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  • Temperature sensors

    Originally posted by Juniorcarp View Post
    Re: Normal operating temp merc 305 5.0

    Had the impeller done this spring and changed the circulating pump also changed the two sensors at the thermostat housing !
    Are those two sensors the same? I'm assuming they are both temp switches, but I'm not 100% sure. Thanks.

  • #2
    Originally posted by smilex100pre View Post

    Are those two sensors the same? I'm assuming they are both temp switches, but I'm not 100% sure. Thanks.
    You should open up your own thread instead of posting on a 7 year old one.

    One is a sensor for the gauge and the other is a switch for the alarm.
    83 Sunrunner 16.5 120 merc Alpha 1 drive SOLD 8/1/13

    1996 Crownline 202BR
    5.7l EFI 0f791070
    Bravo I drive

    GMC Yukon tow rig

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    • #3
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      Hello smilex100pre and aboard...

      I have created a new thread for you, but generally, once a thread is 90 days old, unless you are the original poster, we request they be left alone as our archive...

      On to your question...To know exactly what sensors are there we need a bit more information about the engine. Carburetored engines had just a gauge sender (variable resistor). Then the alarm system was added in the 90's and that added a temperature switch, which grounded the alarm line and allowed the buzzer to sound if the engine got too hot...

      With the advent of injected engines, the alarm switching function was handed off to the ECU, and the second sensor was a digital sender for the ECU...

      Hence, when you post a request for help, we ask for the following....

      Engine model, year and serial number.

      Based on those we may ask for more information, like if it's an early injected engine, we may ask if it's MEFI1 or MEFI3 (And we generally post a picture of the 2 units so you can see the differences), or if you're asking about an alternator, we'll ask which one (Merc used about 4 different alternators at various stages).... If it's a cooling question, include if the engine is raw or close cooled.

      Have a read through the 'stickies' and get acquainted with the information available in there too...

      Stickies. -> https://forums.iboats.com/forum/engi...rch-version-of

      Chris..........
      iboats Mod team
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      The world takes on a whole new perspective when viewed from 100’ below.
      1972 Bertram ‘Bahia Mar’ 20
      2006 Mercruiser 4.3MPI (0W617679) w/Alpha One Gen II (0W829301)
      (Original - 1972 '165' In-line 6. Previous - 1994 4.3LX)


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