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Old 05-03-2020, 13:41   #1
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Yanmar 3GM30F cooling system problem

I'm having a problem with a Yanmar 3GM30F. I had the water pump rebuilt- the bearings were shot. After the rebuild, I reassembled everything, fired up the engine and it worked just fine. Good flow of water from the exhaust, smooth running, no overheating alarm.
I let it run for about 5 minutes, shut it down and replaced the raw water hose with a hose into a bucket of antifreeze. Fired it up again and... nothing.
I tried a few different things, then took everything apart again and examined the pump. It seems fine... the impeller spins when I turn the pulley, no hoses seem to be collapsing, nothing looks different.
I'm stumped- I don't understand why it would work well until being shut down and then just quit.
Has anyone else encountered this? I'd sure appreciate hearing about how I can fix this pretty frustrating problem.
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Old 05-03-2020, 21:49   #2
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Re: Yanmar 3GM30F cooling system problem

Have you bled the engine? The shut down might have been coincidental to the amount of time it took for an air bubble to work its way through. If it's not that, then I ain't got nothing more helpful.
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Old 05-03-2020, 21:57   #3
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Re: Yanmar 3GM30F cooling system problem

Yes, pour some antifreeze down the hose before you put it into the bucket.
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Old 06-03-2020, 03:33   #4
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Re: Yanmar 3GM30F cooling system problem

Greetings and welcome aboard the CF, Andrew.
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Old 06-03-2020, 05:55   #5
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Re: Yanmar 3GM30F cooling system problem

Shut the thruhull, and pour antifreeze into your water strainer . No need to disconnect any hoses
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Old 06-03-2020, 06:29   #6
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Re: Yanmar 3GM30F cooling system problem

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Originally Posted by chris mac View Post
Shut the thruhull, and pour antifreeze into your water strainer . No need to disconnect any hoses
Wait, I'm confused. Why is he putting antifreeze in the raw water (sea water) side? The coolant is in a closed system.
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Old 06-03-2020, 06:31   #7
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Re: Yanmar 3GM30F cooling system problem

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Wait, I'm confused. Why is he putting antifreeze in the raw water (sea water) side? The coolant is in a closed system.


To prevent the seawater side from freezing.
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Old 06-03-2020, 06:40   #8
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Re: Yanmar 3GM30F cooling system problem

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Have you bled the engine? The shut down might have been coincidental to the amount of time it took for an air bubble to work its way through. If it's not that, then I ain't got nothing more helpful.
I haven't... Someone else mentioned a possible "air lock", too. I'll have to see what I can find in the way of troubleshooting info for that.
Thanks for the suggestion!
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Old 06-03-2020, 06:41   #9
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Re: Yanmar 3GM30F cooling system problem

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Greetings and welcome aboard the CF, Andrew.
Thank you. Good to be here!
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Old 06-03-2020, 06:45   #10
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Re: Yanmar 3GM30F cooling system problem

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Shut the thruhull, and pour antifreeze into your water strainer . No need to disconnect any hoses
Thanks! That's a good suggestion, I'll do that when I can get fluid to move through the system again.
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Old 06-03-2020, 07:54   #11
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Re: Yanmar 3GM30F cooling system problem

Are you sure the hose wasnít sucked down to the bottom or side of the container?

Iíve had that happen a few times, the cure is to notch the end of the hose.

As far as an airlock, Iím not buying it. The raw water pump is a semi-displacement pump that will move fluids (air is a fluid) when itís turned.
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Old 06-03-2020, 09:54   #12
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Re: Yanmar 3GM30F cooling system problem

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Are you sure the hose wasnít sucked down to the bottom or side of the container?

Iíve had that happen a few times, the cure is to notch the end of the hose.

As far as an airlock, Iím not buying it. The raw water pump is a semi-displacement pump that will move fluids (air is a fluid) when itís turned.
It's possible that the hose blocked itself, but when I put it back together with the raw water hose attached and the seacock open, it still wouldn't pump anything. Vexing.
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Old 06-03-2020, 10:04   #13
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Re: Yanmar 3GM30F cooling system problem

Have you taken the outlet hose off of the seawater pump to see it it pumps any water?
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Old 06-03-2020, 11:24   #14
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Re: Yanmar 3GM30F cooling system problem

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To prevent the seawater side from freezing.
Ah, now I know why I don't live in areas where it freezes!

Andrew, did you check the pump impellor to make sure nothing got damaged during those 5 minutes you had it on? If everything is running but the pump is not sucking, the condition of the impellor seems like a good thing to verify.
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Old 06-03-2020, 12:08   #15
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Re: Yanmar 3GM30F cooling system problem

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Have you taken the outlet hose off of the seawater pump to see it it pumps any water?
Not yet- it was the end of the day so I buttoned everything back up and started the troubleshooting phase, but that's a good idea and it will be next. Thanks!
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