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  1. #1
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    Optimax over cooling

    Hi I have a 2004 Optimax 115 1.5l OT869845.

    Which has an overcooling issue, when I put her in for the season she temps when straight up to 143f as normal the would drop to 90 once under way. Then all a week it won't make normal temps at idle only around 42, had a new water pump and I have since replaced thermostat, and poppet diaphragm and the idle temp went back to normal, but after the first run when returning to idle it is stuck any where between 100-115.
    Water pressure at idle is varies between 4 - 4.5 psi straight after installing the new thermostat and poppet diaphragm whe idle pressure was just over 5psi but has droped slightly it was too rough for a wide open throttle run but around 4000 rpm it was just over 10psi.

    Any ideas I was wondering if I should replace the popet valve spring but not sure if that would help or not.
    TIA
    Last edited by chood98; 05-15-2022 at 09:22 AM.

  2. Member
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    #2
    water psi is normal , what is surface temp of lake water , p/n of thermostat ???
    .................................................. ...the scariest thing in life is the unknown ...................................

  3. Member
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    #3
    Seawater is 65f thermostat is part no 833072004

  4. Mercury 3L/4 Stroke/Verado Moderator EuropeanAM's Avatar
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    #4
    May simply have debris hung in thermostat or poppet (again).

    Note: If your water pressure were HIGHER, we would be looking at debris under the powerhead/adapter plate area.


    Dual Mercury Master Technician- for Mercury Outboards, Mercruiser and Mercury Racing at European Marine in Greenville, SC.
    Still consider myself a "Marine Apprentice" after 47 years (learn something new every day).
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  5. Member
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    #5
    Thanks Don I will strip it down again and check, you don't happen to know the poppet spring uncompressed length so I can check it while it's apart?
    Last edited by chood98; 05-18-2022 at 04:20 PM.

  6. Mercury 3L/4 Stroke/Verado Moderator EuropeanAM's Avatar
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    #6
    No, I do not.


    Dual Mercury Master Technician- for Mercury Outboards, Mercruiser and Mercury Racing at European Marine in Greenville, SC.
    Still consider myself a "Marine Apprentice" after 47 years (learn something new every day).
    Mercury Parts, Mercury Outboards, Smartcraft & Accessories, Injector Service, TDR Reeds- BBC Sponsor

  7. Member
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    #7
    We striped it down and cleaned it again but still the same we so replaced the poppet spring and thermostat just incase and it is now warming up properly.
    But I just want to make sure these temps are right the sea temperature is currently 60f and it will idle around 144f running off the plane between 2000-3500 revs it runs at 140-156f and at 3700-4500 revs it is running at around 112f does that sound right or something else wrong
    Last edited by chood98; 06-17-2022 at 05:10 PM.

  8. Mercury 3L/4 Stroke/Verado Moderator EuropeanAM's Avatar
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    #8
    That's normal.


    Dual Mercury Master Technician- for Mercury Outboards, Mercruiser and Mercury Racing at European Marine in Greenville, SC.
    Still consider myself a "Marine Apprentice" after 47 years (learn something new every day).
    Mercury Parts, Mercury Outboards, Smartcraft & Accessories, Injector Service, TDR Reeds- BBC Sponsor