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Old 23-05-2011, 05:04   #1
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Mixing Elbow Scheduled Replacement ?

My boat has an 11-year old Yanmar 4JH3HTE engine with about 1150 hours on it (320 of which I have put on myself in the last two years).

I recently found a Yanmar manual which specifically deals with routine maintenance. Previously I had been working with the regular service manual which is mostly concerned with overhaul procedures.

I was surprised to see there that replacement of the mixing elbow is a regularly scheduled maintenance item, to be done every 1,000 hours or 4 years.

Do any of you replace your mixing elbows on a scheduled basis? Or do you wait for them to start leaking? Should I be worried?

P.S.

Two different Yanmar engineers I have spoken with pooh-poohed the idea of regular valve adjustments. When I first bought my boat two years ago, I had a very extensive service done on the engine including replacing all belts and hoses. The engineer actually refused to adjust the valves -- he said it would be a waste of money. The Yanmar manual says to do this every 2 years or 500 hours.

I don't really see why a marine engine would be any different from an automobile engine with regard to valve adjustments. I've adjusted a lot of valves over the years -- maybe I should just roll up my sleeves and do it? How often do you guys adjust your valves?
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Old 23-05-2011, 05:21   #2
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Re: Mixing Elbow Scheduled Replacement?

I noticed the P.O. of my crealock changed the mixing elbows regularly. On my old boat, I just had one go bad so there was no cooling water moving through the system. It took a while for me to diagnose, after changing impellers, etc, but water flowing now. If you are not setting out on a long cruise, you can watch water flow and change at the appropriate time. Otherwise, I'd consider knocking it out as mine went bad on a 2GM20 at 640 hours.

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Old 23-05-2011, 05:37   #3
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Re: Mixing Elbow Scheduled Replacement?

We changed the mixing elbow on the 3gm Yanmar before we put our last boat up for sale. Not sure it had ever been done before. My diesel maintenance course instructor suggested that it was possible to take the elbow off and inspect it. Not sure I would ever do that without just replacing it as it took most of a full day to get it out as it was virtually impossible to reach. The inside was almost fully plugged with deposits and it never leaked so can't just assume that if it's not leaking it's good. The engine was over 20 years old and kept in the Chesapeake Bay. Never adjusted the valves as the engine ran fine so can't comment there. My advice would be that if it concerns you then change it out. We changed ours because another boat on our dock had the same engine, newer and when he changed it out he showed it to us.
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Old 23-05-2011, 05:50   #4
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Re: Mixing Elbow Scheduled Replacement?

My 4JH3E is seven years old, 1700 hours still the original mixing elbow.
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Old 23-05-2011, 06:36   #5
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Re: Mixing Elbow Scheduled Replacement?

Whilst it is eventually going to leak as it corrodes away, it could be worth checking that it hasn't blocked up with carbon as its a key location.

Probably 4 bolts and a gasket providing they don't snap on the way out.

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Old 23-05-2011, 06:50   #6
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Re: Mixing Elbow Scheduled Replacement?

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Originally Posted by Pete7 View Post
Whilst it is eventually going to leak as it corrodes away, it could be worth checking that it hasn't blocked up with carbon as its a key location.

Probably 4 bolts and a gasket providing they don't snap on the way out.

Pete
Have you changed yours? Mine is reasonably accessible so I'm thinking about buying a new one and just changing it out. If the old one is still serviceable, keep as spare.

But I have other things to do on the boat (to say the least!), if this is gilding the lily, maintenance-wise.

No one has commented on valve adjustments. Why are sailors apparently so much more complacent about valve adjustments than are motorists?

I had a number of Porsche 911's over the years (still have a 1970 911S) and what a b*tch the valve adjustments are on those. You need to be an asbestos octopus to do it easily. Four valve covers, two of them under the car. Crawl back out from under the car after every adjustment to turn the crankshaft to the next position. It's so awkward, you can't get a regular feeler gauge under the rocker arms -- you have to buy one with a special handle. Nevertheless, I and every other Porschist I ever knew always adjusted them religiously -- I think every other oil change if I remember right. Why do we let our marine diesels go for years without valve adjustments?! Is there something I don't know??
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Old 23-05-2011, 06:54   #7
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Re: Mixing Elbow Scheduled Replacement?

Adjust the valves...inspect and/or replace the mixing elbow. You will rest easier knowing these items have been taken care of.
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Old 23-05-2011, 07:01   #8
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Re: Mixing Elbow Scheduled Replacement?

Hmm....come to think of it, I have never known anyone adjust the valves on a tractor (older simple diesel tractors); maybe they do but I can't recall anyone doing it. FWIW.
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Old 23-05-2011, 07:11   #9
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Re: Mixing Elbow Scheduled Replacement?

