Overheating

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    Posted: 13 Dec 2019 at 7:17pm
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My 15hp Yamaha 2stroke is overheating. When cold a good stream of water exits the teltail but when the motor warms the teltail water is very hot and after a short time stops altogether.
My thoughts are a faulty thermostat but I am no expert.
Any thoughts appreciated.
I am on Waiheke. Do you know of anyone on the Island that repairs outboards.
Thanks
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Post Options Post Options   Likes (0) Likes(0)   Quote RogueOne Quote  Post ReplyReply Direct Link To This Post Posted: 01 Feb 2020 at 2:28pm
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It could be a blocked thermostat. There is a by-pass which allows some water to circulate when the thermostat is closed.

Many of the Yamahas have an anode in the water jacket under the cylinder head. As it dissolves it can clog the water passages.

When the thermostat is open, it obviously flows from the pump, through the block and heads via the thermostat, and into the exhaust. If the passages in the block and heads are blocked or the thermostat is faulty (or both) then the cooling water can't get through there and keep things cool.

Check the thermostat to see if it is gummed up and not opening then check the passages. You can pull the thermostat out and replace the cover to see if allowing water straight into the head keeps things cool.
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