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Old 27-04-2012, 11:49   #1
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How to Prime Raw Water System on Yanmar 27hp

I recently broke the water pump belt on my engine. I have replaced the belt and run the engine but it doesnt suck in any water into the strainer. I filled the strainer from the deck hose and the pump seems to be working fine as it sucks the water from the strainer and discharges out the exhaust. I run it like this for several minutes then try to fill the strainer to the top and quickly put the lid back on, but it just sucks dry and no water comes in from the seacocks...

Any ideas???
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Old 27-04-2012, 11:52   #2
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Re: How to Prime raw water system on Yanmar 27hp

Is the strainer above the water line? Check for clogs at the seacock (or is it closed?). Check for air leaks high in the system causing a lock. If the pump ran dry it may have destroyed its impeller, go ahead and change that now if you can.
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Old 27-04-2012, 12:22   #3
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Re: How to Prime raw water system on Yanmar 27hp

Impeller vanes can take a set and don't press well enough against the pump body. Also old impellers develop tiny cracks in the tip of the vanes which let air past. So replace the impeller first.

Also check that the suction hose from the seacock to the strainer isn't collapsing due to old age and that the seacock or its external strainer isn't plugged. Make sure that the injection elbow isn't plugged. Take off the hose and poke inside it with a screw driver. If you get a bunch of scale, replace the elbow.

When all of that is ok and if it still won't prime then remove the discharge hose to the heat exchanger, run the engine until water comes out, connect the hose. Sometimes (with an old impeller) you even have to remove the hose on the outlet of the heat exchanger and let water blow out there before you reconnect it to the vented loop.

David
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Old 27-04-2012, 12:30   #4
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Re: How to Prime raw water system on Yanmar 27hp

buy used water. the bottled stuff is better as it has less negative ions in it. use a turkey baster as it will fit into most hoses.

you actually need to make sure your sea strainer is below water level. make sure it is clean. make sure your intake system is below water level.....make your sea strainer BELOW the waterline.

i hope you found the first thing i wrote funny and smiled at it. this is not a new problem.
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Old 27-04-2012, 14:19   #5
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Re: How to Prime raw water system on Yanmar 27hp

If its a 3gm30, I doubt it will prime itself all the way from the strainer. Mine won't because the line from the strainer rises above sea level on its way to the engine. I simply remove the sea water hose from the strainer, use the garden hose to fill the seawater line (priming it) forcefully, then quickly reattach the seawater hose to the strainer. ps.. I have only had to do this after cleaning the strainer and inadvertantly drained the seawater hose supplying the engine.
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Old 28-04-2012, 08:06   #6
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Thanks to all, your responses prompted me to think outside the square and I simply started the engine unbolted the strainer off the bulkhead and held it below the water line and after a bit of gurgling and spluttering it started drawing water into the strainer and continued to do so when I bolted it back up....

I also know a lot more about my cooling system now too.....

Thanks again, Koh Racha awaits
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Old 05-05-2012, 15:33   #7
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Re: How to Prime raw water system on Yanmar 27hp

Quote:
Originally Posted by Prashanti View Post
Thanks to all, your responses prompted me to think outside the square and I simply started the engine unbolted the strainer off the bulkhead and held it below the water line and after a bit of gurgling and spluttering it started drawing water into the strainer and continued to do so when I bolted it back up....

I also know a lot more about my cooling system now too.....

Thanks again, Koh Racha awaits
Glad it's working........but,

The pump should pull thru the strainer even it's above the waterline. If there are no leaks and the impeller is new, I would guess the cover plate and/or cam on the pump is worn. Might be time to examine it carefully and maybe buy some spare parts. I have (2) 3GM30s and (4) pumps. When a pump acts up, I rotate with a spare and rebuild the one taken off for the spare parts bin.
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