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Open cooling system temp question

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  • Open cooling system temp question

    1984 Seaswirl Sierra OMC 3.8L

    Owners manual indicates engine temp should be between 150 & 170 degrees. Does that mean at all times like in a car where once the engine is warm the themostat keeps the water temp at whatever setting the thermostat is? Reason I ask is today I noticed my water temp gauge indicating around 120 for mid range cruising and during WOT it climbed to 140. In July on our very first trip out I remember seeing 180 at WOT and I think around 160 at lower rpm.
    Wondering if my thermostat is stuck open or if gauge/sender is going bad.

  • #2
    you probably have a broken or stuck thermostat or a bad gauge sender.

    use an infared thermometer to diagnose, replace as required.
    1988 Cruisers Rogue 2420 -VP 290 DP now powered by custom 468 - http://forums.iboats.com/forum/owner...988-rogue-2420

    Past Boats
    1970 Wooster Hellion - Merc 9.8
    2002 SeaRay 190BR - 5.0 - A1G2 - "Cheasheads in Paradise"
    1984 Avanti 170DLI -3.0 stringer- "Ship Happens"

    What’s behind you doesn’t matter.Enzo Ferrari

    Comment


    • #3
      Ayuh,.... If ya haven't replaced the impeller in the raw water pump,....

      I'd start there,....

      Comment


      • #4
        The lower than normal temps could be as simple as a piece of rust holding the thermostat open a bit. Happens a lot in raw water cooled engines. Might need a bit of cooling system maintenance as noted above.
        1988 Four Winns 200 Horizon
        4.3 OMC Cobra

        98 Jeep Grand Cherokee 4.0 Selectrac
        07 Jeep Grand Cherokee Limited 5.7 Quadradrive II

        "While air doesn't freeze....rust never sleeps"

        Comment


        • #5
          Thanks fellow boaters!
          The thermostat was stuck open about an 1/8" Nothing holding it open that I could see but it needed to be changed. The o-ring was rock hard and I wonder if it wasn't the original thermostat.
          Now the amazing part of the story. I live in a rural area and we have a small marine shop just outside of town. From the road the shop looks like a place you wouldn't want to stop and most of the boats parked there are old & tired. I would have never gone their except a friend of mine who has 10 boats told me the shop was really good. I took my old thermostat & o-ring with me and asked if they had a new one. Doggoned if they didn't have the kit in stock and it was cheaper than buying on line & paying shipping.
          I installed the new parts and fired her up on the muffs. Temp gauge climbed to 180 and stayed there and once warmed up the engine idled smoother and quieter. AWESOME!!!!!
          Used my infrared thermometer and couldn't find a temp over 154 anywhere in the cooling system. Think the stock temp gauge reads high.

          Comment


          • #6
            Normal OMC thermostats are a 160* unit. The normal temps I have seen are 160-175. I also check temps with an IR temp gun. I have found that the area on the engine that seems to follow the dash gauge most accurately is the part of the intake manifold that is right under the thermo housing. When my dash gauge says 160*, this area reads 145-155 or so. If you stock gauge is in fact reading high check all the connections for the temp gauge (sending unit on the engine, terminals on the temp gauge) for corrosion and excessive resistance.
            1988 Four Winns 200 Horizon
            4.3 OMC Cobra

            98 Jeep Grand Cherokee 4.0 Selectrac
            07 Jeep Grand Cherokee Limited 5.7 Quadradrive II

            "While air doesn't freeze....rust never sleeps"

            Comment


            • #7
              Now pull the drive apart and replace the raw water pump
              1988 Cruisers Rogue 2420 -VP 290 DP now powered by custom 468 - http://forums.iboats.com/forum/owner...988-rogue-2420

              Past Boats
              1970 Wooster Hellion - Merc 9.8
              2002 SeaRay 190BR - 5.0 - A1G2 - "Cheasheads in Paradise"
              1984 Avanti 170DLI -3.0 stringer- "Ship Happens"

              What’s behind you doesn’t matter.Enzo Ferrari

              Comment


              • #8
                Originally posted by Lou C View Post
                Normal OMC thermostats are a 160* unit. The normal temps I have seen are 160-175. I also check temps with an IR temp gun. I have found that the area on the engine that seems to follow the dash gauge most accurately is the part of the intake manifold that is right under the thermo housing. When my dash gauge says 160*, this area reads 145-155 or so. If you stock gauge is in fact reading high check all the connections for the temp gauge (sending unit on the engine, terminals on the temp gauge) for corrosion and excessive resistance.
                Although the connection didnít look damaged or corroded, I cleaned the terminal on the sender before deciding to pull the thermostat housing. The gauge would indicate lower than actual temp if there was excessive resistance.
                Iím ok with the 34 year old gauge being a bit off. 🙂 kinda like the owner

                Comment


                • #9
                  Originally posted by Scott Danforth View Post
                  Now pull the drive apart and replace the raw water pump
                  It was replaced in July

                  Comment


                  • #10
                    Sign up today
                    After changing the thermostat I gave the boat a bath and went to lake Pend Oreille. Family was away so this was my first solo trip.
                    Yesterday cruising though the no wake zone of Buttonhook Bay the temp gauge stayed at 100, today, 180 indicated which should be 160ish. Boat runs so much better now.

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