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  1. #1
    Join Date
    Dec 2006
    Location
    Lake St Clair /Detroit, MI, USA
    Posts
    335

    Default Question..Are both the temp ga

    Question..Are both the temp gauge and temp alarm senders the same in construction and function????
    One will jump a touch to show power on the water gauge when the ignition is on but will not read any temp as the engine warms up. If I switch the temp gauge wire to the other it will not show any reaction to power at all when the ignition is on and will not show any temp readings as the engine warms up.

  2. #2
    Join Date
    Aug 2006
    Location
    SW Ohio, USA
    Posts
    10,396

    Default No; the gauge uses a thermisto

    No; the gauge uses a thermistor that reacts slowly to temp. changes continuously. The alarm uses a normally open thermal switch set to close at a specific temperature to trigger the alarm.

    To test the gauge just ground the sending wire and it should peg the gauge needle. To test the sender remove the sender wire and connect an ohmmeter positive lead to the center tab and the black neg. lead to the case. Set the meter on the 500 ohm scale. Apply heat to the copper end of the sender and watch the change in ohms.

    Your T'stat probably is open all the time or missing altogether.
    Fix minor things (replace wear items for preventative maintenance.) that cause major problems before they break.

  3. #3
    Join Date
    Dec 2006
    Location
    Lake St Clair /Detroit, MI, USA
    Posts
    335

    Default Ok so I checked everything. Fi

    Ok so I checked everything. First I put in a new rubber water pump rotor so I'm getting lots of fresh water. I put in a new 160 d mercruiser T'stat and a new mercruiser temp sender part number 306490T and it indicates power when the ignition is on. When I did the ground test on the gauge it did peg full. but...when I run the engine for about 15 minutes at idle the guage never moves up. The engine does seem to be running cool. If I touch the T stat housing it is not ver warn to the touch at all. What up with that? Anyone know if this is the right water sender part number for the gauge?

  4. #4
    Join Date
    Dec 2006
    Location
    Lake St Clair /Detroit, MI, USA
    Posts
    335

    Default "turns out that sender number

    "turns out that sender number is 806490T and looks like the right sender, the sierra equivalent is 18-5897"

  5. #5
    Join Date
    Aug 2006
    Location
    SW Ohio, USA
    Posts
    10,396

    Default What engine and year is this o

    What engine and year is this one?

    The thermostat goes in w/the copper pellet down. Did you put anything on the temp. sender threads? Nothing on the threads.
    Fix minor things (replace wear items for preventative maintenance.) that cause major problems before they break.

  6. #6
    Join Date
    Dec 2006
    Location
    Lake St Clair /Detroit, MI, USA
    Posts
    335

    Default "This is a 454. The block is a

    "This is a 454. The block is a newer roller short block..2002 or 2003 but the intake is from a 1993 mag engine. It has the large thermostat cover with 4 hoses going into it. The thermostat is in pellet side down into the block, the sender gauge has only the coating on the threads it came with. The weather has been crappy so I have actaully had the boat out on the lake at speed yet."

  7. #7
    Join Date
    Aug 2006
    Location
    SW Ohio, USA
    Posts
    10,396

    Default Check the wires on the back of

    Check the wires on the back of the gauge. Corrosion may be keeping the needle from moving w/a small amount of voltage. Also pull the main engine "barrell plug" apart and check for corrosion.
    Fix minor things (replace wear items for preventative maintenance.) that cause major problems before they break.

  8. #8
    Join Date
    Dec 2006
    Location
    Lake St Clair /Detroit, MI, USA
    Posts
    335

    Default I already pulled the gauge and

    I already pulled the gauge and checked the connections. What is the main engine "barrell plug"?? Where do I find it?

  9. #9
    Join Date
    Aug 2006
    Location
    SW Ohio, USA
    Posts
    10,396

    Default On top of the engine where the

    On top of the engine where the main electrical connection is made between the engine and the boat wiring. Usually on the starboard exhaust elbow.
    Fix minor things (replace wear items for preventative maintenance.) that cause major problems before they break.

  10. #10
    Join Date
    Dec 2006
    Location
    Lake St Clair /Detroit, MI, USA
    Posts
    335

    Default "Interesting, Are these only f

    "Interesting, Are these only found on marine engines? Are they mounted internally or externally ? Between what and what? What do they look like? My engine does not have the standard exhaust water jackets/manifolds it has been retrofitted recently with high performance high rise direct exhaust manifolds. Is there somewhere I could find a picture?"

  11. #11
    Join Date
    Aug 2006
    Location
    SW Ohio, USA
    Posts
    10,396

    Default "It may be mounted on the star

    "It may be mounted on the starboard front next to the 50 amp main breaker.

    http://www.mercruiserparts.com/Show_...+TB+IV"
    Fix minor things (replace wear items for preventative maintenance.) that cause major problems before they break.

  12. #12
    Join Date
    Dec 2006
    Location
    Lake St Clair /Detroit, MI, USA
    Posts
    335

    Default Ok I know where the 50 amp bre

    Ok I know where the 50 amp breaked and solenoid are but am I missing something in the picture of the wiring harness attached? Which componet is the barrel value?

