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Engine Alarm - Possible Causes?

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    Engine Alarm - Possible Causes?

    Yesterday I started the engines (Cummins 6BTA, 270 HP engines) in my boat and headed out of the marina. After less than 5 minutes of operation at idle RPM the port engine alarm went off. Voltage, and Oil Pressure at both helms were normal. The water temperature on both engines was quite low, but I was at less than 1000 RPMs, waiting for the temps to come up. I checked the exhaust and it appeared to have the proper amount of water coming out. I shutdown the engine and restarted it to see if that cleared the issue; it did not so I shut it down again and returned to my slip.

    Now the issue is where to start troubleshooting. I'm not at the boat, so I don't have the Cummins service and repair manual with me. To my knowledge the alarm is wired to the oil pressure switch, water jacket temperature switch, and exhaust thermocouple switch. Is it also wired to an alternator voltage sensor?

    Two things have been replaced in the last couple of months:

    1- Raw water pump impeller. If the impeller went TU this would affect the water flow, overheating could occur and trigger the thermocouple switch. But the water flow that I observed appeared to be normal. Also, the alarm went off after less than 5 minutes at idle. It doesn't seem like the temp would climb that quickly.

    2- Oil pressure sender (gauge sender, not the alarm switch). I did not replace the sender myself. It was done by my mechanic. The space between the port side of the engine and the fuel tank is really tight. I wonder if the mechanic unknowingly snagged and pulled the pressure switch wire off. The thing is that most oil pressure switches are normally closed and they open when oil pressure is sensed. Disconnecting a wire will just open the circuit.

    Any ideas?
    1999 3788, Cummins 270 "Freedom"
    2013 Boston Whaler 130 SS
    Anacortes, WA

    #2
    Raul, maybe your 270 is different to my 370. I'm unaware of any exhaust thermocouple sensor. On the gennie, yep, but my understanding there is an oil pressure switch, a coolant switch, and alternator/electrical switch in the alarm loop. You're right in that they are normally closed. One of my alarms goes off when the revs drop at low idle and a bit more throttle fixes that. The switches are different to the senders and are close to each other on my 370. If your mechanic pulled it off, then it wouldn't have kicked in after 5 mins, would have been immediate when you started the engine, the alarm wouldn't have gone off. If your raw water flow and other pressure/temp/volts are ok, its potentially one of the two switches, coolant or oil pressure.

    I can't remember whether there were two wires to the oil and coolant switches or one, but you need to bridge them shut to test one at a time. If they are two wires, last time on my gennie coolant switch, I bridged the circuit with a paper clip. If it's one wire, bridge it to earth. Short of buying new replacement switches, which aren't bad spares to have, I'd try to troubleshoot first. The engine of course has to be running say 800-900 revs. Certainly hard to get to on the port engine. I think you'll need a helper.

    Have fun! Cheers
    John H
    Brisbane QLD Aust
    "Harbor-nating"

    2000 - 4788/Cummins 370's

    Comment


      #3
      I would start with the oil pressure switch (not pressure sending unit). Mine failed and alarm would sound even though I had good pressure. Was an easy fix. You could try swapping between engines to test.

      Comment


        #4
        Originally posted by higgins_jr View Post
        Raul, maybe your 270 is different to my 370. I'm unaware of any exhaust thermocouple sensor. On the gennie, yep, but my understanding there is an oil pressure switch, a coolant switch, and alternator/electrical switch in the alarm loop. You're right in that they are normally closed. One of my alarms goes off when the revs drop at low idle and a bit more throttle fixes that. The switches are different to the senders and are close to each other on my 370. If your mechanic pulled it off, then it wouldn't have kicked in after 5 mins, would have been immediate when you started the engine, the alarm wouldn't have gone off. If your raw water flow and other pressure/temp/volts are ok, its potentially one of the two switches, coolant or oil pressure.

