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#575152 - 05/17/21 06:33 PM Yamaha L4 3.0 stern drive coolant water blockage  
Joined: May 2021
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rdoty Offline
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rdoty  Offline
Warrant Officer

Joined: May 2021
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Lakewood, CO
I'm in the process of restoring an Ebbtide 170 XS with a Yamaha L4 3.0 stern drive. I finally got the motor running today but discovered that there is no coolant water. By process of elimination, the problem seems to be some kind of blockage within the stern drive unit itself. I've disconnected the hose that runs from the transom mount to the seawater pump and the hose is bone dry although the flusher is supplying plenty of water. I've got all the Yamaha manuals, engine and stern drive, but there's nothing showing the coolant water path through the lower unit and transom mount so I have no idea where to look for the blockage. Does anybody have a clue as to what or where the blockage could be and do I need to remove the lower unit to access the coolant water path?

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#575153 - 05/17/21 07:45 PM Re: Yamaha L4 3.0 stern drive coolant water blockage [Re: rdoty]  
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WaterWing Offline
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WaterWing  Offline
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Chicago
My suspicion would be the impeller. In Mercruiser the impeller draws water into the water pump. I think Yamaha should have the same design. The impeller is located in the lower part out the outdrive.


2001 Larson SEi-230 5.7 Merc/Alpha1
2013 Ford Explorer
#575154 - 05/18/21 01:04 PM Re: Yamaha L4 3.0 stern drive coolant water blockage [Re: rdoty]  
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rdoty Offline
Warrant Officer
rdoty  Offline
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Lakewood, CO
I understand the function of the impeller in normal operation. The problem is that there is no water available for the pump to pump because there is apparently a blockage somewhere in the lower unit water path. I should be able to fill the engine water circuit with the flusher without the pump being powered. For example, the Engine Service Manual p 5-2 says to install the flusher, turn on water and fill the cooling system until water is discharged from the exhaust port - then start engine. In normal operation, the impeller has to draw water into the system when the boat is in the water i.e. no water pressure into the lower unit inlets.
The only indication of the water circuit within the lower unit in the manuals is one exploded diagram of the transom mount that shows the outlet water tube (which goes to the inlet of the seawater pump) and an internal molded hose and a "water damper seal" and that's it. There is no other reference or part called a "water damper" except in the parts explosion of the lower unit that has a part labeled "damper guide".

#575155 - 05/18/21 01:46 PM Re: Yamaha L4 3.0 stern drive coolant water blockage [Re: rdoty]  
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WaterWing Offline
Admiral
WaterWing  Offline
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Chicago
So you were able to inspect the impeller and it’s still intact? A lot of times they break apart and a rubber fin blocks the flow of water.


2001 Larson SEi-230 5.7 Merc/Alpha1
2013 Ford Explorer
#575156 - 05/18/21 08:52 PM Re: Yamaha L4 3.0 stern drive coolant water blockage [Re: rdoty]  
Joined: May 2021
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rdoty Offline
Warrant Officer
rdoty  Offline
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Joined: May 2021
Posts: 7
Lakewood, CO
Sorry, maybe I wasn't clear. It's not an impeller problem. There's no water getting through the stern drive unit so the water pump has no water coming into it. To clarify, water enters the sterndrive lower unit through slots. A "flusher" that connects to a garden hose is clamped over the openings and provides the cooling water to the pump. The water goes through the stern drive and the transom mount and through a hose that is connected to the inlet of the pump. There is no water in the hose.

#575158 - 05/19/21 05:51 AM Re: Yamaha L4 3.0 stern drive coolant water blockage [Re: rdoty]  
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Dave R Offline
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Dave R  Offline
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Hampton Beach, NH USA
An air leak upstream of the water pump is more likely than a blockage. Even a small air leak will easily prevent the suction from the pump from pulling water. I would look closely at the seals on the water tube and the gasket between the upper gear case and the bell housing.


"Mischief Managed II" 1992 Tollycraft 44 Cockpit Motor Yacht-Twin CAT 3208TA inboards
"Portkey" 2020 North Atlantic Inflatables 10'6" aluminum RIB-Mercury 15HP two stroke
2015 Sea Doo RXT-X
2015 Sea Doo RXT
#575160 - 05/19/21 02:59 PM Re: Yamaha L4 3.0 stern drive coolant water blockage [Re: rdoty]  
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Lou C Offline
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Lou C  Offline
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Long Island NY
I tried to find diagrams of this drive system but they are tough to find. It looks a lot like an OMC Cobra. What I'd do is try to reverse flush your raw water path, disconnect the raw water hose from the impeller housing and put a garden hose in it. Then have someone hold the garden hose in the raw water hose and turn on the water. Next head back to the stern of the boat and see if water is coming out of the outdrive water intakes. If so then there is not likely to be a blockage but if no water, then the water tube grommets inside the drive may be bad. Unfortunately these units are very hard to get parts for, you'd have to split the upper and lower gear housings to replace those water tube grommets.


88 Four Winns 200 Horizon 4.3 OMC
98 Jeep Grand Cherokee 4.0 Six Selectrac
07 Jeep Grand Cherokee 5.7 HEMI Quadradrive II
#575163 - 05/22/21 12:26 PM Re: Yamaha L4 3.0 stern drive coolant water blockage [Re: rdoty]  
Joined: May 2021
Posts: 7
rdoty Offline
Warrant Officer
rdoty  Offline
Warrant Officer

Joined: May 2021
Posts: 7
Lakewood, CO
Well I solved the blockage problem by pushing a 1/4 inch OD tube connected to the end of the garden hose into the lower unit water inlet (take the inlet strainers off). There is a small opening, about 1/2 inch diameter that I can feel with my finger, and I fished the tube up through that opening and in about five minutes it broke through whatever was blocking the path. At first the tube would only go up; about six inches and when it finally broke through it was maybe 8-10 inches. Anyway, now that's done and fortunately I didn't have to drop the lower unit. Not sure what the blockage was - most likely sand - and I'll do a good flush before I reconnect the seawater pump.
The next thing - and I'll do another post - is dealing with the hydraulic trim/tilt pump.


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