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  1. #1
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    water pressure question.

    96 Mercury 200efi, had it for 9 months now, when purchased idle pressure was about 2lbs, wot was about 8lbs. Replaced complete water pump, thermostats and poppet valve. Idle pressure is about the same , wot is a little better but I think still too low at about 12lbs. I am about to install the mercury high speed inlet kit, but my question is this. Currently the pressure guage is plugged in inside the lower unit, if I plug it off in the lower unit and tap it into the crossover hose between the heads would that give a more accurate reading or no ? Thank you for any info.
    2000 Tr21, 225 EFI

  2. Member
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    #2
    The tube going to the lower unit should be the speedo tube, which also relies on water pressure. Make sure you are tracing the right tube. The speedo tube and water pressure tube look the same. My 2002 model has the water pressure tube connected to a fitting under the starboard cylinder head. 12lbs at WOT is the minimum spec but maybe ok.
    Mercury 2002 200hp Carbed Saltwater
    OT566776
    2002 Cape Horn 22' Bay

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    #3
    Well I didn't even think of the speedo, I always watch the speed on the lowrance. Thank you.
    2000 Tr21, 225 EFI

  4. Member
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    #4
    I am not a Mercury owner but first, you should borrow a known good gauge and make a simple tee fitting, and check it against your gauge. It can be done in the boat or on a test bench if you have a low pressure source.

  5. Mercury 3L/4 Stroke/Verado Moderator EuropeanAM's Avatar
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    #5
    Please take a moment to review the Announcements at the top of the forum, and provide the Required Info with your post. Thanks!

    If you engine is indeed what you think it is- water pressure is tapped into a fitting at the very top of the block (behind the flywheel). NEVER to the gearcase, NEVER to the thermostat housing hoses.


    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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    #6
    Water pressure gauge is tapped from here...see brass fitting on top of motor..

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    Bruce Phillips
    1995 190 DC champion ......1995 200 xri merc

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    #7
    Thanks Bruce. I checked it the other day and it is tapped in right there behind the flywheel. Iyesterday I put on the mercury high speed inlet kit. Took it out today and no change in pressure. I guess my next step will be a new guage and see if that's the problem. I have a sneaky feeling it maybe something else, the reason for that is I recently replaced the gasket on the exhaust cover and upon inspection I found 2 water ports blocked by clear silicone, I have no idea why clear silicone would be inside a motor, it looked alot like window caulk. I wonder if there could be a partial blockage elsewhere.
    2000 Tr21, 225 EFI

  8. Mercury 3L/4 Stroke/Verado Moderator EuropeanAM's Avatar
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    #8
    If you had NO change in pressure with the high speed scoop kit, I would suspect either the gauge itself OR misassembly of some component (or a massive leak somewhere, such as the powerhead gasket).


    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

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    #9
    I would pull the lower unit back off and recheck the water pump assembly...you did replace all 3 gaskets didn't you.. also check that you got the right gaskets in the right place.
    Bruce Phillips
    1995 190 DC champion ......1995 200 xri merc

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    #10
    Thanks guys, yes I have replaced the complete pump system with the correct gaskets in proper place. BUT.... I now have a small leak in the power head base gasket. I think when I change that out I am going to go ahead and pull the heads also and check there just to be safe. I agree there seems to be something not quite right somewhere.
    2000 Tr21, 225 EFI

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    #11
    a compression test or better yet a leak down test would tell if you have a head gasket leaking, as for silicone someone may have used it inside wp at onetime (no no ), check the hose all they way from mtr to gage for pinch or dirt , blow it out with compressed air,or run a new one,dont just change base gasket change adapter plate gasket also possibly resolve ploblem, been there seen this,check poppett valve and block grommet also hope this helps ya joe
    .................................................. ...the scariest thing in life is the unknown ...................................

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    #12
    Thanks Joe, will do.
    2000 Tr21, 225 EFI