  13. #13
    Join Date
    Aug 2006
    Location
    SW Ohio, USA
    Posts
    10,396

    Default #1 fits into #2 & #4 mount

    #1 fits into #2 & #4 mount bracket. The boat harness is shaped like a barrell on the end and plugs into #1.
    Fix minor things (replace wear items for preventative maintenance.) that cause major problems before they break.

  14. #14
    Join Date
    Dec 2006
    Location
    Lake St Clair /Detroit, MI, USA
    Posts
    335

    Default "Duh ..ok thanks, I understand

    "Duh ..ok thanks, I understand now..you talking aob the electircal connection. I was thinking there was a corroded water connection/plug. DUH!! Will do. Thanks Guy!"

  15. #15
    Join Date
    Dec 2006
    Location
    Lake St Clair /Detroit, MI, USA
    Posts
    335

    Default "Ok Latest update. Finally go

    "Ok
    Latest update. Finally got a chance to take the boat out. The temp gauge does work but it moves so much fresh water the temp of the theromstate housing never gets warm enough to move the gauge until the engine is turned off. It stayes cool tothe touch while the engine is running. When tirned off and no cooling water is pumping the gauge climbs to 150. While the engine is running , although the thermostate housiing runs ccol to the touch the water runners adjacent to the themostat in the intale manifold are hot to the touch. Any ideas now? There is a copper semicircular baffle in the thermostat housing but best I can see it only goes in one way. On another issue there is an alrm that seems to buzz all the time under the dash. It has a brown wire with a blue strip, same as the one that goes to the warning alarm heat sensor however the heat sensor is on the oposite side of the thermo housing and if its running that cool to the touch it can't be over heating. Also the oil pressure gauge is readng good pressure.and when I pull the brown with blue striped wire off the terminal on the warning alarm heat sensor the buzzer keeps buzzing so it must be getting a signal/completeing a curcuit somewhere else? I believe the buzzer actaully starts making a buzz from the time the key is initally turned on however sometimes you don't notice because the exhaust is above the waterline and quite loud. Suggestions??"

  16. #16
    Join Date
    Aug 2006
    Location
    SW Ohio, USA
    Posts
    10,396

    Default Test the thermostat; was it in

    Test the thermostat; was it installed correctly?
    Fix minor things (replace wear items for preventative maintenance.) that cause major problems before they break.

  17. #17
    Join Date
    Nov 2008
    Location
    Cocoa, FL, USA
    Posts
    58

    Default "On my 2000 5.0L, my manual st

    "On my 2000 5.0L, my manual states the alarm under the dash is for detecting 3 abnormal conditions:
    a. Low engine oil pressure.
    b. Low Drive fluid in reservoir.
    C. Overheating.

    Any of these symptoms will cause the engine to shut off to prevent damage.

    The alarm is supposed to sound when the ignition switch it turned to the 'ON' position as a test, like those idiot lights on a vehicle dash.

    You may have a faulty oil pressure sensor or faulty alarm, either is a cheap fix if that is the problem. Also, you may want to check engine temp while running with a digital heat gun. I'm not sure if you can rent/borrow this item?"

  18. #18
    Join Date
    Dec 2006
    Location
    Lake St Clair /Detroit, MI, USA
    Posts
    335

    Default I saw that too in my manual.

    I saw that too in my manual.
    I don't think it is the oil pressure because the gauge reads 40 psi. Is there a different sender for the oil pressure to the alarm vs the pressure gauge and if so how do I identify it?

    Can't be the alarm for overheating as when I remove the wire from the heat sender the alarm still stays on.

    The alarm goes on when you turn on the key and stays on.

    Could be the drive fluid resevoir if the float or sensor is faulty but the resevoir is full. How would I check for this?

    Frustrating stuff for sure.

  19. #19
    Join Date
    Dec 2006
    Location
    Lake St Clair /Detroit, MI, USA
    Posts
    335

    Default "Also, are y sure there is an

    "Also, are y sure there is an auto shut down function? When I did overheat recently due to decomposition of the water pump rubber impeller the engine did not shut down automatically. It had to be shut down manually."

  20. #20
    Join Date
    Nov 2008
    Location
    Cocoa, FL, USA
    Posts
    58

    Default "After checking with the wife

    "After checking with the wife (she's younger and has a better memory), she confirmed what you say about not shutting the engine off, but this was when I had the low drive fluid alarm. Then engine remained running but the alarm remained on. On the reservoir low level mark, my fluid was at the bottom of the mark and it set off the alarm.

    I also had the oil sending unit let go due to corosion from an exhaust gasket while out in the river, sprayed oil all over the engine and cover, and this definetely shut-down the engine, the alarm sounded, and it would not fire back up."

