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  1. #1
    Join Date
    Feb 2018
    Location
    Conroe, TX
    Posts
    1

    Default Water temp go up and down on a Mercruise 502 engine

    My boat has twin 502 with 165 hours. Both are running great, and the water temperature gauges both maintain a 165 temperature. But one engine started having the water temperature gauge high to 230 (moves fast) then it goes down to 0 and then back climbs back up slowly. At first, I thought the gauge may have problems, but I noticed that oil temperature slowy climbs up and starts to get hot. I did replace the
    thermostat but no change. My next step is to use a garden hose on the fresh water connections. Any other suggestions?

  2. #2
    Join Date
    Dec 2015
    Location
    maplevalley WA
    Posts
    5,049

    Default Re: Water temp go up and down on a Mercruise 502 engine

    Get a IR temp gun and shoot different parts of the engines and compare temps. It could be simple as a poor connection pn the temp senser a good IR gun is handy to have for on the fly diagnostics.

  3. #3
    Join Date
    Dec 2006
    Location
    Chaumont Bay, N.y., USA
    Posts
    5,567

    Default Re: Water temp go up and down on a Mercruise 502 engine

    Ayuh,...... Change the raw water pump impeller,.....

    That's the 1st step in any overheat diagnosis,.....
    Any Grease is Better,... Than No grease at All....

  4. #4
    Join Date
    Sep 2008
    Location
    Maryland - USA
    Posts
    7,370

    Default Re: Water temp go up and down on a Mercruise 502 engine

    I was gonna ask when the raw water pumps were last serviced........

  5. #5
    Join Date
    Sep 2010
    Location
    Jersey Shore
    Posts
    4,944

    Default Re: Water temp go up and down on a Mercruise 502 engine

    When the temp gauge jumps around like that it is usually caused by air being introduced into the cooling system.
    Chris
    Dockside Marine Services
    Jersey Shore.
    Mercruiser/Mercury Certified
    Let the insanity begin.

  6. #6
    Join Date
    Sep 2003
    Location
    New Tripoli, PA, USA!
    Posts
    15,709

    Default Re: Water temp go up and down on a Mercruise 502 engine

    I'm with kimcrwbr1: Buy or borrow an infrared temp gun and see what's really happening.

    Temps don't go up that fast!

    Jeff

  7. #7
    Join Date
    Nov 2011
    Location
    tennessee
    Posts
    3,026

    Default Re: Water temp go up and down on a Mercruise 502 engine

    Raw or closed system?
    Pappys Sales and Service
    Owner and Factory Certified Technician
    Former racer KDBA (Kentucky Drag Boat Association)

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