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)