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    Temp Sender / Gauge Questions:


    Hi Guys,


    Engine not overheating.

    Alarm is going off.

    Oil in Lower Unit good.

    Oil in Engine good - pressure- 40 - 45 - psi.

    ==========================================


    Where does the Alarm get its signal from if there's an overheating issue? From the Alarm Sensor itself or from the Temp Sender or Temp Gauge if a short is present?

    if there's a Bad Temp Sender or Bad Temp Gauge or a Short somewhere in between the two, can that trigger the Aarm?

    Also I think I found the Temp Sender but where's the Alarm Sensor?

    Going to try to get down to the boat tonight to do some testing.

    Engine: 7.4 - MPI

    YR. 2000 CIERRA SUNBRIDGE


    Thanks
    Ed

    #2
    The helm temp gauge gets its reading from a temp sender which is a resistor that varies resistance with temp. The alarm uses a separate sender witch is a switch that is open until it’s threshold is met then closes and the alarm sounds. Typically both of the senders are on the thermostat housing on opposite sides.

    have you taken measurements with an IR temp sender? This will give you an independent reading and let you know if the helm gauge is correct or not as well as if the alarm is going off prematurely. Then you’ll know what needs to be investigated.
    1997 Maxum 2400 SCR 5.7LX Bravo II

    Mike

    Comment


    • builderdude
      builderdude commented
      Editing a comment
      Agree to check temps with an IR gun.
      According to OP’s other thread the gauge was also acting strange.

    #3
    Mike, does Merc do something similar to what Volvo Penta has done by incorporating high temp switches in the exhaust elbows?
    Just a thought!
    Rick E. Gresham, Oregon
    2850 Bounty Sedan Flybridge model
    Twin 280 HP 5.7's w/ Closed Cooling
    Volvo Penta DuoProp Drives
    Kohler 4 CZ Gen Set

    Comment


      #4
      Originally posted by 2850Bounty View Post
      Mike, does Merc do something similar to what Volvo Penta has done by incorporating high temp switches in the exhaust elbows?
      Just a thought!
      Rick to be honest I don’t know but if they did in would be a much newer boat than the OP, most likely once they required converters in the exhaust.
      1997 Maxum 2400 SCR 5.7LX Bravo II

      Mike

      Comment


        #5
        Mike...... good point.
        I do know that for certain that Volvo Penta used this in some 2003 models.
        Rick E. Gresham, Oregon
        2850 Bounty Sedan Flybridge model
        Twin 280 HP 5.7's w/ Closed Cooling
        Volvo Penta DuoProp Drives
        Kohler 4 CZ Gen Set

        Comment


          #6
          As Mike said: a separate switch triggers the alarm when it’s set temperature is reached.

          Mike, is the temp switch in the t stat housing or the intake manifolds water jacket?

          Eddie, from your other thread: Are you still seeing strange behavior from the temp gauge also? May have two separate issues.
          Dave
          Edmonds, WA
          "THE FIX"
          '93 2556 5.7 Bravo II 2.0:1 18 1/4x19 P
          (.030 over-Vortec top end-part closed cooled)
          The rebuild of my 2556 https://www.baylinerownersclub.org/f...76?view=thread
          Misc. projects thread
          https://www.baylinerownersclub.org/f...56-gctid789773

          Comment


          • Nauti_Mike
            Nauti_Mike commented
            Editing a comment
            The ones I have seen are in the thermostat housing opposite side from the gauge sender

          #7
          Hi Guys,

          I am going down to the boat with the IR Gun later on. As for the Temp gauge, it always runs around 125 to 130 deg. after warmed up for the last 10 years. Never overheated. The last time out, the Gauge worked fine then the next time I went out about a week later the Gauge was around 120 then dropped to 100 and within 10-20 seconds the needle bounce up to 110 then dropped again to 100 then up to 110 then dropped slightly below the 100 mark which is the lowest the needle can go and never moved since. \

          At canal speed or up to 7-8 MPH in the bay there is NO ALARM. As soon as I get up on plane the ALARM SOUNDS within 1-2 mins. Back to canal speed or a bit faster the ALARM STOPS. If I go back on plane it repeats. This routine repeats itself over and over, but it does not overheat.


