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  1. #1
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    96 225 Offshore overheating

    1996 Mercury 225 CXL, 0G408399, Quicksilver SS 14-3/4 x 21 prop, 1989 22’ Boston Whaler Outrage, this is a salt water boat that sits on a mooring and used a 1-4 days a week depending on weather and free time, gets flushed at the end of the year. Motor was given to me in spring 2020 with unknown hours (this one is counter rotating and someone bought the other with all the gauges and info) and have not had an issue till now. I've spent quite a bit of time digging through forums and the most common questions and answers to my issue have brought to this forum.

    I noticed the pee stream was getting weak towards the end of last year, usually a race horse after tstats open up (last big exercise was pulling boats off a beach after a storm, had a knick in the prop so I’m sure it sucked up some sand and bits)… old impeller was totally fine but did a full water pump kit (impeller, gaskets, plates, shaft seal) this spring and started to get overheating alarm every few minutes or so at 1/2 throttle 2 people on board (mid 30s mph)… more passengers or faster speeds alarm would come on sooner, so I ran the boat for a while keeping it just barely on the throttle (15-20mph) with no issues.

    Past few weeks I have been trying to further chase the issue. Rechecked the water pump, new thermostats and gaskets, new poppet, with no improvement. Took the thermostats out and back flushed with a garden hose and after a few minutes something released and went back to normal racehorse pee stream. It did improve and gained another ~10mph and can go longer till the over heat alarm comes in. Starboard bank runs ~15-20* hotter once warmed up (145port - 165starbord idling/ 155port - 230starbord right after alarm comes on ripping it around). Port side seems dead stable at any throttle and never reads over 155-ish. Starboard side right after alarm, 230 reading was at the sensor, bottom cylinder head was mid 160s, top cylinder head was 180s as well as right at the thermostat. The hot spot was right between the cylinder heads where the sensor is. I have Ohmed and checked the manual to see that it’s reading correctly even though I don’t have a gauge. After a minute of idling or turning the key off for five seconds the alarm turned itself off.

    I have heard about issues in the exhaust plate; gasket issues leading to exhaust and or pressure entering the water intake, and carbon buildup. I don’t want to pull the boat and remove the powerhead midseason so I’m fine running it just on plane till I can pull it out in a in a couple months. My second thought is pulling the head to see if there is a chunk of something in one of the cavities or jackets? Is there one area I should start with and look at first? When I pulled the hoses after the thermostat to do a second flush and check for flow, I did notice the port has a smidge more flow and there was also light exhaust puffs coming up the hose to the thermostats, very minimal and equal both sides at idle, not sure at throttle or load but figured its worth a mention.


    Water flow diagram for the 3L EFI but seems to be identical to my carbed if its any help

    <EDIT- ANNOUNCEMENTS>







    Thanks for any ideas or suggestions
    -Colin



    Last edited by EuropeanAM; 08-08-2022 at 10:32 AM.

  2. Member
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    #2
    you will see puffs at hoses because of where they dump into midsection to cool it , could be blockage but id bet on gaskets under powerhead , do a leak down to check orings on cyls also
    .................................................. ...the scariest thing in life is the unknown ...................................

  3. Mercury 3L/4 Stroke/Verado Moderator EuropeanAM's Avatar
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    #3
    One other thing: You mentioned a weak "appearance" to the telltale originally, but don't mention any overheating until AFTER you replaced the water pump.

    Regardless of whether it's brand new or not: Remove and inspect the pump. At a minimum, replace BOTH gaskets and use Perfect Seal between lower gasket and housing.

    Proper orientation is CRITICAL. Impeller fins must fold correctly. DO NOT USE GREASE IN THE WATER PUMP.

    And most importantly: OEM Mercury/Quicksilver Parts/Components ONLY. There IS a difference.


    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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  4. Member
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    #4
    Don what do u put on impeller, I have always used a very light coat on inside of housing.
    Ron Fears
    Stroker/300XS
    1E003823

  5. Member Especial Bryanmc57's Avatar
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    #5
    Quote Originally Posted by DewRonInc View Post
    Don what do u put on impeller, I have always used a very light coat on inside of housing.
    Not Don, but Dawn dish soap works great.


    Honora Primum Vel Nullum Omnin Honorem

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    #6
    Quote Originally Posted by Bryanmc57 View Post
    Not Don, but Dawn dish soap works great.
    ^^^^+1 and what Don recommends.^^^^
    _______

    Phil
    '09 Hewescraft ProV
    '09 150 Optimax


  7. Mercury 3L/4 Stroke/Verado Moderator EuropeanAM's Avatar
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    #7
    ^^^ +2 ^^^


    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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  8. Member
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    #8


    Quote Originally Posted by EuropeanAM View Post
    One other thing: You mentioned a weak "appearance" to the telltale originally, but don't mention any overheating until AFTER you replaced the water pump...


    I only idled the boat to the ramp and pulled it in the spring when I did the water pump so I never ran it (after what I assumed was sucking up sand/muck) to see overheat.


    In some of the flow chart diagrams online I see there are “rubber water dams” between the cylinder walls in the block, and a note saying if missing may result in uneven cooling of cylinders. Is anyone familiar with these or have any pictures? Is it a plug or a diaphragm to control flow? From what I can see on eBay blocks is a rubber dowel looking piece. I find it hard to believe a piece of debris that was sucked up could push one of these out. Wondering if this might be why there is a spike between middle and top cylinders right at the temp sensor… How is the gasket under the powerhead effecting just the starboard bank, and for the most part right between the cylinders where the sensor is?


    Screen Shot 2022-08-13 at 1.42.40 PM.png


    s-l1600.jpg




  9. Mercury 3L/4 Stroke/Verado Moderator EuropeanAM's Avatar
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    #9
    There are three (3) of them in your block based on the picture you posted (above). Look between the cylinders- it's simply a long, rubber "plug" (Deflector).


    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