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Old 28-05-2022, 09:46   #1
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Check Yanmar water pump

I've removed the water pump on my 3GM30F on my way to removing the head. Prior to this work, I've not had issues with overheating nor has there been seeping from the pump.

I'm wondering what I should check on this pump before re-installing it. There doesn't appear to be any play in the bearings, but they seem to be snug. I can turn the shaft by hand, but it stops turning as soon as I stop moving it. Normal?
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Old 28-05-2022, 14:26   #2
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Re: Check Yanmar water pump

Totally normal. It's a vane pump, and you're turning the rubber vanes against the flat side inside the pump that compresses them and squirts out the water. If it turned freely, then you'd have a problem.

Consider taking the cover off and getting aquainted with your pump. The vanes pick up the water on one side, run it around the bottom of the pump, and then squeeze it out the discharge on the other side.

Here's Jabsco's Youtube on how they work:
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Old 28-05-2022, 14:50   #3
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Re: Check Yanmar water pump

Actually it's an impeller pump. A vane pump is different and is a positive-displacement pump, that will create significant pressure. An impeller pump is not positive displacement, meaning it can just spin against a closed system like a valve without immediate damage.
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Old 30-05-2022, 07:36   #4
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Re: Check Yanmar water pump

By impeller pump do you mean a centrifugal pump? Jabsco uses the term "impeller pump" to mean a soft impeller vane pump, as in the Youtube I posted. They are positive displacement, self priming, and can be quickly destroyed by being run dry. They are common in raw water supply for cooling. Centrifugal pumps are not self priming or positive displacement, can be run dry, and are common to bilge pumps.

There are also vane pumps, with rigid vanes that slide in slots in the hub. I'm familiar with them as priming pumps on a fire engine, but have not run across one on a boat.

What Jabsco calls an impeller pump could also be called a "soft vane pump," I guess.

Damned confusing for after only one cup of coffee.
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