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Mercury oil pump and compression

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  • Mercury oil pump and compression

    I am looking at a 1999 fish n ski with a 150 Mercury outboard. The owner is running premix because the factory oil pump is shot. He says it is a plastic mechanical pump that wears out, is that true? seems like a terrible design. He bought a $500 electric oil pump that he leaves disconnected, I have a concern that this motor has seen a time when oil wasn't flowing and it may have seized. Are Mercury motors any good?????
    Which leads me to the next question, what should the compression be on this motor? I want to do a compression test on it.

  • #2
    Re: Mercury oil pump and compression

    i would figure good compression readings would be in 115-125 range,however the %difference between the cylinders is more important.would like to see <10% difference on any cylinder.so if theyre reading 120,121,124,121,etc.,fine.if you get 121,124,80,121.etc.back off and go home!as for oiler,if you really want oil injection,have it hooked back up and tested.if you dont care,i would leave it off and just premix.safer in my view and what i do w/my 1988 150 xr4.mercurys,to me,are great motors.all motors have issues from time to time,but for reliability,track record,satisfied owners,you cant go wrong w/merc.compression will be deciding factor on motor.closely followed by electrical,and right with lower unit operation.all can get VERY costly to have repaired/replaced even if you can do the work yourself.be excited about buying but be cautious also.if you have little/no knowledge of outboards,take someone who does!sorry to rain on your parade,but there are shysters out there who will tell you anything.hope it works out.good luck!


    • #3
      Re: Mercury oil pump and compression

      didnt mean to get so long winded in last reply.but 1,DEFINATELY do a compression check.follow guideline as stated above for less than 10%difference in ANY CYLINDER(S).and NONE should be below 110 i wouldnt think.be sure to look at other structural issues as well(soft floors,transom,cracks,etc.)boats can be absolutely awesome to own/operate but,they can also be huge money pits!you just need to be very educated when looking to buy any used boat or at least have someone w/you that is.w/that said,try,if at all possible,to have him do a test drive ON THE WATER W/YOU.not on a garden hose if possible.check that its running,peeing,no leaks,shifts into gear(forward and reverse)easily,then buy or go home.best of luck.


      • #4
        Re: Mercury oil pump and compression

        Thanks for the info...
        I test drove the boat today, and it drove fine, it cranked right up, and idled through a no wake zone without so much as a hickup.
        A buddy of mine told me that he would premix anyway just to be sure the motor is getting fed with oil. I just can't get past the pump. I am concerned that it failed THEN he started premixing. If the compression test works out OK can I put that concern to bed?

        There does seem to be some electrical problems. One fish finder does not work, may just be a problem with the unit itself. Flasher depth finder works "half the time" and a brand new stereo quit working. This may be minor but it is giving me the hebe jeebes. What do you think this boat is worth??????


        • #5
          Re: Mercury oil pump and compression

          Call Marine Solutions at 262-524-0804 to help you get the electronic oil injection system working.


          • #6
            Sign up today
            Re: Mercury oil pump and compression

            what do you think the boat is worth is a loaded question!we cant see it.dont know what make/model it is.condition,etc.motor should be ok IF compression checks out.electrical issues can fairly easily be sorted out w/knowhow and proper testers(speaking of accessory electrical).did he pull drain plug when you loaded up?did any water exit the hole?are floors spongy anywhere?transom solid(no flex)?just saying that this boat could be worth $0(if motors shot,transom weak,etc.)to as much as probably $14000 if its all pristine,a-1,mechanically,top brand,shiny as new,etc.again,TAKE SOMEONE WHO KNOWS BOATS W/YOU!!!!!!!!!!