Buy a new one, keep the old one, boil out the old one with acid and change them out every two years.
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Old 23-05-2011, 07:13   #10
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Re: Mixing Elbow Scheduled Replacement?

DH, the previous owner replaced ours about 5 years ago at about 1900 hrs. We have added about 200 hours, so will check in a couple of years. We have replaced the first piece of exhaust hose from the elbow to the water trap as it went a bit soft on a sharp bend. If that suddenly goes it can really make a mess of your day.

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Old 23-05-2011, 07:17   #11
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Re: Mixing Elbow Scheduled Replacement?

If it is the same elbow that's on my 3m30F then it is something that I worry about, as once it corrodes through it will dump water into the engine. I pulled the hose off of mine after around 5 years and stuck a mirror up there to look around. No carbon build up and just surface rust. I run my engine mostly at 80% throttle and have to go through a set of locks to get to my dock on a lake, so it's well flushed with fresh water when I'm done.

I am considering replacing the elbow with one where the injection point of water can't ever get to the engine in failure. Downside is that the exhaust pipe has to be lagged for a few inches until you get to the injection point.

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Old 23-05-2011, 07:29   #12
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Re: Mixing Elbow Scheduled Replacement?

Quote:
Originally Posted by Dockhead View Post
I was surprised to see there that replacement of the mixing elbow is a regularly scheduled maintenance item, to be done every 1,000 hours or 4 years.

Do any of you replace your mixing elbows on a scheduled basis? Or do you wait for them to start leaking? Should I be worried?
Here is my take: you can replace it on your schedule, or on its schedule, which under Murphy's Law will be at the most inopportune time. It might cause issues beyond leaking, as a restricted elbow can play havoc with the cooling system. As others said, just replace it and keep the old one as spare.
Quote:
I had a number of Porsche 911's over the years (still have a 1970 911S)
Valves: I have yet to find a Yanmar where the valves are out of adjustment before I comply with the customer's insistence that I adjust them. Comparing a low rev, high torque (Yanmar) diesel to a high rev, air cooled gas engine (Porsche) isn't a useful strategy for maintenance. Your boat diesel comes up to a throttle setting and stays there for hours at the same rpms; the Porsche is constantly changing rpms and throttle settings.

Diesel: "chug chug chug..." Porsche: "Vrooom, VARoom, zoom, vroom..."
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Old 23-05-2011, 08:23   #13
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Re: Mixing Elbow Scheduled Replacement?

In Fall of last year Dani and I went and visited a friend to go sailing around NC and while in the Alligator river the mixing elbow on his Yanmar failed. Suddenly steam came out of the engine room in a giant puff. We crowded in to see and looked until we saw a hole had opened in the mixing elbow. He pulled the exhaust apart with pipe wrenches while Dani and I were forced to hoist sail and start tacking in the middle of a LOT of traffic. The captain was below working on the exhaust system.

After getting the thing out we then had to hacksaw through one of the exhaust pipes and put it back together. (using a hacksaw on this thick pipe while underway is no fun) The actual hole in the pipe that had opened we repaired with JB Weld and it worked well. When I last spoke to our friend the JB Weld had held for about a year with no leaks.

Personally I wouldn't go through the ordeal again. I'd just replace the thing, or at the very least pull it off and look for problems at say... half the recommended change interval. Keep some high temp epoxy onboard!

Account of our mixing elbow failure here:
NC aboard SV Roannon: Belhaven to Alligator River | SV Sundowner sails again
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Old 23-05-2011, 09:59   #14
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Re: Mixing Elbow Scheduled Replacement?

Hi

I too have a 4JH3-TE 2002 with 1500 hrs on. Mine gave me problems within the first two years where it developped a leak thru a pinhole along the weld. I had it welded and was told it is made of some exotic stainless. I just can't remember the number. Anyway it is awfully thin and flimsy. Other than to sell more parts I wander why Yanmar doesn't design theses thicker and sturdier.

Now I'm due for a replacement since I noticed at the end of last season, it is starting to leak again. Have you proced the parts? I did 7 or so years ago, but can't remember exactly. You may jump when your given the price...

I was wandering if one couldn't have one fabricated out of sturdier and more lasting material. Even if it would end up costing the same, if it would last longer I would be happy.



Michel
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Old 23-05-2011, 10:03   #15
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Re: Mixing Elbow Scheduled Replacement?

Quote:
Originally Posted by Absolute View Post
Buy a new one, keep the old one, boil out the old one with acid and change them out every two years.
Every TWO YEARS?! Does anyone really change them that often?
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