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Old 31-07-2009, 00:17   #1
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Yanmar Pump Problem

Hi I have an 18 hp yanmar '89 model, is this a 2G? Anyway problem with it is whenever it is taken out of the water the water pump won't pump on reentering the water. The pump has to be stripped down and reassembled, sometimes it won't work until the impellor is replaced, but the old impellor still looks fine. The Yanmar is connected to a sail drive unit. It's so frustrating any ideas please...

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Old 04-08-2009, 19:31   #2
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I have the same problem with my 3YM20. The raw water pump is above the waterline and it doesn't self prime very well. I found that a bit of silicone grease (Dow Corning 33 -- won't harm rubber) applied to the inside walls of the pump housing is enough to help it self prime. Once there is water in the pump it works fine.

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Old 04-08-2009, 19:42   #3
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Does your saildrive have a valve on it for the raw water.

Try closing it before you haul out.
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Old 04-08-2009, 20:13   #4
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I'm not a diesel expert but it seems like closing the raw water intake would indeed go along way to holding the prime on the engine.
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Old 04-08-2009, 20:24   #5
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The raw water pump on a 2GM20F sits pretty low on the engine and is most likely on a sail drive application below the water line. Assuming no leaks on your intakes lines, how far above the waterline is your sea strainer located?
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Old 04-08-2009, 20:39   #6
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We have a similar problem - here is how we solve it.

1 - Close the raw water valve (should be located on the port side of the tranny). If you are out of the water for a long period this may not work 100%, so on to step 2

2 - Open the sea strainer and start pouring water in while starting the engine (on our Yanmars it takes about a quart), close the strainer and WATCH for water to eventually start shooting out with the exhaust. Sometimes this can take a few minutes. Repeat as necessary.
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Old 22-08-2009, 21:58   #7
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Thanks Guys you have given me some options that I will look into
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Old 23-08-2009, 09:26   #8
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Scarecrow - When you had the pump apart, was the back plate or cover plate scored / worn much?

Mine worked OK, but I used to have to close the seacock, while sailing, or it would lose it's prime as well. After I reversed the scored cover plate, it works better, and I never have to close the seacock now.

I'd bet that if yours is worn somewhat, you could improve it's efficiency, by replacing the worn parts (or flipping the cover over). It may be enough of a gain, to make a difference!
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Old 25-08-2009, 19:41   #9
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Check the raw water strainer

Check to be sure that your raw water strainer isn't leaking slightly and sucking air. Had this problem recently, and the raw water strainer had a bad gasket on the bottom, and was allowing it to suck enough air to not prime. If the strainer is above the water line, even if you pull the boat out of the water, there should be enough water in the line from the strainer to the pump to allow it to prime. Be sure to check the pump for even a slight leak, as if all the water drips out, it will of course not be primed.

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