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Old 25-04-2022, 04:58   #1
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Yanmar 4JH3-TE Leaking Seawater

Out 2002 Island Packet 423 with 6300 engine hours started leaking pure seawater into the pan under the engine, about 5 gal over 24 hr operating at 2400 RPM without overheating. We cannot see the leak either while idling or under load but suspect it comes from the exhaust system. Any ideas re how to confirm and locate the site of leakage? Is it safe to operate until we navigate to a mechanic?
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Old 26-04-2022, 13:39   #2
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Re: Yanmar 4JH3-TE Leaking Seawater

A couple of thoughts. We have an older version of this engine. There are small/tiny seacocks for draining water for winterizing, that can be left open, or they can get stuck partly open. Common problem. There are usually some 1/4" or so hoses on them, directing them down to the bilge.



Also, the water pump">raw water pump probably has a weep hole in it, to tell you when it's going south. Might need a new pump.



Could also be the heat exchanger seals.
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Old 26-04-2022, 14:37   #3
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Re: Yanmar 4JH3-TE Leaking Seawater

Bill:
Thank you much for the reply. All good thoughts. I'll pass them on to my captain. We left the boat in a marina in Hilton Head.
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Old 26-04-2022, 15:16   #4
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Re: Yanmar 4JH3-TE Leaking Seawater

I have had 3 sw leaks from my Yanmar

1 was a small crack in the heat exchanger outlet flange

2 were fron the hose connection right under that

I found the crack between finding the other two. In hindsight i think that flange had been leaking 10 years and caused he other 2. The clamp corroded and it got loose. Looked fine unless you pushed on it.
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Old 26-04-2022, 15:27   #5
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Re: Yanmar 4JH3-TE Leaking Seawater

[QUOTE=John Bowers;3612637]Out 2002 Island Packet 423 with 6300 engine hours started leaking pure seawater into the pan under the engine, about 5 gal over 24 hr operating at 2400 RPM without overheating. We cannot see the leak either while idling or under load but suspect it comes from the exhaust system. Any ideas re how to confirm and locate the site of leakage? Is it safe to operate until we navigate to a mechanic?[/

To locate the leak carefully follow the circuit: hose from strainer to raw water pump, raw water pump, hose from water pump to heat exchanger, hose from heat exchanger to anti siphon to mixing elbow, exhaust hose to muffler. The leak is somewhere along that path and may be a broken clamp, cracked hose, cracked muffler, etc.

Leaks never get better, they always get worse.
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Old 28-04-2022, 03:34   #6
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Re: Yanmar 4JH3-TE Leaking Seawater

Tracing the route of seawater is what we did to no avail. I suspect we will need to repeat. Is there any way of pressure testing the system the way you do in an automobile radiator?
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Old 28-04-2022, 05:47   #7
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Re: Yanmar 4JH3-TE Leaking Seawater

To pressure test it would be necessary to seal the exhaust through hull on the transom and plumb some sort of inflation valve into the raw water piping. Close the sea cock and pressurize the system.

First though, use a paper towel to test each hose connection and fitting. This often identifies the source of a leak that can’t be seen.

One last thought, is there a positive shaft seal vent hose routed through the engine room that is cracked or has fallen to near sea level?
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Old 28-04-2022, 08:25   #8
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Re: Yanmar 4JH3-TE Leaking Seawater

You could attach a hose to the supply line and plug the hose into the exhaust line. May have to remove the sw impeller. I would be worried that the pressure would be too high as I bet city water is a lot higher than what normally goes through the system.

There are fluorescent dyes for doing leak testing I bet would work better. Set up a pump loop to/from a bucket with an aux pump. I would say this is the way to go.
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Old 28-04-2022, 12:40   #9
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Re: Yanmar 4JH3-TE Leaking Seawater

Do not pressure test the raw water as recommended above. Water will back up from the exhaust elbow into your exhaust manifold and cylinders and cause major problems.

If you were to plug the raw water flow just before it reaches the exhaust elbow you could make it work.
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Old 11-05-2022, 07:04   #10
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Re: Yanmar 4JH3-TE Leaking Seawater

Quote:
Originally Posted by John Bowers View Post
Out 2002 Island Packet 423 with 6300 engine hours started leaking pure seawater into the pan under the engine, about 5 gal over 24 hr operating at 2400 RPM without overheating. We cannot see the leak either while idling or under load but suspect it comes from the exhaust system. Any ideas re how to confirm and locate the site of leakage? Is it safe to operate until we navigate to a mechanic?
So

have you found anything and if so what was it and and how did you find it?
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Old 16-05-2022, 07:48   #11
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Re: Yanmar 4JH3-TE Leaking Seawater

A mechanic found a crack in the fiberglass elbow of the exhaust system. It has been repaired, but I haven't heard the result of testing the system under load after the repair cured.
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