Al, This sounds like a similar problem I experienced with my old C&C 29 which had a raw water cooled 2QM15. The alarm only came on only after the engine was shutdown for a short period of time and then restarted. I would even let the engine cool at idle speed for a good few minutes before shutting down. I tried many things, and listened to may good suggestions (air lock, pump wear, …), but in the end the problem turned out to be a bad thermostat sender.
Maybe that’s your issue too. Do you have a separate sender for the alarm and for the gauge? If so, then it is unlikely that both would be bad. But if not, I would start there. Paul - Paul E. 1981 C&C 38 Landfall S/V Johanna Rose Carrabelle, FL http://svjohannarose.blogspot.com/ > On Oct 19, 2015, at 9:03 AM, cnc-list-requ...@cnc-list.com wrote: > > Date: Sun, 18 Oct 2015 16:08:19 -0700 > From: Al Serrato <aserrat...@yahoo.com <mailto:aserrat...@yahoo.com>> > To: "cnc-list@cnc-list.com <mailto:cnc-list@cnc-list.com>" > <cnc-list@cnc-list.com <mailto:cnc-list@cnc-list.com>> > Subject: Stus-List Engine Overheat Question > Message-ID: <411a5ff3-f777-4f52-9bf4-0d90cac65...@yahoo.com > <mailto:411a5ff3-f777-4f52-9bf4-0d90cac65...@yahoo.com>> > Content-Type: text/plain; charset=us-ascii > > I'm looking for advice on a situation that arose yesterday. I have a 34 with > a 3GMD diesel with raw water cooling. I motored for about 45 minutes at 2000 > rpm and then shut the engine down. Everything was running smoothly. The temp > gauge showed the normal 100 degrees and I could hear water from the exhaust. > I sailed for about half hour but then lost the wind and turned the motor on. > The high temp alarm stayed on and the gauge showed 140 degrees. I shut it > down and checked the water filter, which looked fine. I tried starting it a > couple more times with the same result, so I sailed back to my harbor. When I > went to start it, everything worked fine again, and I ran the motor for a > good 30 minutes with no issues. The gauge stayed at 100 the whole time and no > alarm. > > I initially thought it might have been the impeller (which is about 1.5 years > old right now), but when the problem arose I didn't check for the sound of > exhaust water. Since it was working back at the harbor, I don't think the > impeller was bad. I'm starting to think that the sending unit malfunctioned > and then reset itself somehow but that's never happened before. > > I'm not sure what temp triggers the high temp alarm and whether the same > sending unit goes to both the alarm and the gauge. > > Am I missing something obvious? > Were there other steps I should have taken to diagnose it? I was of course > concerned to run the engine for long if it was overheating. > What next steps should I take, since everything seems fine right now. > > Thanks in advance for any help. > > Al Serrato > C & C 34 > Fidelity > San Francisco Bay
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