1975 searay ford 351 overheating

Discussion in 'Gas Engines' started by Shanerbones, Jul 16, 2018.

  1. Shanerbones
    Joined: Jul 2018
    Posts: 1
    Likes: 0, Points: 1
    Location: Ohio

    Shanerbones New Member

    I hope I am doing this right and posting in the right place i am new to this if not let me know I will gladly remove..... but I have a 1975 searay with a ford 351 and I believe I am running hot. I have changed water impeller and pump housing checked screen for zebra muscles. (Old impeller was perfectly in tact) and have also changed the thermostat. (Which is a 140 degree stat) I have pulled hoses from circulating pump and hoses to thermostat housing and all seem to be flowing water fine. My problem is I am still running around 180 to 190 degrees when under load and running. Soon as I slow down to idle the temp goes up for a second and then slowly cools back off I am stumped and could use some help thanks in advance
     
  2. Sparky568
    Joined: Jan 2017
    Posts: 84
    Likes: 4, Points: 8, Legacy Rep: 10
    Location: Northeast USA

    Sparky568 Junior Member

    Maybe need a little more info. Is this a raw water cooled system or split? I see your in the middle of the country so salt water wouldn’t be an issue but if your circulating water through the exhaust manifolds there could be some corrosion blocking passages. My other question is if you’re coming off plane and dropping to low idle one would expect the temp to spike for a bit. Try coming off cruise speed more slowly over the course of a couple minutes.
     
  3. missinginaction
    Joined: Aug 2007
    Posts: 742
    Likes: 62, Points: 28, Legacy Rep: 512
    Location: New York

    missinginaction Senior Member

    A 140 degree thermostat is consistent with a raw water cooled engine. You have a restriction somewhere in the system. Probably in the riser(s) and or manifolds due to age and corrosion. You should be able to put your hand on the riser when the engine is running without burning yourself. If the risers or the rubber bellows below the risers are very hot you have a restriction. Good luck and welcome to the forum.
     
  4. IMP-ish
    Joined: Jan 2011
    Posts: 389
    Likes: 9, Points: 18, Legacy Rep: 150
    Location: united states of america

    IMP-ish powerboater

    Did you change both drive pump and engine circulating pump?
     
  5. gonzo
    Joined: Aug 2002
    Posts: 13,413
    Likes: 333, Points: 93, Legacy Rep: 2031
    Location: Milwaukee, WI

    gonzo Senior Member

    Before changing parts and spending time on it, you should troubleshoot the engine first. How are you measuring the temperature, and at what location in the engine?
     

  6. Ike
    Joined: Apr 2006
    Posts: 2,214
    Likes: 170, Points: 63, Legacy Rep: 1669
    Location: Washington

    Ike Senior Member

    I would agree that you have a restriction somewhere, and I would suspect the exhaust manifold. My 72 Sea Ray has a 165, but for a while I had a similar problem. It had all new hoses, and a new waterpump, but still ran hot. Mine is raw water cooled. When I pulled the manifold it was corroded to the point of blocking the cooling water. A new manifold cured it. On the outside the manifold looked fairly new but inside, oh my!
     
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