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Old 20-10-2019, 16:23   #1
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Yanmar 4LH Exhaust Telltail or Blocked?

We have a Nauticat 42 which we bought a couple of years ago. A couple of weeks ago while leaving a marina someone on a passing sailing boat told me that our exhaust needed to be cleaned.

The indicator for him was the stream of water exiting a nozzel above the main exhaust which streams water out like a jetski telltale.

My assumption was that this was just that a telltale. He seemed to think that it was as a result of a blocked exhaust and was unique to Nauticat's. Water does still come out of the exhaust but I'm wondering if there's any merit to his comments.

Photo below of the box he suggested (not ours, lost that photo..) cleaning out with caustic soda.



I've no idea what that specific part of the exhaust is and/or the best way to clean it, other than the suggestion of caustic soda.

Has anyone had similar experience/issues. I haven't had the time to pull the piece off but it does give me some concern.

Many Thanks!
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Old 21-10-2019, 21:09   #2
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Re: Yanmar 4LH Exhaust Telltail or Blocked?

Hi Duncan-m
The circled part in the photo is the aqualock and is unlikely to be the cause of the water jet from what I assume is the siphon break hose from the vent loop. Usually the water flow from an overboard siphon break is a steady flow at full power and a slight trickle at idle, rarely a jet of water. The observant "passing yachtguy" might be right about a raw water system restriction causing the jet but its more likely to be in the mixer elbow seen under your red arrowhead. Incidentally the raw water circuit seems to be higher on the 4LH series, possibly due to the longer trip through the engine coolers rather than just the short route from the pump, into the heat exchanger and then the exhaust via the mixer elbow. One of the boats here has twin 4LH's and it's blown out a raw water hose on 3 occasions (which is unusual) so maybe the high vent loop pressure is normal and not a symptom of high back pressure.
In your photo it's difficult to see where the vent loop piping might be.
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Old 22-10-2019, 05:07   #3
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Re: Yanmar 4LH Exhaust Telltail or Blocked?

The smaller upper hose is likely a "breather hose" (1).
The height of the cooling water injection point into the exhaust system, relative to the external waterline, is of great importance. If the water injection point is 15 cm or more above the waterline, the cooling water may be injected directly into the exhaust system. However, if the water injection point is less than 15 cm above the waterline (or even below it) there is a risk that the cooling system will siphon water through the intake, once the engine is stopped. This water will fill up the exhaust system and eventually get back into the engine cylinders via the exhaust valves. This siphon action may be prevented by having a breather hose (1) in the cooling water line, or by fitting an air vent (2).


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Old 22-10-2019, 05:51   #4
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Re: Yanmar 4LH Exhaust Telltail or Blocked?

I meant to say that the raw water pressure seems to be higher in the 4LH series than other yanmars.
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Old 22-10-2019, 12:46   #5
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Re: Yanmar 4LH Exhaust Telltail or Blocked?

Quote:
Originally Posted by skipperpete View Post
Hi Duncan-m
Usually the water flow from an overboard siphon break is a steady flow at full power and a slight trickle at idle, rarely a jet of water.
Yeah we're heading towards jetski pressure at 2000rpm so based on what you're saying passing yachtguy might be onto something...

Thanks both for the input and detailed explanation, it's much appreciated. I'll investigate and let you know what I find out.
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Old 22-10-2019, 17:49   #6
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Re: Yanmar 4LH Exhaust Telltail or Blocked?

My Yanmar 3GM had a small diameter hose that dumped into the muffler. Don’t know if it’s for anti syphon or what but it put out a steady stream of water when the mixing elbow clogged up and didn’t allow cooling water into the exhaust the usual way. Might want to check your mixing elbow to be sure it’s working. If that fitting does the same thing as the one on our engine it could be an indication of mixing elbow problem.
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Old Yesterday, 05:18   #7
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Smile Re: Yanmar 4LH Exhaust Telltail or Blocked?

Just wanted to drop a note to say thanks to everyone who replied. You were all correct!

The mixing elbow had deteriorated and had become quite blocked. Having removed it and had a local marine engineer in Rotterdam (Dirk) attempt to clear it up we decided to opt for a new one.



They're pricey, 500 inc gaskets etc but having fitted the new one the results are clear. The overflow now only pushes water through when the engine is running around 2000rpm. The rest of the time there's not a trickle.

In addition, there is now a much better flow of water out of the exhaust.

From the photos above it's likely, this would have failed sooner or later so glad that we caught it before it was too late.
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Old Yesterday, 05:34   #8
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Re: Yanmar 4LH Exhaust Telltail or Blocked?

Great to hear that you got er fixed
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Old Yesterday, 17:04   #9
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Re: Yanmar 4LH Exhaust Telltail or Blocked?

I'm too late for your fix but next time try exhaust elbow.com who makes 316L s.s. elbows much cheaper. also aftermarket marine may have them
I make my own & have no association with exhaust elbow just trying to help a fellow yanmar owner avoid getting reamed by the Yanmar mafia.
316ss elbows last waay longer too
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