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Expansion Tank Coolant Pressure

Discussion in 'Technical Discussion' started by CSkipR, Nov 3, 2013.

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  1. CSkipR, Nov 3, 2013
    #1
    CSkipR

    CSkipR Member

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    The above alarm went off this morning and went off before we left for the Bahamas in May. No overheat issues everything shows okay. Reset and be on the way. I suspect a sensor that is going bad or loose wire on the sensor. The engines are Man CR900. Its the starboard engine. Where is that sensor located?
    Thanks, Skip
  2. Capt Ralph, Nov 3, 2013
    #2
    Capt Ralph

    Capt Ralph Senior Member

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    Skip
    We are having a similar problem on a customers boat in Jax.
    #1 thing our MAN rep ask us to do was when the alarm came up, do not clear it. Idle down, turn the engine off. Then restart. This saves the alarm and unseen data in memory for further analysis.
    There are a couple of pressure sensors in the coolant side of the CRM system.
    Last year the other MAN had a pressure alarm. One of the expansion tank caps was leaking, new cap fixed that problem.

    If you have the big Man CAN displays, you can compare some coolant temp, flow & pressure data between the mains when the error happens. The two won't be identical matches, but if there is a real problem, you will see a gross difference in data and know a real problem is trying to tell you something.
    Chances are, it's a (expensive) sensor.
  3. CSkipR, Nov 3, 2013
    #3
    CSkipR

    CSkipR Member

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    Ralph,
    Are Man engine gauges read fine so I'm sure it is the sensor. Just trying to locate it so I can check wiring for loose connection.
    Thx, Skip
  4. Capt Ralph, Nov 3, 2013
    #4
    Capt Ralph

    Capt Ralph Senior Member

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    I have the manuals with pics & IPB on PDF. PM me a e-mail address and I'll squirt it to you.
    ,rc
  5. CSkipR, Nov 3, 2013
    #5
    CSkipR

    CSkipR Member

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    Thanks Ralph that's perfect.
  6. Capt J, Nov 3, 2013
    #6
    Capt J

    Capt J Senior Member

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    Did you remove the cap and check coolant level? If you did, there should be a small shrader valve, that you should put an air pump and pump it up to 16lbs. If you didn't pump it up, then sometimes an alarm will go off. Also the coolant caps should be changed every 2 years, and this can also be the cause. If not, look at the sensor which should be at the top of the expansion tank.
  7. CSkipR, Nov 3, 2013
    #7
    CSkipR

    CSkipR Member

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    Capt J,
    Yes checked the coolant level it was fine. I haven't pumped up the shrader valve. Caps were changed about 6 months ago. Thanks I found the location of the sensor from (Rcrapps) and it doesn't look like any loose wires. Will probably continue to use boat and see if it happens again. If it does may change sensor from the other engine. Unfortunately this problemy only happens every now and then. All the temp and pressure readings are fine on the Man gauges.
  8. Capt J, Nov 3, 2013
    #8
    Capt J

    Capt J Senior Member

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    Every single time you open the cap on the resevoir, you should pump up the expansion tank with air, or there is a good possibility that this alarm will go off.....
  9. T.K., Nov 4, 2013
    #9
    T.K.

    T.K. Senior Member

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    Gentlemen, the expansion tank pressure on the MAN engine needs to be between 0.7bar and 0.9bar and not higher when at normal operating temperature which is approx. 87degc. You should not pressurize the expansion tank if you open the cap while the engine is cold and was not run. If you do so, you will over pressure the expansion tank and the alarm will sound because the pressure will exceed the 0.9bar limit when the engine reaches it's operating temperature of 87degc. The expansion tank should be manually pressurized to the figures mentioned above through the shrader valve fitted to the top of the expansion tank, only if the cap is opened while the engine is hot and was or is running. Also, please ensure that the expansion tank caps are well locked. They have two locking stages.

    I have twin MAN 1200 CRM engines on my boat and the above also applies to the 900 CRM engines.
  10. Capt J, Nov 4, 2013
    #10
    Capt J

    Capt J Senior Member

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    If there is too much air pressure, the expansion tank cap allows it to disappate and keep it at the maximum pressure that it is made for 0.9 bars? If you're doing a delivery or running the boat everyday, the next morning the engines will not be at ambient air temperature. They may be say 110F, and when you open the cap you're allowing some air to escape, do it 5 days in a row and it may cause the low coolant pressure alarm to sound.

    If the engines are cold, on most of the MAN engine models it is not necessary to pressurize it. However, it does not hurt to pressurize it either, as the coolant caps will allow the excess pressure to escape and close when it is at exactly the correct pressure.