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Force 150 Outboard overheat warning-gctid811836

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    Force 150 Outboard overheat warning-gctid811836


    I am wondering if any of you Force outboard owners have any thoughts on the overheat warning sensor

    I have a 1994 Force 150 that I've owned since it was new. I use it several times a year and always have it serviced. I've never had any problems with this engine until the last time it was serviced.

    It was getting water in the gear case, so the dealer replaced the seals and while they were at it, replaced the impeller. They also REMOVED the thermostat--with a note on the receipt that the thermostat is not necessary unless in cold water (not sure I agree with this, but I went along with it since it was a mercury/Force service shop)..

    I've only used the boat three times since this repair, and I've found that it works fine...I can cruise and pull a tube around all day, but then if I decide to slowdown fior a ride at or around idle speed, the overheat warning goes off.

    I immediately shut it down and remove the cowl to air cool so I can start it again. Then after waiting about 10 mins, I can start and run again at full high speed with no issues.

    3 questions

    1. Is it legit to run without a thermostat, and could this actually be causing the overheat at idle? I plan to replace it myself ( the problem seems too much of a coincidence to ignore) but wondering if the repair shop doesn't know what they are talking about.

    2. Other than replacing the impeller and checking for blockages is there anything else I should check or replace to troubleshoot overheat at idle?

    3. Does anyone know at what temperature the overheat warning goes off vs. what temperature you actually do engine damage? I'm hoping by shutting down immediately when that sensor went off that I'm going to be ok. I'd hate to think that the warning sensor is more like a "oops you are too late..." sensor. I can't find anything around this online.

    The overheat sensor has gone off exactly three times. The first two I thought were due to seaweed clogging intake. But now thinking its impeller. I always immediately decelerated and powered hoping I didn't cause any damage... it's been a good motor for a lot of years (even though I hear a lot of gripes about the Force brand--this ones not caused me any headaches).

    Any help would be appreciated!

    Not sure if anyone else is following this thread other than me , but I posted on another forum online, and got some helpful information, and I'll post it to help other bayliner owners. I was told that potentially the thermostat is ensuring the block completely fills up to maximize the value of the cool lake water. Without a thermostat, the water is quickly going in and out, and not really being forced into "all corners" of the engine that need to be cooled.

    I'm going to replace the thermostat and see if that alone fixes the overheat problem before dropping the lower unit to replace the impeller. FYI, I'm also told that 130 is normal operating temperature. The overheat warning goes off around 150-160, which is lower than a damaging temperature--so if you shut down right away, it shouldn't be a big deal.

    I'll post my results after installing the thermostat.


      Update: Installing the thermostat completely fixed this overheat at idle problem. So for any other FORCE 150 owners out there--don't let someone tell you that the thermostat isn't necessary in warm water environment. It most definitely is!


        And the impeller looked like what ?

        The old t-stat was rusted closed ?

        You tried running without the t-stat ? You still had the warning, funny if you have a gauge at the helm that gauge should not have moved, or moved a fraction, see the sensor would only be reading cool water.

        That engine have pop-it valves ? This question is the one i really want a reply to.
        Be good, be happy, for tomorrow is promised to no man !

        1994 2452, 5.0l, Alpha gen. 2 drive. Sold ! Sold ! Sold !

        '86 / 19' Citation cuddy, Merc. 3.0L / 140 hp 86' , stringer drive. Sold ! Sold ! Sold !

        Manalapan N.J


          A mechanic removed my thermostat as a "preventative." He said if the thermostat stuck closed, it would cause an overheat. And said since I was using the boat in summer in warm water, the thermostat would always be open anyway, so it wasn't needed. However...ever since he did that, I had overheat problem

          The impeller is new

          This engine does not have a poppet valve.

          Seems only the thermostat alone fixed this issue. It must serve some purpose of keeping water in the system addition to its primary purpose.


            A quick one ...

            Brother buy's a new rig 76 or 74 it's been a couple of years maybe i have some old paper work for the outboard and boat.

            Anyway i'm visiting him in Texas rig was maybe 3-5 years old, and the outboard overheats on the water.

            We allow the engine to cool down, i remove the t-stat and we continued fishing, and that engine never had another one installed.

            I know cause i towed up that rig to Jersey and had it for another 20 years or more used 2 weeks every year, on a fresh water lake upstate ny near my summer home.

            That boat never kissed saltwater, from manufacture till i sold it about 10 years ago.
            Be good, be happy, for tomorrow is promised to no man !

            1994 2452, 5.0l, Alpha gen. 2 drive. Sold ! Sold ! Sold !

            '86 / 19' Citation cuddy, Merc. 3.0L / 140 hp 86' , stringer drive. Sold ! Sold ! Sold !

            Manalapan N.J


              Interesting! It seems some outboards must do just fine without a thermostat. Yours did! Makes sense since the mechanic clearly wasn't trying to cause any harm to me...he must have removed them a lot of times with fine results...

              Unfortunately my Force 150 didn't like not having one in there!


                Here is a flow diagram from a different motor, but they all work the same.

                Here you can see that in cold water, the Tstat is not as important in cooling since the water is very cold and more flow going faster. Although even in cold water, the Tstat allows the engine to heat up to desired operating temps.

                Now when you run slow, if Tstat is removed, there is now a constant flow thru the engine and out, and this is when the water is not removing much of the heat because it's just running thru so fast it doesn't have time to absorb and remove heat.

                The Tstat is just a regulating valve opening/closing based on heat instead of pressure.

                Take for instance a water radiator heater used up north. Hot water is not just flowing in and out of the heater as fast as possible, rather it fills the radiator, allows heat to be radiated into the room, then flows out and get's heated back up and sent thru the system again etc.