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Old 27-12-2010, 06:07   #1
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Exhaust Mixing Elbow Life

How long should you expect your mixing elbow to last? I've read lots of cruiser blogs and have seen a fair number of mixing elbow replacements in them. A friend recently got a fairly new boat and it needs a new elbow and he seems to think 7 years is as long as you can expect 1 to last. Near as I can tell my 22 year old Cal has it's orginal elbow after 2000 hours of engine run time.

Should a mixing elbow be considered an important spare part to stock on the boat for a long trip?
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Old 27-12-2010, 06:18   #2
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Seems that with gas engines, cast iron elbows tend to last 5-7 years. On diesel, as you experienced much longer which may be due to the size of the water injection openings to control the greater heat created by the exhaust. When I had to replace 20 yr old cast elbows (2200 hrs) on my Perkins 6.354, I went with cupronickel fabricated by Marine Manifolds in Long Island, NY. Will probably outlast me . With 2000 hrs I would certainly consider having a replacement aboard as insurance, as in my opinion, you are about at the end of the useful lifespan of your elbow.
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Old 27-12-2010, 06:34   #3
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On my old Volvo diesel, I've had the following experience with exhasut elbows, for what it's worth:

original custom stainless steel, brackish water: 10 years/700 hours
Mild steel pipe, salt water: 2 years/1000 hours
Bronze fittings, brass pipe, salt water: 4 -5 years/1500 hours
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Old 27-12-2010, 06:48   #4
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Quote:
Originally Posted by Don Lucas View Post
How long should you expect your mixing elbow to last? I've read lots of cruiser blogs and have seen a fair number of mixing elbow replacements in them. A friend recently got a fairly new boat and it needs a new elbow and he seems to think 7 years is as long as you can expect 1 to last. Near as I can tell my 22 year old Cal has it's orginal elbow after 2000 hours of engine run time.

Should a mixing elbow be considered an important spare part to stock on the boat for a long trip?
Our Westerbeke has 3200 hours on the original and I had it off last winter to re-paint the manifold. I inspected it and re-used it because it was fine, even at 3200 hours of use. One thing that always sticks out to me is that boats I have fixed that have pre-mature exhaust elbow failures are almost always over-pitched/propped.

When I used to survey with a buddy of mine we always compared max rated engine RPM to actual during sea trials. The boats that were off always had owners that had a history of exhaust elbow replacements and this was another observation that backs up my first.

That being said cast iron exhaust elbows will fail sooner than aluminum ones, regardless of prop sizing. In my experience this type of failure is more age & rust related than soot/cake related but I suspect that soot/cake only adds to the speed of deterioration.

I have also suspected that many of the failures had a role played by high sulfur content fuel, which we no longer have in diesel fuel. From my observations I have seen the cake layer inside the elbow retain moisture when the engine is shut off. This moisture laden layer of soot/cake could be another cause of slab rust failure. By observing manufacturers recommendations on prop sizing to engine RPM you can minimize soot thus potentially reduce longer periods of moisture in the elbow..

I know one guy with a Yanmar who had over 12 years on his exahust elbow when he sold the boat and another who needed a new one every four and they both had the identical engines. One guy was propped almost spot on and the other over propped by about 450 RPM.

An exhaust elbow is not a spare I would carry unless going to very remote places with an engine known to chew through exhaust elbows..

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Old 27-12-2010, 06:59   #5
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My experience was the boats that ran more, needed fewer elbow replacements.
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Old 27-12-2010, 07:12   #6
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My Boats 4 years old I have twin Yanmars with Stainless Steel elbows - 1 failed last year from a small crack in the middle of the weld -
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Old 27-12-2010, 15:15   #7
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Stainless Steel Exhaust Mixer fails in 150 hours

Hello,
I have a Next-Gen 3.5 Kw generator. The exhaust mixing elbow failed after 150 hours and about a little more than a year. We purchased a replacement elbow from Next-Gen and it has also failed after 250 hours. The units develops hairline cracks in the actual metal, NOT the weld and then leak. The manufacturer says this is normal and if we ran the generator for many more hours continuously, we wouldn't have this problem. They say the stainless steel fails because we only run the generator for an hour or two at a time. Seems to me that stainless steel is not the right product for a cruising sail boat.

At $400, I am not keen to replace the exhaust mixer with another stainless steel one. Do I have any other options? Can I repair it? I read that some exhaust mixers are made of cast iron. Does anyone make exhaust mixers that might fix my generator or would I have to have one custom made if I wanted it made in a different material?

On the first mixer, we tried using JB Weld to cover the cracks. It worked for a short time then failed. JB Weld said that we either didn't put a thick enough coating on or didn't rough up the steel enough. They said it should have worked.

We are in Grenada and need to do something. Any advice would be appreciated. We have JB Weld and Fas-Weld Aluminum Repair Epoxy Putty on board. I'm not sure what the local stores will have available.

