Outboard cooling system - SailNet Community

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Go Back   SailNet Community > On Board > Gear & Maintenance
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  #1  
Old 05-03-2006
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Outboard cooling system

I have a 1995 Johnson 6hp sailmaster. Just installed new impeller. Trouble is the motor weeps fine until it gets warm then the flow stops. If I shut the motor off and restart it right away she weeps for a few minutes then the cycle repeats. Is this normal? Any help greatly appreciated. Thanks.
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Old 05-03-2006
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This is not normal, the "telltale" weep of the cooling flow is there to let you know that the pump is working. That flow should not be affected by the thermostat directly.
Assuming you are in Salt water:
Your tube to the telltale could be partially encrusted with salt, and as the water warms up expansion pinches off the flow (much as your bathroom taps "slow down" when hot water gets through). Also, perhaps with the thermostat closed initially there is enough pressure to push past the salt, and as the thermostat opens pressure to the weep drops and can't get past the blockage.
The loss of the weep telltale doesn't necessarily mean the impeller/pump is shot, but now you have no indication either way.

Remove the tube, ream/clean it out, clean out the port in the weep hole and check it again. It sounds like a fresh water flush wouldn't hurt either.
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DId you check the water inlet grills and the passage to the pump? They could be clogged with crud and closing off as it runs. Was the pump housing smooth where it meets the impeller? Why did you change out the old impeller? To repair this problem?
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Old 05-04-2006
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yes i changed the impeller to repair this problem.housing looked o.k. i will follow some of "faster's" recomendations this afternoon, thanks everyone.
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run the engine for a while in a mix of household radiator cleaner (for central heating systems) this will break down the scale and make the cooling system work again.
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Take out and clean the thermostat and check it is not stuck open! Note that the thermostat is spring loaded. This works as a pressure valve. At high rpm the waterpressure from the pump push away the thermostat water by-pass and the engine emp should go DOWN! Put your hand on top of the engine, rev it up to above 200 rpm and check. If the temp does not drop about 10C you do not have enough waterpressure. In that case the problem may be a rubber grommet for the water tube where the water enters the cylinder block. In that case the block has to be lifted off the leg. There is even a possbility of exhaust leakage at port side of the engine due to defect gasket at the exhaust cover and a partly blocked cooling channel. If You are not afraid of a bit of work, by a power head gasket kit and change gaskets!
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o.k. this is what i did . filled 55 gal drum up to inlet port with h2o added lime and scale remover and ran engine. yes this worked, thanks everyone
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