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Fluctuating Coolant Temperature Man CR900 V8

Discussion in 'Technical Discussion' started by CSkipR, Jun 5, 2017.

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  1. CSkipR

    CSkipR Member

    Joined:
    Aug 16, 2008
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    Location:
    New Smyrna Beach, Fl
    I'm getting some fluctuation on my Man starboard engine temperature gauge where temp goes back and forth between 192-194. Other engine is running at 190 which is where they both use to run at cruise. Both heat exchangers were taken off 4 months ago and cleaned. I'm not getting an alarm but think it maybe the sensor since its fluctuating. Since I'm in the Bahamas I don't want to exchange the sensor from the other engine since I will have to drain the coolant in both. Anyone know the sensor number for this engine? Opinion on my sensor thought as to this issue. Thanks
  2. chesapeake46

    chesapeake46 Senior Member

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    Assuming cable length dos not affect calibration, can you relocate the wires instead of the sensors ? extend the cables, temporarily ?
  3. Pascal

    Pascal Senior Member

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    Have you verified that the reading is accurate? Check with an ir thermometer to know whether it s the sensor or if the temp is high

    If it s not the sensor then basic troubleshooting. Impeller, restriction somewhere etc

    I don't know anything about mans but usually on big cats the first symptom of an impeller or restriction is slightly higher gear temp
  4. Capt J

    Capt J Senior Member

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    It's still well within the range. It's probably just between the 2 values and bouncing back and forth.....the MAN coolant temp senders like to show mostly even numbers for some un-apparent reason.......It could be impellor, sensor, etc...... a ground.....who knows.....at this point maybe take the impellor cover plate off and visually inspect, and check coolant level.
  5. CSkipR

    CSkipR Member

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    Location:
    New Smyrna Beach, Fl
    I should have mentioned I shot it with IR gun and it did show a lower temperature. Because we were running and I was being bounced around it was hard to get an exact reading. Impeller and coolant are good. Yes it is within the range just frustrating to have a variance from the other engine when they both use to be the same. Going to order a sensor and change out. Will report back when completed. Only other thing I can think of is the thermostats. After the thermostats (3 ea eng) were changed the reading when starting to warm up at idle speed are more than 15 degrees different until I reach cruise.
  6. Capt J

    Capt J Senior Member

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    Shoot behind each thermostat with your IR gun and see if one is stuck open or stuck closed.....

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