Thanks for your input.
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Old 27-12-2010, 15:39   #8
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iM TAKING MINE IN AND HAVING IT WELDED I
think this should work fine
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Hello,
I have a Next-Gen 3.5 Kw generator. The exhaust mixing elbow failed after 150 hours and about a little more than a year. We purchased a replacement elbow from Next-Gen and it has also failed after 250 hours. The units develops hairline cracks in the actual metal, NOT the weld and then leak. The manufacturer says this is normal and if we ran the generator for many more hours continuously, we wouldn't have this problem. They say the stainless steel fails because we only run the generator for an hour or two at a time. Seems to me that stainless steel is not the right product for a cruising sail boat.

At $400, I am not keen to replace the exhaust mixer with another stainless steel one. Do I have any other options? Can I repair it? I read that some exhaust mixers are made of cast iron. Does anyone make exhaust mixers that might fix my generator or would I have to have one custom made if I wanted it made in a different material?

On the first mixer, we tried using JB Weld to cover the cracks. It worked for a short time then failed. JB Weld said that we either didn't put a thick enough coating on or didn't rough up the steel enough. They said it should have worked.

We are in Grenada and need to do something. Any advice would be appreciated. We have JB Weld and Fas-Weld Aluminum Repair Epoxy Putty on board. I'm not sure what the local stores will have available.

Thanks for your input.
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Old 06-01-2011, 01:46   #9
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I have a 3YM30 Yanmar in a 2004 Hunter 33 and am on my third elbow. Frst one clogged round 200 hours and the second one around 500 hours. The Yanmar service guy insisted they be replaced and would not countenance clening them out.
I think it is a very weak point on these engines almost to the point of not fit for purpose. (They are cast iron). When I questioned Yanmar indicating that this number of hours would be impossible to tolerate on a commercial vessel the only answer I got was that they don't last long on sail boats bcause we don't work themhard or long enough! Considering that they are probably the most common sailboat engine this is clearly crazy.
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Old 06-01-2011, 02:22   #10
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friend of mine-- former one, cleaned his last year and is doing nicely with it that way-- we put 5000 miles on after cleaning. dont know how many hours, as we sailed mostly.
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Old 06-01-2011, 03:30   #11
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Ahoy, mine failed at 900 hours on a 23hp nanni diesel, not the exhast but the small pipe where the salt water inlet is, it just corroded off, had a new anode in the mixer as well!
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Old 06-01-2011, 18:14   #12
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I have a 3YM30 Yanmar in a 2004 Hunter 33 and am on my third elbow. Frst one clogged round 200 hours and the second one around 500 hours. The Yanmar service guy insisted they be replaced and would not countenance clening them out.
I think it is a very weak point on these engines almost to the point of not fit for purpose. (They are cast iron). When I questioned Yanmar indicating that this number of hours would be impossible to tolerate on a commercial vessel the only answer I got was that they don't last long on sail boats bcause we don't work themhard or long enough! Considering that they are probably the most common sailboat engine this is clearly crazy.
Sounds like you may be over propped...
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Old 07-01-2011, 07:19   #13
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We installed a Yanmar 2GM20F in our old boat in '87. At the time the Yanmar dealer in Long Beach, Ca. indicated we should expect to replace the mixing elbows at roughly 500 hour intervals so we bought several spares (then quite cheaply). In fact, 500 hours was about where they had to be replaced. Fortunately, it was a relatively easy but somewhat messy job.

FWIW...
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Old 08-01-2011, 07:27   #14
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I have a Perkins 4-108(1985 vintage) and over the past 25 years have just replaced the elbow once. That was about three years ago when I took the old elbow to a Amish weld shop and had them make a new stainless steel one for around 300 bucks. The old elbow had been repaired for small leaks during the previous 20 year period using JBWeld and then it was removed and spot welded which lasted for maybe another 6 years before replacing the whole thing. With the exception of going down the ICW to Florida and then up to Block Island the engine gets used about 50 hours per year during the sailing season here on the Cheaspeake (March through November). During the winter months the raw water side is filled with anti freeze which I think helps in holding down the corrosion. I run the engine about 80% of the WOT setting(2300rpm) which is much lower than the specs for the engine(3600rpm). I know that I'm over proped but that does not seem to cause premature failure of the exhaust elbow.
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Old 08-01-2011, 08:40   #15
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I have a pair of stainless steel risers that have been there for 15 years. When the engines were changed out 2.5 years ago, there was no pitting. I find it interesting that my risers lasted longer than the first set of B-Series engines. These risers have at least 15,000 hours on them. If they only lasted 500 hours then I would have had to change them out 30 times by now.

If there is someone who makes stainless steel risers for your engine, it is probably worth the extra expense to go stainless...just for the hassle factor and the reliability factor alone.
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