Water Pressure

Discussion in 'General Maintenance/Repair Questions' started by Curtis, Jan 7, 2019.

  1. Curtis

    Curtis Member

    63
    Feb 6, 2013
    San Antonio, Texas
    320 Sundancer 2004
    Previous 280 Sundancer
    Twin 8.1 (496 Mags) w Bravo III drives
    I have a 2004 320 with 8.1s. Last Friday, the Port engine would not run over 3000 RPM and I could smell unburned fuel. I changed the plugs and she ran like a top, up to about 4400 RPM, but mostly about 3400 rpm for about 10 minutes. The computer then told me I had no water pressure on the port engine. It was a bit warmer than the starboard engine but not excessively hot, 161 degrees port vs 147 starboard. I could have coincidentally trashed an impeller but is it possible I knocked the water pressure sensor loose? Can anybody tell me where to look for the sensor and what it Looks Like? I would like to trade the sensor from the starboard engine to the port engine if it is reasonable to do so. Thoughts?
     
  2. WV 320 Dancer

    WV 320 Dancer Well-Known Member

    802
    Oct 28, 2018
    2003 Sea Ray Sundancer 320
    Twin 350 MAG - V Drive
    160 is perfect for the 496... I had one for 15 years and mine ran at 160 the entire time we had it.
     
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  3. LG111

    LG111 Active Member

    606
    Jan 4, 2015
    NW
    44 Sedan Bridge - 07
    Black Hull
    QSC500’s
    The sensor is on the raw water pump. Port side of lower engine. Close the raw water petcock and remember how many turns out and position. Repeat when replacing. My 8.1s both run at 154 in 40 degree water. If a sensor goes out it earthier pegs 40 PSi or zero. Check the hole in the sensor for debris like a grain of sand. Sometimes that causes issues. However it your temp has increased some, I'd say your impeller is failing or the pump is worn from the impellar. From there I'd check the cooling system for a slight blockage...

    Hope that helps.
     
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  4. Korkie

    Korkie Active Member

    877
    Feb 2, 2016
    Leonardtown, MD Potomac River / Chesapeake Bay
    340 Sundancer 2006, Garmin 7612, xHD Radome
    Merc 496 Mags
    Bravo III Drives
    What are your water pressure sensor readings at idle, 1200 and 3200 rpms? Should be around 3-4psi at idle, 10 or so at 1200rpms and high teens/low 20s at 3200, 20s at 4000. Motors and gauges vary but the point is pressure should go up close to these numbers to which show adequate pre load of water to the pump. The other possibility if all else looks good is bravoitis, especially in salt water. It is the plugging up of the tube that goes through your outdrives restricting water intake. Will present as low water pressure. Your can check for it by removing the plate that comes from the outdrive at the transom. Will be obvious if it is occluded. There is a fix for it from Mercury. Replace tube in outdrive, or you can install thru hulls as many others do.
     
  5. Curtis

    Curtis Member

    63
    Feb 6, 2013
    San Antonio, Texas
    320 Sundancer 2004
    Previous 280 Sundancer
    Twin 8.1 (496 Mags) w Bravo III drives
    My reading went to 0 psi. Unfortunately, I can’t say what the engines normally run because up to now, it hasn’t been an issue and I haven’t paid attention. I will pay more attention in the future. Thankfully, the warning systems worked this time.
     
  6. Curtis

    Curtis Member

    63
    Feb 6, 2013
    San Antonio, Texas
    320 Sundancer 2004
    Previous 280 Sundancer
    Twin 8.1 (496 Mags) w Bravo III drives
    Mine went to zero.
     

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