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Old 18-12-2011, 23:09   #1
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Yanmar cooling problem

Hello everyone.........I have a Yanmar 4lha-stp/-stzp running a Mercruiser Bravo 2 leg. I am having a problem drawing sea water through the big filter box with the basket insert. The sea water pump is fed with two supplies one being a large through hull supply with a sea cock this goes via the large filter canister and the second a much smaller supply which gravity feeds water in from the leg, these two pipes meet at a tee and go to the suction side of the pump. I am getting flow as the sea water pump is drawing its supply from the smaller gravity pipe but wont suck from the through hull fitting into the filter canister. The boat is pretty new to me so I cant say I have watched water pour into the filter box. I have checked the rubber seal under the clear plastic lid and all looks good and I have checked to make sure the white plastic insert strainer is not fouling the lid. I have disconnected the return pipe where it enters the exhaust and there appears to be plenty of water. The large through hull fitting may have a partial obstruction maybe? Any suggestions? Motor is in great condition only having done about 100 hours. thanks

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Old 19-12-2011, 06:44   #2
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Re: Yanmar cooling problem

Welcome, Please up date your profile so we know where you are.

First I think you have a good idea what the problem is. I would check the thru hull for obstructions. It is amazing how fast things grow.

That derelict boat was another dream for somebody else, don't let it be your nightmare and a waste of your life.
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Old 19-12-2011, 07:24   #3
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Re: Yanmar cooling problem

It could be anywhere in the cooling cct. Start with the obvious and easy things first, such as the through hull and hoses and filter. Did you remove the filter basket? If not remove the basket and check for sea grass, muscles and other crud in the input hose and in the through hull itself. Good luck.
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Old 19-12-2011, 07:50   #4
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Re: Yanmar cooling problem

Have you checked the pump impeller? Could be that enough is left of it to suck from a smaller tube, but not enough for the bigger one.
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Old 19-12-2011, 09:19   #5
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Re: Yanmar cooling problem

Since the engine is probably new, I'm assuming the stern drive is new too. The bravo 2 comes with its own cooling water connections for the raw water pump. Normally those are the only cooling connections for the engine.. I'm guessing the thruhull and strainer was for the old engine / outdrive.

I think it was done that way with the bravo 2 to insure water delivery to the engine when on plane. I'm betting (I bet a lot is seems) the stern drive has slots/strainer in the stern drive water pickup.

Me I might repipe the Bravo 2 connection to the inlet side of the strainer. Though check with the engine / stern drive manufacturer first, as the old strainer might not even be needed now.

From a hydraulic standpoint water will always seek the lowest pressure path in a parallel piped system. So the water will always flow via the stern drive, due to the higher pressure drop of the strainer.
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Old 23-12-2011, 22:23   #6
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Re: Yanmar cooling problem

Thanks everyone for your replies. I am going to the boat shortly and will be checking all the points suggested to me. I will post the outcome ...good or bad. Have a great x-mas.

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cooling, yanmar

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