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    Marvel Mystery Oil-gctid810400

    Quick background:

    Engine (2005 5.0 MPI) been running a little higher oil pressure than it was last year.

    It used to run 60psi at 3500 RPM and now its running ~70 at 3500 and then somewhere between 70 and 75 at WOT currently. I do not know what WOT psi was last year as I don't really ever run WOT. It also currently idles ~52 psi cold or warm doesn't matter.

    All I have done is an oil change since last year and this year. Some say that psi is just fine, some say its a little high. I'd rather be cautious than sorry.

    I was told to remove a quart of oil and add a quart of marvel mystery oil. Idle it to operating temp and then let it idle for another 20 minutes, then change the oil out again to remove any obstructions from debris.

    I'm wanting opinions on this. Is it safe? Effective? Waste of time/money? What do you guys think?
    2002 Bayliner Capri Sport 195 Mercruiser 5.0L Alpha I Gen II

    #2
    You can use1 qt of transmission oil too. It is a very high detergent type.
    -Boatless-

    Bryers Cottage Marina
    Harrison Twp, MI

    Comment


      #3
      Anything to look out for while doing this? Will it actually remove an obstruction? Any risks to doing this?
      2002 Bayliner Capri Sport 195 Mercruiser 5.0L Alpha I Gen II

      Comment


        #4
        If the oil pressure is the same at idle when cold and when hot I would suspect the sending unit may be the culprit. I would hook up an external pressure gauge before I start dumping anything other than motor oil in the engine. If the external gauge confirms what the dash gauge is telling you then you may have a blockage somewhere or your pump may be the culprit, or possibly the pressure relief valve.

        Either way, I would try not to run the engine with that high oil pressure until you figure out the cause for that reading.

        Oh, the obvious question: I assume you are using the same oil you used last year? And that you changed the filter when changing the oil?

        Comment


          #5
          "mgm1986" post=810405 wrote:
          Oh, the obvious question: I assume you are using the same oil you used last year? And that you changed the filter when changing the oil?
          Yes to both. Same oil with new mercury filter.

          Where would I locate the pressure switch and sending unit on a 5.0 MPI? I think the sending unit is on top by the distributer, but not sure about the pressure relief valve. I'm guessing I plug a gauge into the spot where the sending unit is?
          2002 Bayliner Capri Sport 195 Mercruiser 5.0L Alpha I Gen II

          Comment


            #6
            I am not very familiar with that engine but I would check out the website below and see if it gets you to the right place. Once you find it you can remove it and screw the external gauge in, that is how I would go about it.

            I THINK this is your engine but I am not a marine expert:

            http://boatinfo.no/lib/mercruiser/ma...iser24.html#/0

            Wiring for Senders:

            http://boatinfo.no/lib/mercruiser/ma...er24.html#/370

            I also noticed a little note in the manual that stated: The best way to test the sender is to replace it with a new one. This made me chuckle at first but then it may make sense cause a new sender is probably cheaper than an external gauge if you don't already own one!

            On my 454, the oil pressure sender and low oil pressure switch are both on the lower aft port side of the block. Make sure you pull the sender and not the switch. The switch is used to trigger the low oil pressure alarm, at least that is all it does on mine.

            Comment


              #7
              I know this is a car and not a boat BUT the process is the same once you find your sending unit.

              https://www.google.com/search?q=chec...tf-8#kpvalbx=1

              Comment


                #8
                How awesome, I haven't heard any mention of Marvel Mystery Oil for years! - That was my grandfathers secret sauce.. basically any problem you had with your boat/car/motorcycle/lawnmower engine he would recommend adding that as a sure fire fix.
                1998 Bayliner 2858
                7.4L MPI / Bravo III
                Harbour Village Marina - Kenmore WA

                Comment


                  #9
                  What i would do ...

                  First remove the electrical connection at the sender clean real good, reinstall, maybe the problem is right there, run the boat, not fixed ?

                  Next remove the sender off the block, install a T with a manual gauge, most leave it there, now install the sender. Run the boat compare against the gauge at the helm. Say you still have the same condition.

                  Could be the fuel filter, yep could be.

                  Could be on your engine low voltage, yep that can cause all sorta gremlins, make sure your getting 14.5 steady volts at the battery while running. I MUST MAKE SURE YOU UNDERSTAND voltage on your engine mpi needs steady 14.5 volts while running.
                  Be good, be happy, for tomorrow is promised to no man !

                  1994 2452, 5.0l, Alpha gen. 2 drive. Sold ! Sold ! Sold !

                  '86 / 19' Citation cuddy, Merc. 3.0L / 140 hp 86' , stringer drive. Sold ! Sold ! Sold !

                  Manalapan N.J

                  Comment


                    #10
                    I like "Mystery Oil" if it does any good, I really don't know. But it does not hurt anything. Change your sender...a few bucks...clean the electrical connection NO tape on the threads. Be happy
                    Vic Stewart SN
                    Past Commander
                    Cape Fear Power Squadron
                    Ft Myers Power Squadron
                    1998 2859 7.4 L/B2
                    Raw water cooled

                    Comment


                      #11
                      "Chief Alen" post=810599 wrote:
                      What i would do ...

                      First remove the electrical connection at the sender clean real good, reinstall, maybe the problem is right there, run the boat, not fixed ?

                      Next remove the sender off the block, install a T with a manual gauge, most leave it there, now install the sender. Run the boat compare against the gauge at the helm. Say you still have the same condition.

                      Could be the fuel filter, yep could be.

                      Could be on your engine low voltage, yep that can cause all sorta gremlins, make sure your getting 14.5 steady volts at the battery while running. I MUST MAKE SURE YOU UNDERSTAND voltage on your engine mpi needs steady 14.5 volts while running.
                      Volts SHOULD be ok with two one year old optimas. New fuel filter. I'm going to replace the sender as soon as this rain settles down and report back.
                      2002 Bayliner Capri Sport 195 Mercruiser 5.0L Alpha I Gen II

                      Comment


                        #12
                        Ok...have a new oil pressure sender and got the old one off (that's tough to get at).

                        Do I use tape on the threads or not? Some say yes and others say no. The guy at the ship store said to use tape on the threads.
                        2002 Bayliner Capri Sport 195 Mercruiser 5.0L Alpha I Gen II

                        Comment


                          #13
                          Some people say no to the tape due to possible plugging of the hole in the sending unit. I say tape it , being cautious and judicious in the application,
                          -Boatless-

                          Bryers Cottage Marina
                          Harrison Twp, MI

                          Comment


                            #14
                            I did not tape mine as it was not called for in the instructions. I've also read a few stories where the tape may cause issues with the sender grounding properly to the block. I have no idea if this is an old wives tale or truth but I have had mine installed for a couple months now with no leaks.

                            Hope this solves your issue!

                            Comment


                              #15
                              If your sender has only ONE terminal....DO NOT use tape The sending unit threads are using the block for ground

                              If your sender has TWO terminals....tape is optional
                              Vic Stewart SN
                              Past Commander
                              Cape Fear Power Squadron
                              Ft Myers Power Squadron
                              1998 2859 7.4 L/B2
                              Raw water cooled

                              Comment

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