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Old 29-06-2022, 11:43   #1
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Intermittent loss of cooling

My boat is a 1979 30' O'day, with a raw water cooled Yanmar 2QM15 with about 930 hours. We bought her about 18 months ago. Last season, I added a Groco sea strainer and replaced the raw water hoses. We had no issues. At haul out time, the intake strainer of the thru hull was nearly clogged with Zebra mussels. I replaced the strainer with a mushroom thru hull, thinking that if I had to, I could disconnect the hose inside and use a dowel rod to knock the little Zebra buggers loose.

This season, I've had 2 incidents where I was not getting cooling water. Both times we were returning to the dock after some "spirited" sailing. The first time, we were healing about 20 degrees when I started the motor. No water burping out the exhaust, even with a blip of the throttle. I shut her down, replaced the water pump (with a new impeller in the back up pump), and still had no cooling. I disconnected the intake hose from the strainer & blew a bit of air into the hose, which seemed to cure the problem.

Everything worked nicely for 4 or 5 more outings.

Last night we were out & sailed into flat water before starting the motor. I was tired & didn't check for water burping from the exhaust. A few minutes later I got overheat alarms & shut down the motor. Sailing into my slip was extra fun. We secured the boat & went home.

This morning, I went to the boat & inspected my strainer. It's completely clean. I have good water flow when I removed the drain plug & the top cover. I started the motor & all seems OK.

Is this a case of user error/ignorance? Should I be doing something different?

Or, is this more likely a plumbing/mechanical thing I can fix? Any ideas on how to proceed?

Thanks!
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Old 29-06-2022, 11:59   #2
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Re: Intermittent loss of cooling

Hi Chuck.

My first guess would be you're losing prime when sailing and the boat heeled over.

I would look at the level of the strainer, water pump and other parts of the cooling system compared to the water line of the boat, both when heeled over and not.

Or, there's a leak or loose connection in the system allowing air into the lines and again losing prime to the pump.
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Old 29-06-2022, 13:51   #3
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Re: Intermittent loss of cooling

Methinks you should check the basics first.

The hoses from the ocean to the engine's raw water pump MUST BE of wire wound construction, or they will collapse under pump suction. The water strainer must be air tight, or air will enter and cause no water flow.

I've seen worn shaft seals on raw water pumps allow air to enter the pump when running, but they will not leak water when the engine is off. Might be pump rebuild time.

How old is the exhaust elbow? More than 5 years makes it suspicious, as internal rust will restrict water flow. Next remove and clean / test the thermostat and inspect all raw water hoses for condition. Remember, hoses can look fine on the outside, but are delaminating internally, blocking water flow.

Your old Yanmar was never available from the factory with fresh water cooling. It's possible that the internal water passages are clogged with rust, and that intermittently allows some water flow. Joe





Quote:
Originally Posted by kayakerChuck View Post
My boat is a 1979 30' O'day, with a raw water cooled Yanmar 2QM15 with about 930 hours. We bought her about 18 months ago. Last season, I added a Groco sea strainer and replaced the raw water hoses. We had no issues. At haul out time, the intake strainer of the thru hull was nearly clogged with Zebra mussels. I replaced the strainer with a mushroom thru hull, thinking that if I had to, I could disconnect the hose inside and use a dowel rod to knock the little Zebra buggers loose.

This season, I've had 2 incidents where I was not getting cooling water. Both times we were returning to the dock after some "spirited" sailing. The first time, we were healing about 20 degrees when I started the motor. No water burping out the exhaust, even with a blip of the throttle. I shut her down, replaced the water pump (with a new impeller in the back up pump), and still had no cooling. I disconnected the intake hose from the strainer & blew a bit of air into the hose, which seemed to cure the problem.

Everything worked nicely for 4 or 5 more outings.

Last night we were out & sailed into flat water before starting the motor. I was tired & didn't check for water burping from the exhaust. A few minutes later I got overheat alarms & shut down the motor. Sailing into my slip was extra fun. We secured the boat & went home.

This morning, I went to the boat & inspected my strainer. It's completely clean. I have good water flow when I removed the drain plug & the top cover. I started the motor & all seems OK.

Is this a case of user error/ignorance? Should I be doing something different?

Or, is this more likely a plumbing/mechanical thing I can fix? Any ideas on how to proceed?

Thanks!
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Old 29-06-2022, 13:59   #4
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Re: Intermittent loss of cooling

I am going to give you a "got you" thing to check that I once saw.

Be sure that hose aren't getting bent by the engine cover being closed

Even if the pump drains on a heel, It should reprime. Is there an air release, if so it the bleed clean and not crusted up with salt?
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Old 29-06-2022, 18:35   #5
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Re: Intermittent loss of cooling

Thanks all.

The hoses are new (2021) the strainer is new (2021), the raw water pump is newish (2019, ~150 hours of use), no pinch points or chance to pinch the hose with the access hatch. The boat has spent its life in the Great Lakes, so no salt.

I did replace the tailpieces on the sea strainer during winter layup. I R&R'ed them this evening. They seemed OK, but it's possible I had a leak.

I'll report back once I sail her a few times.

Thanks!!
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Old 29-06-2022, 18:52   #6
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Re: Intermittent loss of cooling

Remove and drain the hose between the strainer and the pump.
I know it will sound crazy, but bits of previously shredded impellers can often be found in this area, causing intermittent mystery overheat situations that magically disappear, only to resurface at some other (more inappropriate) time.
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Old 30-06-2022, 05:32   #7
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Re: Intermittent loss of cooling

You could also check the heat exchanger. Ours coped fine when trundling around even when run for a while, but 'randomly' overheated with higher demand.
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Old 30-06-2022, 06:56   #8
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Re: Intermittent loss of cooling

One interesting trick that's helped me in the past.
At the hardware store get a 'drain blaster'
Attach it to a garden hose and insert it into the raw water thruhull and turn on the pressure half way.
This is a quick test that can help reveal or pinpoint many of the issues above.
If there's no immediate flow through at least to the pump intake ftg then loosen each hose clamp one at a time to help locate the obstruction.

C
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Old 30-06-2022, 07:03   #9
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Re: Intermittent loss of cooling

Does this system have a heat exchanger? Twice I have found the lack of water flow to be obstructed by pieces of the pencil zinc on the exchanger. First time was immediately after I bought the boat and second time was when I waited too long to check it.
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Old 30-06-2022, 08:41   #10
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Re: Intermittent loss of cooling

Quote:
Originally Posted by Noisykate View Post
You could also check the heat exchanger. Ours coped fine when trundling around even when run for a while, but 'randomly' overheated with higher demand.
Please read the entire post before responding... It's a raw water cooled engine, no heat exchanger.
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Old 30-06-2022, 11:03   #11
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Re: Intermittent loss of cooling

I've had similar experiences which make me check for water flow every time I start an engine.

Air inleakage to the strainer after maintenance. Solved mid-ocean by generous application of silicone caulk to cover, then strainer replacement.

Inlet fitting plugged with wood chips, solved by hooking hose to dock hose and applying dock water pressure.

Grooves worn in pump cover plate so that pump lost its prime. Solved mid-Transpac by reversing cover plate, then pump replacement.
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Old 30-06-2022, 16:52   #12
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Re: Intermittent loss of cooling

Now just where were those articles about electric motors?
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