Yanmar 2QM15: strange overheating incident - SailNet Community
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post #1 of 20 Old 07-10-2013 Thread Starter
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Yanmar 2QM15: strange overheating incident

I've had my (1981) boat for about 6 months, and the engine (which was a concern of mine, due to uncertain history) has run flawlessly until last week.

I took some friends out for the afternoon, motoring out of the marina and for about 30 minutes to find some wind. Shut down the engine and sailed for about an hour. Kids started getting cranky, so I pulled down the sails and started up the motor.

After idling in neutral for about 1 minute, I get a high temperature alarm, so I shut the engine down. Guage reads about 160F (it's raw water cooled, so normal temp is about 120F). Waited about 10 minutes, but temp guage doesn't drop, so I tentatively restart to get some cooling flow. Although water appears to be coming out the exhaust, the temp stays high and alarm still sounding.

So I shut it down again and start checking stuff. Oil level is good, raw water strainer is clean (but we're drifting through a heavy moss/algea/seaweed current line). I can't find any obvious problems, so I start it one more time, and this time, the temperature rapidly drops, and everything returns to normal. Motored back home without incident.

I've had it out once since then, with no issues.

Any idea what might have happened? My guess is that a got a piece of debris on the hull strainer, which eventually dropped off on its own. Planning to change out the impeller soon, just in case that was somehow related.

(Incidentally, is there some law of nature that says stuff only goes wrong when you've got guests on board?)
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Re: Yanmar 2QM15: strange overheating incident

Could easily have been a plastic bag that got sucked over your raw water input and later it drifted away.
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post #3 of 20 Old 07-10-2013
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Re: Yanmar 2QM15: strange overheating incident

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(Incidentally, is there some law of nature that says stuff only goes wrong when you've got guests on board?)
Just wait till you have a date on board!

Congrats on the boat. Yanmar's are great motors.


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post #4 of 20 Old 07-11-2013
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Yanmar 2QM15: strange overheating incident

If you had good water flow when the temp was high, I would say you might have a sensor problem. I'd take a look a the thermostat connections, and maybe pull the thermostat and see if its all gunked up and not opening.
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post #5 of 20 Old 07-11-2013
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Re: Yanmar 2QM15: strange overheating incident

Yes, could be thermostat or problem with the alarm circuit. Hard to believe it would overheat in only 1 minute of idling.
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Re: Yanmar 2QM15: strange overheating incident

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Yes, could be thermostat or problem with the alarm circuit. Hard to believe it would overheat in only 1 minute of idling.
I thought about that too. Difficult to tell for sure, so I'm going to take a wait and see approach.
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Re: Yanmar 2QM15: strange overheating incident

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Yes, could be thermostat or problem with the alarm circuit. Hard to believe it would overheat in only 1 minute of idling.
I thought about that too. Difficult to tell for sure, so I'm going to take a wait and see approach. When I do my annual engine maintenance this year, I'll probably change out the T-stat just in case.
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Re: Yanmar 2QM15: strange overheating incident

I had the same problem last fall with my 2QM20 last fall in Hobe sound Fl. I had water flow and a clean raw water strainer. After looking things over 3 times and pulling a few hands full of hair out I finally pulled the hose from the seacock to find some sea grass trapped. it wasn't enough to stop water flow but still made engine over-heat.

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post #9 of 20 Old 07-11-2013
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Re: Yanmar 2QM15: strange overheating incident

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Originally Posted by Rusty123 View Post
I've had my (1981) boat for about 6 months, and the engine (which was a concern of mine, due to uncertain history) has run flawlessly until last week.

I took some friends out for the afternoon, motoring out of the marina and for about 30 minutes to find some wind. Shut down the engine and sailed for about an hour. Kids started getting cranky, so I pulled down the sails and started up the motor.

After idling in neutral for about 1 minute, I get a high temperature alarm, so I shut the engine down. Guage reads about 160F (it's raw water cooled, so normal temp is about 120F). Waited about 10 minutes, but temp guage doesn't drop, so I tentatively restart to get some cooling flow. Although water appears to be coming out the exhaust, the temp stays high and alarm still sounding.

So I shut it down again and start checking stuff. Oil level is good, raw water strainer is clean (but we're drifting through a heavy moss/algea/seaweed current line). I can't find any obvious problems, so I start it one more time, and this time, the temperature rapidly drops, and everything returns to normal. Motored back home without incident.

I've had it out once since then, with no issues.

Any idea what might have happened? My guess is that a got a piece of debris on the hull strainer, which eventually dropped off on its own. Planning to change out the impeller soon, just in case that was somehow related.

(Incidentally, is there some law of nature that says stuff only goes wrong when you've got guests on board?)
Have you ever checked or replaced the engine zincs? When they deteriorate they can send "chunks" into the raw water cooling system.
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post #10 of 20 Old 07-13-2013 Thread Starter
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Re: Yanmar 2QM15: strange overheating incident

Went out today, ran the engine hard for about three hours. Temp was stable, but about 10F higher than normal. I'm suspicious of the thermostat.

1981 Spirit 28 "Bonnie Lass"
Bremerton, Washington
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