Rust Problem, Maybe?

Stringer Guy

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Jun 25, 2014
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My 1979 Seaswirl (OMC 120 HP with Stringer 400) is still overheating. I was wondering if it is even possible that rust could be clogging the manifold. I pulled one of the drain plugs today and brown water came out. Has anyone heard of something like this?
 

Bondo

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Ayuh,.... Welcome Aboard,..... Anything is possible,....

Pull the riser off the manifold, 'n have a look,....

The water has to get In, so a new impeller is important,...
'n water has to be able to get out, so ya, check the riser connections,...
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
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did you replace the raw water pump? on a stringer, I normally replace the whole pump assembly
 

Stringer Guy

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Jun 25, 2014
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I replaced the impeller last year. It pumps water but still overheats. Even after I pulled the thermostat.
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
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pulling the thermostat actually makes it worse because the water is moving too fast. without a thermostat, you need a restrictor plate.

with the boat in the water (on the trailer). disconnect the line from your transom and put in a 5-gallon bucket. you should fill the 5 gallon bucket in about 15 seconds. if you do, you have good flow to your motor. if not, look at your drive/intermediate, etc. for a restriction
 

Stringer Guy

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Jun 25, 2014
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Appreciate the input. Not a lot of local advice. The manifold was packed also so I'm getting some descaler and running it thru the block. I'll let you know what happens.
 

kenny nunez

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Jun 20, 2017
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If you knock out the core plugs and remove the water pump you will be able to get a lot of the slag that is in the block by using a pressure washer or even a garden hose.
 

Lou C

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Nov 10, 2002
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11,803
Normally raw water cooled manifolds and risers have to be replaced in salt water every 5-7 years, but even in fresh water you can get corrosion that clogs up the water passages if the water is corrosive enough. Flushing out the block with the water pump removed it a good idea, if you don't remove the core plugs at least open the engine block drains.
 
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