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Go Back   SailNet Community > On Board > Gear & Maintenance > Engines > Diesel
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Diesel This is a forum dedicated to diesel engines and their applicable accessories.


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Old 03-10-2014
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seawater system

The seawater strainer placed above sealevel and on the highest point on the seawater system on our Yanmar 3gm30f is empty when the engine is not running.

Is this normal ?
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Old 03-10-2014
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Re: seawater system

I don't know. Mine is below sea level and stays full of water all of the time.
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Old 03-10-2014
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Re: seawater system

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Originally Posted by carlager View Post
The seawater strainer placed above sealevel and on the highest point on the seawater system on our Yanmar 3gm30f is empty when the engine is not running.

Is this normal ?
Doesn't sound 'normal' to me.. it also means your impeller must run dry on every startup for a moment.. Is there room to relocate it? Ours is also below waterline and always 'primed'.
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seawater system

The impeller is on the other side of the strainer and does not run empty
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Re: seawater system

Are you saying the strainer is after the impeller? If the impeller is (properly) downstream of the strainer then it's pulling air for a bit until the system is once again flooded...
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Old 03-10-2014
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Re: seawater system

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Are you saying the strainer is after the impeller? If the impeller is (properly) downstream of the strainer then it's pulling air for a bit until the system is once again flooded...
Faster is absolutely correct the impeller will run dry for a short period. Even if it is downhill from the strainer to the pump and that section of hose is full of water, the air in the empty strainer will get sucked through the impeller.
That impeller is going to have a very short life and failure will be sudden. When an impeller fails you have a few minutes at most to notice the overheat and shut her down or serious damage will occur.
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Old 03-11-2014
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seawater system

You are right. The strainer should be full when the engine is not running. Greased the O-ring on the lid to the strainer. Now there is vacuum when the engine is not running and water In in strainer
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Re: seawater system

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Originally Posted by carlager View Post
You are right. The strainer should be full when the engine is not running. Greased the O-ring on the lid to the strainer. Now there is vacuum when the engine is not running and water In in strainer
Glad you got it worked out. I'd recommend you pull that impeller for a close inspection and if possible reposition the strainer as low as you can get it, preferably below waterline (difficult in many sailboats).
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Re: seawater system

Could be an air leak at the strainer itself, or one of the hose connections. Clear seawater lines are great for detecting air leaks. You can see the bubble constantly flowing through.
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Old 03-13-2014
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Re: seawater system

I agree with minnewaska there must be a loose fitting or opening somewhere in the line that is allowing for the vacuum in the line. Does it immediately empty, or does it take its time? Does that water run back to the engine or through the exhaust line? Speaking of which, you may want to check the exhaust line and make sure that it doesn't exit below the strainer. That would create the vacuum issue you are experiencing.


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