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Old 09-04-2011, 00:47   #1
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Yanmar 3ym30 Fresh Water Pump: Seal Leaking

Have a newish ( about 4 years old) 3YM30 with 260 hours on it.
Fresh water pump seal is leaking.
Engine has done 600 nautical miles in the last three months. Regularly serviced, has Yanmar coolant, alternator belt is not too tight, pump bearing appears intact.
Anyone else have this happen? I would not expect this on a low hour new engine.
I plan to pull the pump, does anyone know if the seal can be replaced, or do I need a new pump?
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Old 09-04-2011, 03:57   #2
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Re: Yanmar 3ym30 fresh water pump seal leaking

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Old 09-04-2011, 05:22   #3
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Re: Yanmar 3ym30 fresh water pump seal leaking

Check carefully that the water is not simply leaking at one of the hose connections. I assume the water is coming out of the weep hole and therefore the seal is suspected.

Had to put a fresh water pump on my 3gm30f last month. On mine the bearing was definitely bad and it's not a design that can be rebuilt. The impeller is crimped on the shaft just as an automotive pump. It wasn't hard to replace the pump besides having to crawl into the cockpit locker on my backwards engine.

The seal on mine is actually a ceramic and carbon construction that also serves as the thrust face. Before installing, it's requiring to be placed in water to soak for a while. This is to prevent a dry squeal at initial start-up.

The unconventional seal design and impeller construction made mine impossible to rebuild at home.
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