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Thread: Yamaha 50 2 stroke overheating at idle only

  1. #1
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    Default Yamaha 50 2 stroke overheating at idle only

    I recently replaced the thermostat and water pump. The engine overheats at idle but anything above idle is fine. What did I do wrong?

  2. #2
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    Did it do that before you replaced the thermostat and water pump? How is it pissing at idle?

  3. #3
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    It did not. Pissing strong at all times.

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    Is it possible that you have the blades of the new impeller twisted the wrong way?
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    That’s certainly possible. I guess I can reverse it and see what happens.

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    Quote Originally Posted by Rubberhead* View Post
    Is it possible that you have the blades of the new impeller twisted the wrong way?
    Would they not correct themselves? I have no clue, but have thought about this before.

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    Quote Originally Posted by JOHNSON View Post
    Would they not correct themselves? I have no clue, but have thought about this before.
    likely destroy itself first....turn the shaft clockwise when pressing the housing down

    makes no sense that it's pissing fine at idle but the alarm comes on?

  8. #8
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    OEM thermostat? Some of that aftermarket stuff does not fair well especially with Yamaha. If it’s pissing strong it shouldn’t be the impeller imo, as water is flowing i.e. the impeller is spinning and creating positive head pressure. My guess is the thermostat or temp sensor. In case you still want to see if the impeller is aligned correctly don’t just reverse it as you may have it correct. Spin the motor with the lower unit off. The impeller fins should be aligned in the opposite direction as the direction the drive shaft spins.
    Last edited by cam1195; 12-04-2019 at 02:06 PM.

  9. #9
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    1) what was it doing before you installed new parts?
    2) drop your thermostat in hot water to make sure it's working
    3)Just because it's peeing strong doesn't mean you don't have a blockage in the powerhead. To eliminate the water pump from the equation, hook your garden hose up straight the watet pick up tube in the midsection and report back whether that fixes the problem or not.
    Last edited by tman; 12-04-2019 at 02:19 PM.
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  10. #10
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    Shit, don't sound like a problem to me, just cut the damn thing off at idle. I wish my boat problems were that simple.
    ..

  11. #11
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    Don't rule out bad temp sensor....shoot each of the three holes with a laser gun to see what the temps are. Will also isolate the blockage if there is one.

    If it is a salt water motor, you would be amazed at what the cooling passages can look like even if flushed religiously. The coolant passages on my f250s actually corroded all the way through and I was getting peanut butter in my chocolate on both of them.

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    Quote Originally Posted by tman View Post
    ...hook your garden hose up straight the watet pick up tube in the midsection and report back whether that fixes the problem or not.
    Don't think I've ever seen a Yamaha 2 stroke with one of those. If that piece you're trying to describe is what i think it is.

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    Thanks for the replies. I’ll try a few things and report back.

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    Quote Originally Posted by willyworm View Post
    Don't think I've ever seen a Yamaha 2 stroke with one of those. If that piece you're trying to describe is what i think it is.

    Sent from my SM-G930V using Tapatalk
    im describing the pickup tube that mates to the water pump housing. NOT the saltwater flusher tube that some models have.
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    Quote Originally Posted by FishSticker View Post
    Don't rule out bad temp sensor....shoot each of the three holes with a laser gun to see what the temps are. Will also isolate the blockage if there is one.

    If it is a salt water motor, you would be amazed at what the cooling passages can look like even if flushed religiously. The coolant passages on my f250s actually corroded all the way through and I was getting peanut butter in my chocolate on both of them.
    We had a 250 corrode through the block and started shooting raw water into the flywheel, it didn't like that for some reason.

    The marina guys swore they were rinsing the motor and that you didn't have to so far up the river....

    OP, is it alarming or water gets hot or both? Do you have temp gun? Shoot block to find blockage?

    Was the old impeller really beat up and could be a piece stuck somewhere?

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    My yami 2 stroke would overheat when slow trolling for kings- it was the poppet valve- does your motor have one?

  17. #17
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    its a water pressure problem if idle only,
    if it didn't do it before your work.....drop it down and look at the impeller,
    plate underneath it, O-rings, alignment tube, etc,
    If that doesn't work, take the thermostat out of it and see what it does and get back to us.

  18. #18
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    Quote Originally Posted by Bad Habit View Post
    My yami 2 stroke would overheat when slow trolling for kings- it was the poppet valve- does your motor have one?
    This. Poppet maintains water pressure at low rpm

  19. #19
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    Coming back to this. From the diagram, it does not look like it has a poppet valve. I am going to try some of these suggestions today and report back.

  20. #20
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    Poppet valve is built into the thermostat on the smaller engines

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