Re: [Amel Yacht Owners] Yanmar Engine issue

Mark Erdos



It sounds as though you are sucking in air somewhere. It you have a loose fitting or seal prior to the raw water pump, air is less resistant than water to move by the raw water pump. The raw water pump is self priming meaning, if you do have air in the system, it should pass it though and pull water from the strainer. But, the system has to be sealed or it will move air. To remedy this, start at the transmission and work your way to the raw water pump. You are looking for broken or lose hose clamps (everything should be double clamped on this side of the pump). Also, check the hoses along this area. A small pin hole will cause the systems you describe. Especially check the hoses near the clamps as this is where they tend to fail. Once you get to the pump, check the o ring seal on the cover. At some point in the path you should have an “ah ha” moment. This should solve your problem.


One more thought: I’m not sure if this could cause the symptoms described but check the cap on the strainer to ensure it is on tight.




With best regards,




Super Maramu 2000

Hull #275

Currently cruising:  Green Turtle Cove – Abaco Islands - Bahamas


From: amelyachtowners@... [mailto:amelyachtowners@...]
Sent: Saturday, January 02, 2016 12:41 PM
To: amelyachtowners@...
Subject: [Amel Yacht Owners] Yanmar Engine issue



Surely there is an easy fix but…this has me stumped:

I have the Yanmar 4JH-3-HTE engine on my SM2000 (#404).  When I start it up cold, no water flows from the impeller to the heat exchanger.  A large air bubble forms in the bottom of the translucent hose that goes from the impeller and, of course, the engine begins to overheat if not shut down.  (Before I detected this problem, we overheated and melted the plastic muffler early into the Salty Dawg venture last month). 

Impeller recently replaced and working fine, water is flowing freely from the sea chest (e.g., when the heads are filled or the air conditioning is turned on), belts are new and snug.  There are no leaks, water or air, that I can detect anywhere along the path from the sea chest to and through the engine. 

But here’s the interesting part:

When I disconnect the hose from the heat exchanger (the hose that goes from the impeller to the heat exchanger), lay it down on the floor of the boat below the level of the impeller, and then start the engine, the water (and bubbles) starts flowing forcefully through the hose into the bilge—after which, with engine still running, I immediately slam the end of the hose back into the heat exchanger and tighten it down, the water continues to flow forcefully as it should (but no bubbles), the engine remains cool, and all is right with the world.

It seems to stay ‘primed’ if I shut it down and start it again after only a few hours.  However, if I start the engine up after a couple of days of not running the engine, I then have the same symptoms and cure it with the same solution.  

Thoughts? Ideas? THANKS!

Rick Grimes

S/V Rascal

Amel SM2K (#404)




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