        I can't remember whether there were two wires to the oil and coolant switches or one, but you need to bridge them shut to test one at a time. If they are two wires, last time on my gennie coolant switch, I bridged the circuit with a paper clip. If it's one wire, bridge it to earth. Short of buying new replacement switches, which aren't bad spares to have, I'd try to troubleshoot first. The engine of course has to be running say 800-900 revs. Certainly hard to get to on the port engine. I think you'll need a helper.

        Have fun! Cheers
        Thanks for the comments. My engine has a thermocouple attached to the exhaust risers. I assume it is connected to the alarm system because I the only temperature gauges on my boat are for engine coolant.

        Before I shut the engine down I tried revving it up a bit to see if the alarm would stop. But that had no effect.

        I may call the mechanic on this one due to the pressure switch location. BTW, my mechanic is in business with his 20-some year old son. Guess which one of the two gets to... go into tight spaces, such as the port side of the port engine, haul 8D batteries, etc?.....
        1999 3788, Cummins 270 "Freedom"
        2013 Boston Whaler 130 SS
        Anacortes, WA

        Comment


          #5
          Originally posted by Average_Joe View Post
          I would start with the oil pressure switch (not pressure sending unit). Mine failed and alarm would sound even though I had good pressure. Was an easy fix. You could try swapping between engines to test.
          Thanks, sounds like a good idea.
          1999 3788, Cummins 270 "Freedom"
          2013 Boston Whaler 130 SS
          Anacortes, WA

          Comment


            #6
            On my Cummins the alarm sounded when the over temp alarm switch failed. Mine is located on the top forward end of the engine, single wire into it.

            Comment


              #7
              If the alarm is on all the time then just removing the wire is going to provide the test if it stops. No need to swap the sensors.
              Future 4788 Owner
              Charleston, S.C.

              Comment


                #8
                Hi there, Norton Rider. I remember those 850 Featherbed Nortons from when being in the army at Fayatville in 1967. The dealer, Meridiam Motorcycle, used to sell them with special paint jobs on the tank. Our 325 eats up engine overheat alarms at such a rate that I have disconnected them and rely on the gauge. My opinion is that the quality of those censers is below par. I have changed at least a half dozen of them and when they fail I get an intermittent alarm on plane or rough water. Everything else checks out fine. Best of luck with your annoying alarm! Griff

                Comment


                  #9
                  I'll try to go to the boat today and disconnect the sensors that I can reach one by one and start the engine each time.
                  1999 3788, Cummins 270 "Freedom"
                  2013 Boston Whaler 130 SS
                  Anacortes, WA

                  Comment


                    #10
                    Originally posted by bruce griffith View Post
                    Hi there, Norton Rider. I remember those 850 Featherbed Nortons from when being in the army at Fayatville in 1967. The dealer, Meridiam Motorcycle, used to sell them with special paint jobs on the tank. Our 325 eats up engine overheat alarms at such a rate that I have disconnected them and rely on the gauge. My opinion is that the quality of those censers is below par. I have changed at least a half dozen of them and when they fail I get an intermittent alarm on plane or rough water. Everything else checks out fine. Best of luck with your annoying alarm! Griff
                    I've owned my 74 Norton Commando for almost 40 years. I like it so much that I've bought and sold about 60 motorcycles in that time period, but I never had the urge to get rid of the Norton.
                    1999 3788, Cummins 270 "Freedom"
                    2013 Boston Whaler 130 SS
                    Anacortes, WA

                    Comment


                      #11
                      Problem solved.... I did not have time to go by the boat today, but the mechanic had another job at the marina and took a look at my boat. The exhaust over-temp switch had a terminal bent over and it was shorting out. He straightened the contact and that solved the problem.

                      The switch on my boat looks a bit like these: https://encrypted-tbn0.gstatic.com/i...skgJS1vE36ZFny
                      1999 3788, Cummins 270 "Freedom"
                      2013 Boston Whaler 130 SS
                      Anacortes, WA

                      Comment


                        #12
                        That mechanic is a keeper.
                        Guntar
                        1999 3988
                        Cummins 270s

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