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Thread: Yamaha 40 outboard Jet (2 stroke) water cooling help needed

  1. #1
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    Default Yamaha 40 outboard Jet (2 stroke) water cooling help needed

    I have an older 2 stroke Yamaha 40 jet. The motor runs great but I seem to have a restriction in the cooling water flow. Last year while on the river I had some sand get in the cooling hose and was able to flush it there and get back up river. After that, I will get some water flow, then it may stop peeing and I would shut down the motor and let it cool. Once cool, the motor would pee again and then slowly stop as the motor got warmer. in the end I was making lots of short runs with a lot of bank time.

    If you have any thoughts or ideas on what the issue or fix is, I would love to hear them.
    Thanks.

  2. #2
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    Water pump

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    Replace the water pump impeller. When the motor picked up that sand, in all likely hood, the impeller seized in the housing while the shaft/hub continued to turn, so you have the rubber portion "loose" on the hub portion. That is , if it is not worn out anyhow.

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    Had the same problem with my Yamaha OB jet. Pulled out the thermostat problem solved.

  5. #5

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    I ran the same motor (prop) for years, and those sound like classic water pump issues. I'm betting some of the sand got as far as the impeller and cob was raised. It's a small job to change out yourself. Lots of sources for online instruction if you haven't done it before.

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    I pulled the thermostat and there was some small rocks keeping it open. I tested the thermostat and it seemed to function properly. I'm not sure if that will do it or not, buy I ordered a pump replacement kit and will give replacing it a shot. Thanks for the replies.

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    Member hogfamily's Avatar
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    Get a chrome pump. They will last much longer.

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    Quote Originally Posted by peaceman View Post
    I pulled the thermostat and there was some small rocks keeping it open. I tested the thermostat and it seemed to function properly. I'm not sure if that will do it or not, buy I ordered a pump replacement kit and will give replacing it a shot. Thanks for the replies.
    A thermostat that is blocked open would have the opposite effect - not allow the engine to heat up properly as it would not restrict the flow of water enough. The water pump is the issue regarding the over heat/ lack of flow.

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