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Old 29-11-2017, 03:18   #1
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Mixing Elbow on Yanmar 3GM

Morning, all. This question may have been asked here before now, but if so I didn't find it in the threads, so here it is:

The engine on the sailboat Sequoyah is a 1999 Yanmar 3GM30F. It has a cast U mixing elbow, high rise, 2" outlet, 5/8" raw water inlet, mounted on a cast riser (manifold) protruding off the upper stern end of the motor. The riser is attached to the engine with four machine screws, or bolts. I understand this is a standard configuration for this engine at the time it was made. I don't know, yet, what material the elbow or the riser are made of. Iron, bronze, stainless? The elbow has the original Yanmar silver gray paint on it, never cracked at the joints. The engine itself has only 300 hours of operation, so that isn't surprising.

I'll find out just what it is and whether or not it's stopped up next week when I remove it, but I think there's a good chance the elbow is clogged with soot or corrosion. I am not getting proper cooling for the motor, and after a quarter hour of operation warmth starts backing up into the raw water hose leading from the pump to the exchanger, as I think it shouldn't. If so, I may be able to clean this elbow, but given its age that may not be the anticipation I ought to have here.

I hear Yanmar no longer use this design. I can get a direct replacement, affordably for cast iron, unaffordably for cast stainless steel. I also can get a reasonably priced mixer of a different, nonrising design from Exhaust Elbows, fabricated of stainless steel tubing. Replacing this OEM mixer with that one would eliminate the high rise. I even have heard of people who have built their own no rise mixers from iron pipe, which strikes me as a cheap solution that would probably require more frequent replacement but that might work.

My question is this: Is it important to keep that rise? Is the purpose of it to prevent water from flowing back to the engine when the boat is under sail and heeling sharply? Have Yanmar indeed abandoned the high rise design on newer engines, and if so why? Did it not work out in practice, or am I mistaken in my thougth they no longer prefer it? In short, would there be a danger were I to switch out the old elbow and riser for one of the Exhaust Elbow products?
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Old 29-11-2017, 04:15   #2
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Re: Mixing Elbow on Yanmar 3GM

The first time mine clogged on my previous Pearson, I wire cleaned the water inlet. Worked a while and I replaced it with a new Yanmar elbow of a straighter design. Worked until I sold the boat 8 years later.
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Old 29-11-2017, 04:18   #3
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Re: Mixing Elbow on Yanmar 3GM

By a straighter design, do you mean an elbow that's hardly an "elbow" atall, that bends downward from where it bolts onto the engine? That's the one that outfit I mentioned (Exhaust Elbows, I think its name is) appears to sell to replace the Yanmar U style.
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Old 29-11-2017, 04:54   #4
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Re: Mixing Elbow on Yanmar 3GM

Yes. It was a tube, just over 2, that angled down from a welded flange that bolted on. The water entered from a smaller tube welded to the bigger tube. Worked fine.
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Old 29-11-2017, 04:59   #5
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Re: Mixing Elbow on Yanmar 3GM

That's exactly the experienced information I'm seeking. Thank you.
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Old 29-11-2017, 08:15   #6
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Re: Mixing Elbow on Yanmar 3GM

I have a friend that got a replacement mixing elbow, exhaust bend, and union for about $100 for his 3GM. Please PM me and I will forward his information.
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Old 29-11-2017, 08:20   #7
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Re: Mixing Elbow on Yanmar 3GM

I've got the same engine 3GM30. A couple of years ago, I discovered that my elbow was cracked one day. When trying remove it to inspect, the whole thing just disintegrated in my pipe wrench. I ended up having to unbolt from the engine and replace both the elbow and the flange.

I bought a new one online - the extra cost for Stainless wasn't that much. Here's an example. https://www.ebay.com/i/332234575202. $155

On an extended trip, I would probably buy an extra one ahead of time and keep with my "spare parts".

~markb
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Old 29-11-2017, 08:37   #8
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Re: Mixing Elbow on Yanmar 3GM

The one on your boat is cast iron, both the exhaust elbow and mixing elbow.

The best solution for your engine is the cast 316L SS parts for sale on ebay by HDI Marine from a materials point of view.

