higher than 2,700 RPM. I have started eliminating possible problems (air filter, fuel filters) and now I will try replacing the mixing elbow. The model of mixing elbow is this one:

Yanmar Mixing Elbow 128370 13550 FOR 3GM30 | eBay

I know that mixing elbows can slowly get clogged with carbon buildup, especially the "U"-shaped ones, and restrict exhaust outflow, preventing the engine from getting up to full revs. The model of mixing elbow I have is a gentle angle (45%?) with a welded pipe on top for the cooling water to enter the exhaust. It doesn't seem that carbon would have a chance to build up in this elbow. Is that the case? I want to change it anyway as the welds are getting rusty and I know it's on its last legs (it's the original one that came with the engine).

Has anyone had carbon buildup problems with this model of mixing elbow?
 

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Discussion Starter #3
JSaronson, have you got the same engine and mixing elbow? I'm loath to remove it before I have the new part (and gaskets) to replace it. I will certainly check for carbon buildup when it's off.
 

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Mark.. I'm guessing it has little to do with shape.. the hot gases hitting the colder water probably precipitates material over time in any case.. (but just guessing ;))
 
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Thanks Ron. I'm rather hoping to find the elbow clogged with carbon. Then I'll know I've found the problem. I'll find out when it's off. I know the U-shaped Yanmar elbow is prone to buildup, but the one I have just seems to have such a straight run that I can't see how it gets clogged. If anyone has the same elbow, I'd love to hear about clogging.
 

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soak in vinegar and do some vingear flushes of the intake and let it sit for a while

does wonders

edit I had the 2gmf, I think the elbows are the same...not sure though:)
 
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I had it in my old boat. Yanmar recommends changing it out every 250 hours or get it cleaned at a radiator shop. The mixing elbow in this model is very prone to carbon blockage. Also the water inlet to the mixing elbow is famous for getting clogged first.
One way to know is the exhaust smoke starts to get white at running speeds.
 

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before removing put the inlet in a vinegar bucket...start engine and completely suck all the vinegar till it starts coming out...

let sit for at least 24 hours...sometimes up to 48

then flush with distilled water(cold)

if this DOESNT help you must dismantle and manually clean

this shoud be done as regular maintenance and you save a lot of money versus buying industrial engine "cleaners"

I did this on my last engine an atomic 4 and the difference in max loaded rpm was very noticeable

power loss and parasitic loads can come from many sources on an engine, fuel, air, cooling system, belt chafe...etc...
 
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Seems cleaning would be a lot cheaper than replacing. I would pull it and if you see any carbon on it, take to a radiator shop and ask them to "boil it out." (not sure what the Portuguese term would be as they don't really boil it) They generally have baths of really strong chemicals that they can dip it into and it will clean it to bare metal. You should be good to go for several more years after that.
 

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yup shops "boil them" if its cheap to do won there like here I would do that...however you can do the rest yourself using vinegar...
 

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Discussion Starter #12
Thanks for the tips everyone. I still plan on replacing the elbow because the welds look a little rusty and it is probably time anyway (2,500 hours). I'll clean up the old elbow and put it in the "spares" kit.
 

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now thats some smart thinking, fix your current stuff to act as working spares...kind of a sailors motto
 
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Yanmar Mix Elbow

I started to see a lot of black/brown soot when revving by motor so it determined it could be 1 or 2 things:

  1. Injectors were becoming clogged and therefore needed to be pulled and cleaned or
  2. Exhaust elbow was clogged with soot.

At first I was not looking forward to pull the whole exhaust portion of the motor off, but it is super simple and can be done in about 15 min if easy access. Disconnect the cooling water hose from the mixing elbow and then disconnect the whole piece of the exhaust manifold (mixing and exhaust elbows) from the motor by removing the 4 bolts.

I took mine home, separated the exhaust elbow from the mixing elbow, removed as much scale as I could with flat head screw driver, then soaked the both pieces overnight in vinegar.

Thoroughly rinsed and check flow through each with a stream of water. Reassembled, put on a new exhaust gasket and then put everything back together.

Fired up motor and black/brown smoke was gone.

My elbow is original to the motor, 1992, but my motor only has 700 h.
 

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Hi All (even though it's 3 years since the last post!).
I have a Yanmar 3GMD and recently noticed a deterioration in engine performance. There was a lot of black smoke and occasionally, a black inky trail in the water. Eventually, it worsened to the point that, 2 weeks ago it would only idle.

It turned out that the outlet from the exhaust manifold was completely clogged to the point that I don't understand how the engine ran at all - let alone how the black smoke even made it out of the exhaust.

It wasn't just blocked with carbon - there was a hard rust formation which had, over time, almost completely clogged it.

I took off the manifold and cleared out the offending port and brought the part to a local machine shop to have the flange face refinished.

In my case the elbow isn't an elbow at all but just a short pipe with a flange which connects to the exhaust manifold block (with gasket in between).

Once all reassembled the engine ran like a dream. It had been slowly choked to death by an ever decreasing means of exhalation. From now on it's now on my list of things to check every 2 years.

BTW the engine is 32 years old and I suspect this had never been looked at previously!

Chris.
 

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Hi Daniel,
In my case it was the exhaust manifold port that was completely blocked. The pipe connecting to it (with the coolant water inlet) was fine. I'm not sure why this was the case.

See photos (1) as it was when I first discovered it and (2) after cleaning out and refinishing the flange.

Chris.
 

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Daniel - Norsea 27
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Hi Daniel,
In my case it was the exhaust manifold port that was completely blocked. The pipe connecting to it (with the coolant water inlet) was fine. I'm not sure why this was the case.

See photos (1) as it was when I first discovered it and (2) after cleaning out and refinishing the flange.

Chris.
:eek
Wow! that's ugly.
Odd that the pipe was fine, but seeing that the manifold was blocked, maybe the pipe was installed while there was still an opening in the manifold and just not cleaned out by a previous owner.... Just "thinking out loud".

But really good that you fixed that. Could have caused much more problems.

Just shows that engine maintenance goes beyond changing oil and filters. :wink

With all the work I did to my engine, I'm thinking a regular inspection of the head and cooling passages is a good idea too.
Good job, Chris!
 

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Hey Daniel.
That's a good theory. It's not possible to see the exhaust port when you take off the "elbow" pipe (or 45 degree pipe in my case). You can only see into the pipe you've just removed. The last time someone possibly looked at this was in the days before smart phones - with cameras - allowed you see around corners and make videos of out-of-the-way places in your engine. This is what I did to discover the ugly truth behind my fading engine!

Thanks for your comments!

Chris.
 

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Hello,
This thread seems as close to what my issue is as anything, without starting a new one (how does one do that anyway?)
Has anyone seen this happen to your yanmar 3ym30 exhaust manifold/elbow (inverted U shaped)? My engine is 3 years old(Feb 2014 install) has only 200 hrs on it. The boat has been hauled out every year by the beginning of a hurricane season and saltwater cooling flushed out with fresh water religiously, every time, once on the hard. Then I would disconnect the exhaust hose and stuff a piece of rag/cloth into the elbow exit and cover with plastic and secure it with a rubber band so no water or salty air gets blown into the manifold. (After removal, the rag did not look soiled or wet).
What you see in the pictures is salt crystals mixed with something resembling a very fine white powder (aluminum oxidation?). Mechanic that did the installation is as befuddled as I am. To create so much deposit one must evaporate quite an amount of saltwater.
Does that section need a yearly maintenance? Have not seen that being mentioned in the service/user manual.

Any ideas/help in identifying what and how that might have happened are greatly appreciated.
 

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