I finally have some info from Yanmar about the problem of Hunter 33 Yanmar 3YM30's overheating above 2800 RPM. My boat is going to be fixed as a result of two Yanmar "Marine Service Advisories" (MSA's). The technical details are: Yanmar MSA # E05-023 for the diagnosis, and MSA E05-025 for the solution and parts spec. Engines with serial numbers lower than (but not including) E05566 are all affected. These MSAs are apparently difficult for your dealer to find. My dealer found out about them at a seminar - he was not notified through the regular channels. The diagnosis is twofold. First the heat exchanger does not effectively cool the engine over 2800 RPM - especially if clogged with bad gunk due to overheating of the coolant. Second the alignment of a hose at the end of the unit can cause a bubble to form. This bubble will move to the coolant pump when the engine gets hot and cause the pump to cavitate. The solution is to a) fix the hose problem and b) install a new design of heat exchanger core which has more tubes. The end caps and O-rings are also replaced and I understand that the end caps have also been redesigned. The delivery time for the new parts is four to six weeks and I expect to have my boat fixed (all under warranty) by the end of January. I will post a note here about the results at that time. The symptoms in the diagnosis exactly explain my boat's problem - overheating after 10 to 20 minutes over 2800 RPM. I am pretty sure this has identified the issue. Whether the new parts solve it . . . time will tell. While this has been a topic of concen to Hunter owners, there is no reason to suppose that it is a problem only on Hunter boats - unless the very tight installation on the 33 is a contributing factor. I note here that when I ran my test routine without the companionway steps installed I did not experience the overheating.
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Best solution
I read many postings on the subject of Yanmar overheating and their many solutions. This posting is, in my opinion, the only one that correctly addresses the problem. The fact remains that your engine will overheat if there is inadequate flow of coolant or raw water to cool the fresh water - period. Air bubbles trapped in the fresh water cooling system will certainly cause overheating since the fresh water cannot flow around the engine block and remove heat. Incidentally, I was able to replicate this problem on my “old” Yanmar after changing my coolant this season. After changing the coolant, the engine will not run over 2800 RPM without over heating. My solution, loosen the plugs on the thermostat housing, squeeze the cooling hose until all air was evacuated from the cooling system. No over heating since.
I read many postings on the subject of Yanmar overheating and their many solutions. This posting is, in my opinion, the only one that correctly addresses the problem. The fact remains that your engine will overheat if there is inadequate flow of coolant or raw water to cool the fresh water - period. Air bubbles trapped in the fresh water cooling system will certainly cause overheating since the fresh water cannot flow around the engine block and remove heat. Incidentally, I was able to replicate this problem on my “old” Yanmar after changing my coolant this season. After changing the coolant, the engine will not run over 2800 RPM without over heating. My solution, loosen the plugs on the thermostat housing, squeeze the cooling hose until all air was evacuated from the cooling system. No over heating since.
Overheating
I had my heat exchanger replaced with a new unit this fall. The story I was told by the Canadain Distributor/Service company for Yanmar was that the engines are shipped without fluids (oil and anti-freeze) to Hunter for their installation and set-up. Apparently the problem was a result of the heat exchnagers being cummed up do to the fact that Hunter filled the heat exchangers with 100%anti-freeze and did not dilute (50/50) as is requird by Yanmar. Lets just hope the overheating problem in the breakin period of the engine does not effect the longevity of the engine and potential problems associated with burning oil.
I had my heat exchanger replaced with a new unit this fall. The story I was told by the Canadain Distributor/Service company for Yanmar was that the engines are shipped without fluids (oil and anti-freeze) to Hunter for their installation and set-up. Apparently the problem was a result of the heat exchnagers being cummed up do to the fact that Hunter filled the heat exchangers with 100%anti-freeze and did not dilute (50/50) as is requird by Yanmar. Lets just hope the overheating problem in the breakin period of the engine does not effect the longevity of the engine and potential problems associated with burning oil.
Response to Robert
Robert, I have heard this story about finger pointing between Hunter and Yanmar and the issue of the wrong coolant. The significance of the Yanmar MSA is that Yanmar now seem to be accepting responsibility for the problem. The replacement exchanger tubes and end caps are redesigned and not simply cleaned and/or replaced. And, it seems to apply to all YM30 engines on Hunter boats or not. I would be interested to know if a) you got the redesigned versions and b) if it has solved the problem. The MSA was dated sometime in October. Was your boat fixed after that? By the way, my dealer tells me that they routinely replace the coolant during commissioning to ensure that it is 50/50 diluted. So with my boat at least, the problem cannot have been Hunter messing up the coolant.
Robert, I have heard this story about finger pointing between Hunter and Yanmar and the issue of the wrong coolant. The significance of the Yanmar MSA is that Yanmar now seem to be accepting responsibility for the problem. The replacement exchanger tubes and end caps are redesigned and not simply cleaned and/or replaced. And, it seems to apply to all YM30 engines on Hunter boats or not. I would be interested to know if a) you got the redesigned versions and b) if it has solved the problem. The MSA was dated sometime in October. Was your boat fixed after that? By the way, my dealer tells me that they routinely replace the coolant during commissioning to ensure that it is 50/50 diluted. So with my boat at least, the problem cannot have been Hunter messing up the coolant.
Getting mine fixed, too
I too suffered from this ongoing overheating problem. Living in Southern Cal, I called Boatswains Locker who is a Yanmar Distributor, and lo and behold my heat exchanger is being replaced as I write. My engine number is 354, so I justed wanted to say "thanks" to all the perseverance having this problem corrected. Happy Holiday and Happy Sailing
I too suffered from this ongoing overheating problem. Living in Southern Cal, I called Boatswains Locker who is a Yanmar Distributor, and lo and behold my heat exchanger is being replaced as I write. My engine number is 354, so I justed wanted to say "thanks" to all the perseverance having this problem corrected. Happy Holiday and Happy Sailing
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