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  1. #1
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    Water Temp Gauge problem - HELP!

    1997 Freightliner FLD120 Day Cab
    12.7L S60 Detroit Diesel w/ about 850,000mi

    My water temperature gauge [the needle] will bounce around and fall and spike in temperature (the engine will be at normal op temp). It will randomly do this..sometimes it will fall all the way to down "nothing" like the truck is shut off and that will cause the CEL, Shut Down, & Water Temp warning lights and buzzers to all come on..then randomly the gauge will shoot up and then settle back to normal temp reading(the warning lights/buzzers quit once it comes back up)..I replaced the water pump awhile back...and I recently replaced the water temperature sensor..could it be a bad/faulty sensor?...what else could this be? The computer? Also recently, when it had one of its little episodes doing that, the oil pressure light was coming on with those...What is going on? Also, I've noticed it likes to do it the most the first time its getting up to temp in the morning...but once I've arrived somewhere and shut off the truck, then on the way back out the gauge will work fully normal...almost like its a cold issue or once everything is hot it doesn't do it?

    I'm stumped..is the gauge itself? electrical issue? Computer??..

    Thanks for any help!

  2. #2
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    Chad try checking the wires under the hood going to the sensor. tug on the wire to make sure it fully connected. does it happen under a load or empty? I know u said cold.

  3. #3
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    Quote Originally Posted by cdub304 View Post
    Chad try checking the wires under the hood going to the sensor. tug on the wire to make sure it fully connected. does it happen under a load or empty? I know u said cold.
    Hmmm...You know what. I think every time it's doing it I'm under a pretty good load! Cuz empty I don't think it's doing it..why? And okay the wires that go into the temp sensor itself?

  4. #4
    Road Train Member Heavyd's Avatar
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    Check for rubbed wiring for the temp sensor and unplug it and check the terminals inside the connector for spread or corroded pins.

  5. #5
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    Okay, I'm out of town tonight but I'll check that plugs pins soon.


    thanks for the help so far guys, keep the advice coming!! This issue is so frustrating!

  6. #6
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    Okay well I checked tons of wires and the wire temp sensor plug and everything looked fine. I even took the dash piece out for the gauge and all those wires look fine. Should I try replacing the actually "water temperature" gauge pod itself? Can that go out? Thanks.

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    the dash gauge gets it's signal from the sensor in the thermostat housing. the sensor in the head on pass side sends signal to e.c.m. if your also getting other codes, oil temp, low oil pressure e.t.c. it is a good chance it is a ground wire problem. somewhere.

  8. #8
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    Quote Originally Posted by heavyhaulerss View Post
    the dash gauge gets it's signal from the sensor in the thermostat housing. the sensor in the head on pass side sends signal to e.c.m. if your also getting other codes, oil temp, low oil pressure e.t.c. it is a good chance it is a ground wire problem. somewhere.
    Well the oil temp one only came on with it once for a few seconds..other than that it's been just all the water ones. It seems to like to do it when going up a hill it will send off the buzzer for a few seconds and then never do the buzzers again, but the gauge will just act haywire and not show accurate readings and be basically floating around reading like 100 then spike to 200 then to 150...could it be the low level sensor in the overflow tank? I had that unplugged a little bit ago and the check engine light never came on...it used to..how weird is that?

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    The water level sensor would have nothing to do with your dash gauge i.m.o. running low of coolant would not affect your temp gauge. the water temp sensors share the same ground. if 1 wire from any one of the sensors has a bad ground, it could affect other wires on that same ground line. affecting other sensors, causing them to go erratic, even though nothing is wrong with the truck or the sensors. I have had the same problem before. have similar one now. a bad corroded battery cable, or cables, jumper cable, ground at starter, frame, e.t.c. can cause or contribute to your problem.

  10. #10
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    Quote Originally Posted by heavyhaulerss View Post
    The water level sensor would have nothing to do with your dash gauge i.m.o. running low of coolant would not affect your temp gauge. the water temp sensors share the same ground. if 1 wire from any one of the sensors has a bad ground, it could affect other wires on that same ground line. affecting other sensors, causing them to go erratic, even though nothing is wrong with the truck or the sensors. I have had the same problem before. have similar one now. a bad corroded battery cable, or cables, jumper cable, ground at starter, frame, e.t.c. can cause or contribute to your problem.

    Okay. I do need to check the batteries and cables maybe I'll do that today. I ran out of time yesterday and forgot to look at those. I spent so much time on the engine bay checking all wires for any obvious looking bad wires. Do you know where I could possibly find the bad ground??..electrical problems suck

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