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  1. #1
    Mike Florence's Avatar
    Mike Florence Guest

    Default " I have a 2000 model 150 Salt

    " I have a 2000 model 150 Saltwater mercury outboard that sets off the high temp alarm at random intervals. Once the alarm sounds, engine off and restart, I may go 20 miles without another alarm. Took to dealer and they replaced t'stats and said this should do it. First run out within 2 miles of launch point, alarm goes off again. Trolled afterwards for 4 hours (no problem). The water stream from the pee hole is strong and no water inlet blockage. Have flushed engine and even removed hoses and run to check for blockage. Dealer said water pump should be ok and water temp test at 1500 rpm was 150 degrees. Any suggestions? "

  2. #2
    Join Date
    May 2001

    Default "Mike, Does the alarm sound


    Does the alarm sound a single long beep, or a series of short beeps?


  3. #3
    Mike Florence's Avatar
    Mike Florence Guest

    Default One long sound. It's not

    One long sound. It's not the oil alarm.

  4. #4
    Join Date
    May 2001

    Default "Mike, Just checking, so we


    Just checking, so we don't head in the wrong direction.

    I would suspect the heat sensor. Generally you have two of them; one is for a temp gauge and the other is for the alarm. They are located on the cylinder heads.

    Determine which sensor activates the alarm, by disconnecting the wire and touching it to ground with the key in the "on" position. If the alarm goes off you have the sensor that you are looking for.

    You have to determine whether the alarm is being set off by the sensor or some other problem, such as a short somewhere in the circuit. It may take some time and patience to do this.

    The easiest way to proceed is to run the engine until the alarm sounds, and then disconnect the sensor. If the alarm stops beeping, then you know the sensor is causing it to go off. If it continues to sound, you have a problem somewhere in the circuit. If the sensor is triggering the alarm you might as well just replace it and see if the problem clears up. If you want you can remove it and test it to determine at what temperature it is grounding the circuit at. If you have a temperature probe you can do this with the sensor in place. If not, then you have to heat it in a water bath while monitoring the continuity between the wire and the body of the sensor, and the temperature of the water.

    The difficulty that you will probably run into is that the problem is intermittent, which means that it probably will not happen when you want it to. You might also try touching the head near the sensor while the engine is running to determine if that one location is heating up more than the rest of the engine. Of course you have to be very careful if you try this. A temperature probe would be very useful here also.


  5. #5
    Mike Florence's Avatar
    Mike Florence Guest

    Default Thanks Tony. Will try your su

    Thanks Tony. Will try your suggestions. Just a word; went offshore today and run a total of 60 miles at different speeds. Alarm never went off. I agree with you in that there may be a short or faulty sensor. Thanks again!

  6. #6
    Jim Franklin's Avatar
    Jim Franklin Guest

    Default " This is some very good infor

    " This is some very good information. I have been plagued by this problem for months with a 2000 EFI 200 that overheats and I cant seem to nail down the problem,and it overheats within 2 miles. I have changed the head gaskets,Thermostats, Cut the centers out of the old ones just to see what that would do ,New waterpump, New gaskets in the center section,complete popoff valve replacement,timing is righton,Lowered the motor 2 inches, removed water manifold and ran steel cable thru every conceivable hole in the motor checking for obstuctions,Backflushed everything,ad now that I read about the sensors and with all i have found wrong with the rebuild that i had done by a very good recomended mechanic , could it be he installed the wrong sensors or both have gone bad at the same time. They never work the same was twice.And now I remember changing to all new guages just before this all took place and to me the motor has never seemed to be all that hot. I have had 4 mechanics try to figure this out and they throw their hands up and say they dont know what to do rather to disassemble the engine and start over. Is ther anything else that could be the problem. "

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