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F115 making black oil

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  • F115 making black oil

    This is my first post to this forum, so I'm sure if it's not in the right place, the administrators will straighten me out.

    I have a 2004 F115 Yamaha. It has a few hundred hours on it but I'm not sure how many exactly. Recently, I had it serviced at a Yamaha dealer for fuel injector issues (1 was clogged). They checked my oil during this service and the technician said it was like "fountain of oil" spewing out of the dip stick hole. The oil was black and and gassy smelling. He checked the fuel pump and said the pump was good. He cleaned the injectors, did a full maintenance (oil, plugs, etc.) and told me to keep an eye on my oil level. I have run the boat about 8 hrs after that service and I have noticed the oil levels rising again, and the oil is black already. Anyone with suggestions on what's causing this?


  • #2
    Did the mechanic offer any suggestions?

    How is the motor used? Is it idled a lot or run at low power? Is the water where you boat colder than usual?

    Was a leak down test performed to see if perhaps the rings are not sealing as they should? Perhaps a decarboning treatment is needed using YIEC.

    Has the thermostat been inspected to verify that it is working properly and not stuck open? Your model came with what is a 68V thermostat. Later model F115's were delivered with a 60V thermostat that causes the motor to run warmer. You may want to install the 60V thermostat. This may help with the phenomenon where the oil gets diluted with gasoline.

    Now if you idle a bit and if the water is colder than usual you may need to be running the motor at high power for a bit of time each time you use it. This may help to clean carbon out of the cylinders and may help to evaporate any gasoline that has gotten into the oil supply.


    • #3
      Kinda sounds like combustion chamber carbon loosened up and get down there (some how) and blackening up the oil so quickly..

      I had the link from Rodbolt (lost it some how) about a Yamaha commercial grade, dealer only product that'll clean up the top end, un-stick rings etc.

      Its soaks for awhile, run the engine, then change oil again.

      Rodbolt should chime in and POST back what that product was. I think there were TWO DIFFERENT products. I did find both available to the public I think on the Yamaha site (or maybe Flea bay).

      Found one:

      But there another, about $50 a quart
      Last edited by TownsendsFJR1300; 09-04-2016, 06:39 AM.
      1997 Angler 204 CC, 2006 F150 TXR


      • #4
        The mechanic's first response to this was to check mechanical fuel pump. He said it was good and not leaking. Before I even left the shop after them running the motor with fresh oil, you could see "black specs" in the fresh oil. It makes me think carbon when I look at it on my finger tip.

        I do run the motor around 5500 RPM when on open water, which is most of the time, at Kerr Lake, if you know where that is. I live in NC, so in the summer it is never cool. Maybe a decarboning treatment is the answer. The motor runs smooth, so it doesn't make me think the rings are bad. Although they could be. Thanks for your thoughts and any more advice you could give me.


        • #5
          Re-reading your first post, you said an injector was clogged.

          "Clogged", in my mind, is, it isn't injecting fuel efficiently, (if at all).

          My thoughts (for its worth).

          It is VERY possible, that injector was stuck open, allowing fuel to dribble into the combustion chamber, past the rings and "MAKE OIL", (THUS THE SUPER HIGH OIL LEVEL that smells like fuel)...

          I know you can clean injectors at home (look at you tube), but if one or two aren't sealing shut fully, that would explain the oil level rising, black oil (the fuel is cleaning the combustion chamber and slowly running back into the engine oil.)

          From what's been posted so far, IMO, you may want to inquire as to how he tested them, etc.

          Sending them out for a professional cleaning and testing may very well be worth your while..

          Unless he missed something in the fuel pump and that's leaking(the oil would obviously smell like fuel, but the black, assuming its carbon, leaning towards the injectors)...

          I'm not sure if you can see the tops of the pistons with the plugs out, but it can't hurt to peek (and look at the plugs for one ANY different) than the others.....
          1997 Angler 204 CC, 2006 F150 TXR


          • #6
            leak down would tell if it has carbon stuck rings.

            pulling stats and inspecting/testing would rule those out

            If not trolling a lot with that motor I would be looking at the two above


            • #7
              Both of my 2006 Yamaha F150s were "making oil". Here's the link to the thread which explains how I fixed the immediate issue. I do a lot of drift fishing at idle, so the thermostats can stay closed for long periods of time while the engines are running. Making oil will be a recurring issue with my engines if I don't stay on top of it.



              • #8
                over propping is about the leading cause of making oil,followed by overcooling then injector leaks and fuel pump diaphrams.
                that motor MUST be capeable of 5800 RPM with THAT days load.
                ya cant prop it with 1 person and 1/2 tank of fuel then add 9 ppl and a tube.