  21. #21
    Join Date
    Dec 2006
    Location
    Lake St Clair /Detroit, MI, USA
    Posts
    335

    Default Ok I have an alarm buzzer that

    Ok I have an alarm buzzer that does not want to go off. It goes on when I turn on the ingnition key and never goes off. I suspect the float in the outdrive reservoir. What other alarm would come on before you start the boat and stay on? I have good oil pressure and it has a new temp gauge sender and is not overheating. I'm trying to isolate the circuits out one at a time. How can I test out the float alarm? Is it a naturally open or closed switch? If i disconnect the wiring to the float will it kill the alarm?
    Secondly..where is the oil pressure alarm sensor located? What color is the wiring to it? If I disconnect this wire I assume I will kill that circuit?
    Finally..the alarm itself. I assume that if i kill all those circuits it will kill the alarm.
    Don't you just love electrical glitches!!!
    Thanks all

  22. #22
    Join Date
    Dec 2006
    Location
    Lake St Clair /Detroit, MI, USA
    Posts
    335

    Default Ok I have an alarm buzzer that

    Ok I have an alarm buzzer that does not want to go off. It goes on when I turn on the ingnition key and never goes off. I suspect the float in the outdrive reservoir. What other alarm would come on before you start the boat and stay on? I have good oil pressure and it has a new temp gauge sender and is not overheating. I'm trying to isolate the circuits out one at a time. How can I test out the float alarm? Is it a naturally open or closed switch? If i disconnect the wiring to the float will it kill the alarm?
    Secondly..where is the oil pressure alarm sensor located? What color is the wiring to it? If I disconnect this wire I assume I will kill that circuit?
    Finally..the alarm itself. I assume that if i kill all those circuits it will kill the alarm.
    Don't you just love electrical glitches!!!
    FRustrating!!!!!!!!!!!!!!!!!!!!!!
    Thanks all

  23. #23
    Join Date
    Jun 2008
    Location
    Island Heights, NJ,
    Posts
    2,605

    Default RE: "Can't be the alar

    RE: "Can't be the alarm for overheating as when I remove the wire from the heat sender the alarm still stays on."

    1) sender for the gauge and for the alarm function are two different sensors.
    2) Engines often overheat after the impeller self distructs and a new one is installed... bits of it get lodged in inconvenient places in the engine and impede water flow.
    Capt Bob
    1969 23ft ChrisCraft Lancer
    Merc 5.7L 260HP/ Volvo 280
    1972 22ft Bristol
    Honda 7.5HP 4 stroke Long shaft

  24. #24
    Join Date
    Dec 2006
    Location
    Lake St Clair /Detroit, MI, USA
    Posts
    335

    Default "I agree and understand but th

    "I agree and understand but the alarm is going off when I turn the ignition key on before the engine is even turned on so its ice cold at that point so it can't be sensing heat and, both the heat alarm sensor and the gauge sensors are located opposite each other on the thermostat cover,are new, and neither kill the alarm when the wires are removed but will kill power to the temp gauge when that sensors wire is removed."

  25. #25
    Join Date
    Aug 2006
    Location
    SW Ohio, USA
    Posts
    10,396

    Default My engine uses tan/blue stripe

    My engine uses tan/blue stripe wire. All sensors are switches on a parallel circuit. Any of them can turn on the alarm. Your alarm is either bad or you have a bad oil pressure switch or a short in the circuit. Trace the wire.
    Fix minor things (replace wear items for preventative maintenance.) that cause major problems before they break.

  26. #26
    Join Date
    Jun 2008
    Location
    Island Heights, NJ,
    Posts
    2,605

    Default The "buzzer" on my 5.7

    The "buzzer" on my 5.7 MIE sounds immediatly when the ignition is switched on and stays on until the engine starts and the oil pressure comes up to "par".
    Capt Bob
    1969 23ft ChrisCraft Lancer
    Merc 5.7L 260HP/ Volvo 280
    1972 22ft Bristol
    Honda 7.5HP 4 stroke Long shaft

  27. #27

    Default Erratic temp gauge on Ford 233

    Erratic temp gauge on Ford 233 Mercruiser inboard circa 1977(?). At medium cruise temp runs normal but then will jump to just less than redline. When I then shut the engine down and restart after 1 or 2 minutes temp indicate normal for a minute (+ or -) and then jumps to just less than redline again. Replaced sender unit and tightened connections on back of temp gauge. No help. Reasonably sure that engine is not overheating.

  28. #28
    Join Date
    Aug 2006
    Location
    SW Ohio, USA
    Posts
    10,396

    Default "steve: You should start a

    "steve:

    You should start a separate posting for more to see and respond while not interfering w/the one you added a message.

    Get a laser thermal temp. gun and take temp. readings at the base of the T'stat hsg., exhaust manifolds, risers and elbows. You should be able to lay your hand upon the elbow tops w/o it burning.

    When was the OD impeller and T'stat last replaced?

    Thermostat may be opening late or partially. I suspect the impeller may be worn and/or the manifolds, risers and elbows may be contaminated w/rust and mineral deposits and restricting water flow out of the engine."
    Fix minor things (replace wear items for preventative maintenance.) that cause major problems before they break.

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