18HP Johnson Seahorse - Cooling Issues

JohnHP

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Mar 9, 2014
Messages
3
I have a 1965 version Johnson 18HP Seahorse that is not flow cooling water. I took the foot off, checked the impeller, replaced a broke o-ring on the shaft at the pump but still no flow after I re-assembled everything. So I removed the foot again and this time hooked a garden hose with fitting up to the water inlet tube. No water flows it just build up full pressure and shot back out when I removed it... I can locate and take off the thermostat cover and when I did I really didn't see anything in there, it just looked like an open chamber, I poured some water in and it did drain out but Im wondering if the thermostat is gone but even if gone I should still get flow through the bypass, correct?

Am I screwed? If the lines are blocked how would I go about confirming beyond what I already did and then how can it be cleared if it is blocked?

Thanks
 

jbjennings

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Jul 18, 2007
Messages
3,903
Re: 18HP Johnson Seahorse - Cooling Issues

SOme possibilities if you can't get water coming out even with a hose attached to the water tube (you are talking about the copper water tube going up the midsection, right?):

1) impeller vane in the water tube
2) impeller vane in water jacket
3) Crimped water tube grommet under powerhead
4) corrosion blockage---is this a salt water motor??

You should still get water circulating even with the thermostat gone.

You can get to water jackets by removing the exhaust cover, cylinder head, and under the powerhead.
I'd remove the powerhead and check that nothing is in the water tube and that the upper tube grommet is not pinched and clear before removing the exhaust covers and head because they're bad about breaking bolts and the gaskets cost money.
JBJ
 
Last edited:

Will Bark

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Joined
Aug 1, 2010
Messages
1,470
Re: 18HP Johnson Seahorse - Cooling Issues

Have you tried to back flush it; water hose thru the thermostat hole? maybe force what's stopping it up back out. Good luck
 

JohnHP

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Mar 9, 2014
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3
Re: 18HP Johnson Seahorse - Cooling Issues

Thank guys, I did try to back flush but not from the thermostat, I wasn't exactly sure what I was looking at so I was leary of ruining anything but Ill give it a try. Ill also learn more about what it takes to remove the exhaust covers
 

JohnHP

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Mar 9, 2014
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Re: 18HP Johnson Seahorse - Cooling Issues

Update. Thanks for the help, it turns out the thermostat was previously removed so I flushed back toward the pump and the lines were clean. The line going to the discharge was pack solid so I kept filling with water to loosen it and the inserted a PVC cold water facet hose into the thermo port (perfect fit) and flushed with full garden hose pressure, the plug finally dislodged!
 

HighTrim

Supreme Mariner
Joined
Jun 21, 2007
Messages
10,486
Re: 18HP Johnson Seahorse - Cooling Issues

Awesome. Don't forget to replace the t stat.
 
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