Hi, Ron.

I thought I would relate to you my travails with the cooling system of my venerable Yanmar 1GM10. It is a cautionary tale for those seeking to address the obstructive uropathy inherent in these boats. As a review, the raw water comes in through a seacock and passes a strainer to a water pump. Said water pump has an impeller that is a vulnerable spot in these engines. The pump is driven directly, not via a belt as in some engines. The water then passes to a “T” fitting that divides the stream between the block and the thermostat.

Moving downstream, the thermostat controls the flow from the bock. This is different from car engines where the thermostat controls flow from the radiator. Here, when the engine is cold, the thermostat blocks flow in the block by jamming up the exit. When the engine warms up, the thermostat opens and allows water to exit from the block, thus cooling the engine. From the thermostat, the water goes through an anti-siphon “U” fitting and then exits through the mixing elbow that allows the water to combine with exhaust gases, thus cooling them.

The thermostat area is the prostate of the engine. Considering that boats are traditionally female and females traditionally do not have prostates, the analogy is a bit flawed, but hell, it’s the 20’s.

Back to the boat. Prior to launch, I replaced the impeller in the water pump despite the old one looking just fine. I also replaced the anode and the secondary fuel filter, and changed the oil and filter (irrelevant to this discussion, but I want to demonstrate my compulsiveness). I ran a hose into the strainer and fired her up on the hard and she ran beautifully. Launch day came, and Maya Elena kissed the waves. As before, her engine coughed once and fired right up. Then, disaster struck in the form of an overheating alarm after about 4 minutes, just enough time for the block to heat up.I limped to a slip and thought that I could fool the Yanmar gods by waiting and then starting again. 4 minutes went by and the piercing alarm went off again. Using my best internal medicine training, I reasoned that the flaw had to be in the thermostat. My yard did not have a new one in stock so I called around and sure enough, found one in Yarmouth, a mere 2 hour drive away.

The next day was Saturday but the Yarmouth yard kindly accepted a credit card and put the thermostat outside for me. In the meantime, I removed the old one and went home to test it. It worked fine. But it couldn’t have as my rapier-like reasoning told me that it was flawed. So early the next morning, I drove to Yarmouth, picked up my new thermostat and drove home. Sunday dawned, bright and clear with a perfect breeze to sail home. I installed the new thermostat, turned over the motor, and 4 minutes later was rewarded by a piercing alarm.My next hypothesis was a clogged mixing elbow, well known to be a spot of vulnerability for these motors.

I pause here to remark on the physical location of this motor on a Dolphin. Mine in particular, nee Tern, then Resilience, now Maya Elena (after performing all the appropriate exorcisms to placate those spirits that I have detailed in a past note) has an aftermarket motor. She originally was fitted with an outboard in the lazarette. Sometime around 1992, as best as I can determine, she was substantially altered with the Yanmar 1GM10 shoehorned under the cockpit sole and easily accessible behind the stairs, easily, that is, for the average 5 year old. I am 6’1 and 175 lbs, and more importantly am 71 years old. There is nothing on that motor that is easily accessible to me.

The mixing elbow resides deep within the bowels of the engine compartment but with the deft application of obscenity in four languages, I removed it. To say that it was pristine is an understatement but I went through the motions and cleaned it anyway. After reinstallation, the engine fired right up and ran like a top…for four minutes until the piercing wail of the alarm jolted me back from the land of self-congratulations. At this point, I reasoned that the entire water pump had to be defective. Fortunately, the parts guy with whom I had now developed a close relationship, not only had one in stock but also had a gasket, as each one of these devices needs a gasket replaced when it is removed.Not having the time to buy a lottery ticket as I was sure to be a winner, I rushed down, folded my frame into the requisite hairpin shape, and replaced the water pump.

Of course, that also required draining all the oil and refilling, despite my having done that on the hard. Nonetheless, feeling victorious, I fired her up and this time, she ran for 3.9 minutes before the alarm went off. As a scientist, I like to consider myself data-driven so I took a deep breath and reasoned that it just had to be the thermostat. Fortunately, my parts guy now had one in stock so I put in yet another. You guessed it – not the problem. I now sought consultation from my neighbor Peter who, in addition to being a brilliant anthropologist, is also a fine cocktail mixer, and after the first gin and tonic I was able to finally stand up to my complete height. I reasoned in an alcohol induced-haze, that the entire block had to be caked in salt so the next day I put “Salt Away” (a fine product) in the strainer and ran it into the engine. I let it sit for 24 hours and…you guessed it, four minutes.

The next day at 7:30, the mechanic was able to look at the motor. At 7:40 he called to tell me that it was now running great. What he did was take off the hose to the “T” fitting (remember the T fitting) and remove a piece of salt that was blocking entry into the block. The motor runs perfectly and they are a happy boat. Based on this, I now know more about the Yanmar 1GM10 cooling system than any other internist on Spruce Head Island and look forward to a fine summer of sailing, once I can stand straight again

Cliff

Postscript: I was given this 1GM10 Parts Catalogue by the parts guy at Journey's End Marina (Rockland, Maine). It is absolutely indispensable for people with 1GM10’s

https://www.mecanique-plaisance-finistere.com/yanmar/pdfmoteur/1gm10.pdf

Reference added in the Technical Index

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