          Ed

          Comment


            #8
            First the helm gauge is not acting correctly; bad thermostat, sender, gauge, wiring. Since the alarm sounds at higher rpm the impeller may be bad or there is a restriction
            1997 Maxum 2400 SCR 5.7LX Bravo II

            Mike

            Comment


            #9

            As mike alluded to: the temp switch (assuming it’s functioning correctly) is triggering the alarm at higher rpm, that’s usually an indication of poor cooling water flow, likely a worn or failing impeller. Verification with the IR gun will tell you what the actual temp is.
            Dave
            Edmonds, WA
            "THE FIX"
            '93 2556 5.7 Bravo II 2.0:1 18 1/4x19 P
            (.030 over-Vortec top end-part closed cooled)
            The rebuild of my 2556 https://www.baylinerownersclub.org/f...76?view=thread
            Misc. projects thread
            https://www.baylinerownersclub.org/f...56-gctid789773

            Comment


              #10
              OK Guys,

              Thanks … Going down in an hour. I will post the Temps later on tonight. I will make a prediction that the Temp of the motor is OK, but we'll see.

              Ed

              Comment


                #11
                Keep in mind that the oil pressure sender for the gauge and the oil pressure switch for the alarm are usually different units. Your boat may have a bad oil pressure switch.
                1999 3788, Cummins 270 "Freedom"
                2013 Boston Whaler 130 SS
                Anacortes, WA

                Comment


                • builderdude
                  builderdude commented
                  Editing a comment
                  We be talkin bout temps Willis 🤪

                • Nauti_Mike
                  Nauti_Mike commented
                  Editing a comment
                  Lol Dave

                #12
                My motor started life as a 2003 merc. 2 senders on the thermostat housing. Nothing on the exhaust system
                1992 2452
                5.0 alpha1 gen2

                Comment


                  #13
                  Hi Guys,

                  I got the results with the IR Temp Gun:

                  7.4MPI 2000yr. Ciera Sunbridge / Bravo III Dual Props.


                  After 25 minutes of running at 1200 to 1800 RPM bringing the throttle up and down for about a minute at each RPM range.

                  I have had the boat for 10 years and it has always run around 125 to 130 deg.

                  Starboard Riser - 106 deg.
                  Port Riser - 96 deg.
                  Manifold - 116 deg.
                  Thermostat Cover - 122 deg.
                  The cover where the four hoses connect. in front of the thermostat - 109 deg.
                  On The Temp Sender unit. - 126 deg.




                  The Temp Sender is on the Starboard side of the Thermostat housing. Exactly opposite on the other side where I thought I would find the Alarm Switch, I found a Brass Plug. Not sure where the Alarm Switch is.

                  The Sender also has a Dark Brown or Black wire with a Tan Stripe. The Schematic shows Tan. I don't know why, maybe they changed the color code on it midstream.

                  I checked the Temp Gauge itself. I ground the Dark Brown or Black wire with a Tan Stripe. Then turned "ON" the Ignition and the Temp Gauge went all the way over to 250. Turned "OFF" and the Needle dropped right back down to 100. I think the Gauge is OK.

                  I took an Ohm Meter to the Sender and I checked between the tip of the Sender and Ground and set the Meter to 20K, and got very erratic numbers. Ex. 1.0, 1.786, 0.00. Also this Sender has about 3/4" of threads on it that a right angle boot at the end of the Dark Brown or Black wire with a Tan Stripe wire connects to it. I guess it's time to replace the Sender unit.


                  Question: If I remove the Sender will I get a flood of water coming out or just a little bit. I just want to know what to expect.

                  Any suggestions or comments ??

                  Thanks Again

                  Eddie



                  Comment


                    #14
                    You need to check temps at cruise speed up on plane, that’s where your alarm was being triggered. The sender for the gauge could be malfunctioning but also look at the sender wire at the senders end, corrosion can find its way into the wire near the end.
                    Dave
                    Edmonds, WA
                    "THE FIX"
                    '93 2556 5.7 Bravo II 2.0:1 18 1/4x19 P
                    (.030 over-Vortec top end-part closed cooled)
                    The rebuild of my 2556 https://www.baylinerownersclub.org/f...76?view=thread
                    Misc. projects thread
                    https://www.baylinerownersclub.org/f...56-gctid789773

                    Comment


                      #15
                      Originally posted by Norton_Rider View Post
                      Keep in mind that the oil pressure sender for the gauge and the oil pressure switch for the alarm are usually different units. Your boat may have a bad oil pressure switch.


                      builderdude commented

                      We be talkin bout temps Willis 🤪
                      --------------------------------------------------------------------------------------------------------------------



                      Not necessarily, the OP stated in the first post:

                      "Engine not overheating.

                      Alarm is going off.

                      Oil in Lower Unit good.

                      Oil in Engine good - pressure- 40 - 45 - psi."



                      It shouldn't be assumed that it is a temperature issue, since the most common reason for alarms going off is a bad oil pressure switch. Since the switch and the pressure sender are independent, having good oil pressure does not eliminate the pressure switch as a culprit.
                      1999 3788, Cummins 270 "Freedom"
                      2013 Boston Whaler 130 SS
                      Anacortes, WA

                      Comment

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