The SS tube solution is a flawed design and the cast iron solution is subject to corrosion blockage of the raw water flow which is what you are currently experiencing.

Mixing elbows are not the item you want to try and save a few dollars.
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Old 29-11-2017, 08:38   #9
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Re: Mixing Elbow on Yanmar 3GM

FYI:

The pipe threads on a Yanmar exhaust are Japanese / British Standard.

Nipples and fittings are available from McMaster-Carr.

You may need a taller nipple between the manifold and mixing elbow to put it above the waterline as required to prevent a back-siphon, water in the cylinders, and a BROKEN engine.

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Old 29-11-2017, 08:49   #10
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Re: Mixing Elbow on Yanmar 3GM

The elbows do require cleaning every 300-500 ish hours Maybe 700 hours the first time. I used a bike spoke, pushed into the water passage from both ends, to rod out the water passage. The gas side also gets gunked up with carbon. For that I used a 1/4" dog chain run through the elbow and run back and forth to de carbon it. Gives another 300-500 hours that way.

There are cast iron elbows on ebay for $109 and SS for $155. I purchased mine off ebay from a Canadian manufacturer. Mine had a threaded plug to gain access to the water passage.

BTW getting the threads loose off the old elbow was way too much fun. For me hours of fun, but it did finally come undone.
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Old 29-11-2017, 08:53   #11
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Re: Mixing Elbow on Yanmar 3GM

I'd go with cast iron over SS. They corrode less in that environment IME.
Keep the riser design, unless you can figure out it's not critical to preventing flooding your engine!
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Old 29-11-2017, 09:50   #12
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Re: Mixing Elbow on Yanmar 3GM

Yanmar has two types of mixers. The type that you need is determined by the location of the exhaust manifold in relation to the surface of the water outside. If the engine is mounted low in the hull, in other words, the deeper loop is necessary to prevent water backing up. If the engine is mounted where the exhaust is above the waterline, the shallow angle pipe is used.
Extra deep engines even have extensions to raise the loop higher, as a siphon break.
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Old 29-11-2017, 10:13   #13
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Re: Mixing Elbow on Yanmar 3GM

The exhaust port on Sequoyah is under the overhanging stern, not at all far above the waterline. A following sea would put it below the surface. So would hard heel to starboard. The engine itself is mounted partially below waterline. From the comments, that must be why Yanmar, or Hunter who built the boat, went to the expense of installing the rising mixer. Sounds as if I ought to stick with it.

So, the first job is to remove, inspect and try to clean the old iron one. Even if I can do that successfully, it's beginning to look as if I should get a spare to keep aboard. Iron that old can't be in the best of shape now.

Cheechako recommends iron over stainless steel for this application. I've come across comments elsewhere saying that SS requires the presence of oxygen to form a corrosion-resistant surface layer, there isn't enough inside the mixing elbow to do it, and therefore iron does indeed work better. Any thoughts on that?
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Old 29-11-2017, 10:17   #14
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Re: Mixing Elbow on Yanmar 3GM

Quote:
Originally Posted by Cheechako View Post
I'd go with cast iron over SS. They corrode less in that environment IME.
Keep the riser design, unless you can figure out it's not critical to preventing flooding your engine!
I'm surprised to hear you feel cast iron is better in that application. I've used both and have found that the SS model flows much better over time. The raw water passage on the cast iron mixing elbow can corrode fairly quickly. Short of crevice corrosion, the 316L casting offers superior flow.

Materials aside, Yanmar's design of the mixing elbow is terrible. The water injection point is designed in such a way that any corrosion or crack on the dry side could easily drain back into the exhaust manifold.

Any engine that uses a short riser (which assumes below working water level installation) such as the one the OP has should always install a siphon break as high as possible. Just my 2 cents.
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Old 29-11-2017, 10:30   #15
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Re: Mixing Elbow on Yanmar 3GM

When I'm referred to the SS model I meant specifically the cast SS model that's a direct replacement for the Yanmar part.

Not the welded SS tube fabrication. If not done in 316L schedule 10 pipe, TIG welded and passivated, then I agree cast iron is better.
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