Announcement

Collapse
No announcement yet.

Preferred Oil for the Mercruiser 7.4L MPI?

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

    Preferred Oil for the Mercruiser 7.4L MPI?

    I'm doing my first DIY oil change. I was wondering if there is consensus on what oil should be used. It seems most blogs favor Mercruiser oil. But I see various opinions on synthetic vs. non synthetic, and 20-40W vs. 25-40W. I'm told for the synthetic the spec needs to be NMMA FC-W. There is even some controversy on what the oil capacity is- 6 to 8 qts.- but "go by the dipstick" seems to be the safest approach. My Mercruiser 454 MPI is pushing a Bravo 3, in a 2000 Ciera Sunbridge 2855. The engine has approximately 330 hours, mostly low-speed, as we prefer to burn ~5 GPH vs. 20! Thoughts?
    Jeff Prime
    "Optimystic Prime"
    2000 Bayliner 2855 Ciera Sunbridge
    Anacortes, WA

    #2
    I've used Rotella 15-40 for years. I'm in the water for about 5 months a year and do 50-100 hours a year and change it at the end of the season. As it's relatively low hours I've never seen the need for synthetic.
    Doug
    Hanging Loose
    98 Carver 350 Mariner
    2013-
    KRUSTY KRAB
    2001 305
    5.7 BII
    2006-2013

    Comment


      #3
      I had better experience with maintaining oil pressure when I slowed to an idle after cruising at 32-3600 rpms when I used the merc oil.
      P/C Pete
      Edmonds Yacht Club (Commodore 1993)
      1988 3818 "GLAUBEN”
      Hino EH700 175 Onan MDKD Genset
      MMSI 367770440

      Comment


        #4
        Merc/Quicksilver 25W40 is what I have used for years.
        1997 Maxum 2400 SCR 5.7LX Bravo II

        Mike

        Comment


          #5
          I use delo 400 SDE 15W-40 mostly because I can get it for half the cost of the Mercruiser stuff.
          Dave
          Edmonds, WA
          "THE FIX"
          '93 2556
          Carbureted 383 Vortec-Bravo II 2.0:1 18 1/4x19 P

          The rebuild of my 2556 https://www.baylinerownersclub.org/f...76?view=thread
          Misc. projects thread
          https://www.baylinerownersclub.org/f...56-gctid789773

          Comment


            #6
            I believe that the 15w-40 diesel oils still have the zinc additive ZDDP, which is a antiwear additive that protects things such a cam to lifter wear. Might read up on that.
            2550 Cierra, AQ260 Volvo Penta (350 Chevy)
            Laporte, CO

            Comment


              #7
              For the older flat tappet motors the mercruiser 25w40 is not the best choice as it does not have the zddp additives. 15w40 amsoil sunthetic is a good choice as are most of the diesel oils. For marine use you do want to have an oil with the rust protection additives also. Sonething that regular diesel oil does not have. The 15w40 amsoil is a diesel and marine oil has everything your looking for and amsoil is one of the top oils on the market today for shear strength.

              I dont know if the 2000 7.4l is a full roller top end or not. In my case (1995) it is a flat tappet cam.
              Doug
              1995 2859 -extensively rebuilt/restored 2016/17
              496 big block - Bravo ll leg
              The Doghouse
              Prince George BC

              Comment


                #8
                Fresh annual oil!
                Tally and Vicki
                "Wickus" Meridian 341
                MMSI 338014939

                Comment


                  #9
                  Look up some virgin oil analyses of different oils, I think you'll find that even the 15w/40 does not have much more zddp than the Merc oil does, all this was changed a few years back. That said, with an engine with roller tappets it does not matter. I am not sure when the small block V8s went to the roller tappets but the 4.3 for sure had them as long ago as 1987, my '88 has one for sure. When I did the top engine overhaul (reman heads and new headgaskets) I pulled out all the roller tappets and the cam lobes and the rollers looked like new. All original 1988 stuff. I ran the engine on Delo straight 30 and 40 about the 1st 10 years then changed to the Merc oil and found my oil pressure readings, consumption etc to be about the same. The older Delo straight weight did have more zinc but that has changed. My Delo results from 2011 had 1705 ppm of zinc and the Merc results from 2015 had 960 ppm of zinc. I've been looking around for a virgin oil analysis of the Delo 15w/40 and what I've seen suggests that the zinc is at about 1200 ppm. Maybe it matters maybe it doesn't. The Shell Rotella and Delo can both be bought for less than the Merc. One thing though, for salt water boaters I can say that the corrosion resistance of the Merc oil is good. I had 2 blown HGs and salt water in the engine for a week or so (but had drained the water out as soon as I could and fogged the cyls). When I took it all apart, very little corrosion, none on the valve train, pushrods, lifters, cam lobes, etc. Just a thought if you run in salt and your boat lives in the water.
                  88 Four Winns 200 Horizon 4.3 OMC
                  98 Jeep Grand Cherokee 4.0/Selectrac
                  07 Jeep Grand Cherokee 5.7 Hemi/Quadradrive II

                  Long Island Sound Region

                  Comment


                    #10
                    Amsoil synthetic is the way to go. And I change it every season.

                    Comment

                    Working...
                    X