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  1. #1
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    1989 Mercury 175 cooling question

    Good evening all -

    1989 Merc 175, I am having an odd cooling issue. All the years I've had it and run it on the hose it always had good flow out of the telltale and both heads would be consistently cool.
    All of a sudden, flow is poor, I'm getting no water out of the top of the heads unless I rev it up and the right head is getting hotter than the left.
    I thought it was the pump so it has a new Mercury pump kit, no change. I do not run the T-stats in the heads, I have restrictors in their place and no tiny "pee hole telltale", it runs out of a 5/16 (maybe 3/8) hose out the back. It is plumbed all stock, no changes with that.
    It is reading between 5-10 psi on the gauge, the poppet valve isn't leaking and was replaced a couple years ago.

    It was good forever, all of a sudden this is happening. Any ideas out there??

  2. #2
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    What about out on the lake. Any change in running temp or water pressure

  3. #3
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    If u got new pump kit , look at poppit again, mite b half stuck ,unless sucked up bunch sand or piece of gasket/pump lodged sumwere. Seems like to much pressure at idle.

  4. #4
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    I haven't had it out yet, has me a little nervous with the way it is acting now. And I have no temp gauge or warning buzzer, just the PSI gauge.
    I will open up the poppet and see if anything is out of the ordinary with that.
    Maybe bring it to the ramp and run it on the trailer in the water and see what things look like.

    Thanks fellas!

  5. #5
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    Like merc said there is probably a blockage starting. Would look at adding a temp gauge too, they are much cheaper then rebuilding a motor

  6. #6
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    Does the sender for a temp gauge go in the starboard head and look like a wire with a spring at the end? I think I I have one kicking around and a maybe a gauge too. Would not hurt to finally hook it up as you are 110% correct 89Talon!

  7. #7
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    Yes i do believe it goes in the starboard head

  8. #8
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    Quote Originally Posted by noots View Post
    Does the sender for a temp gauge go in the starboard head and look like a wire with a spring at the end? I think I I have one kicking around and a maybe a gauge too. Would not hurt to finally hook it up as you are 110% correct 89Talon!
    that's an "over temp" sensor (one wire) that will set tha buzzer off.. goes in tha starboard head.. a temp gauge sensor will have two wires, one sender (usually tan or tan/blue) goes ta gauge anda ground.. goes in port head....
    Last edited by tlwjkw; 06-26-2019 at 06:49 AM.

  9. #9
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    So I pulled the poppet out and sure enough a small pebble fell out. Cleared that out, put it back together and BOOM, consistent temperature in both heads and good water flow out of the top of both heads. I would’ve never thought something like that would get stuck in there considering I do have a screen on the water pickup, but, guess anything is possible.
    i have to guess maybe that pebble got jammed in the diaphragm or spring somehow.
    Scream and Fly to the rescue again!
    Thanks everyone.

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