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Excessive oil consumption 115 HP Mercury

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  • Excessive oil consumption 115 HP Mercury

    I have recently purchased a 1998 Mercury 115 HP 2 stroke outboard with about 150 hours on the engine. The engine consistently uses too much oil, about 40 to 1 ratio. I have adjusted the linkage for the carburetors and the linkage for the oil pump on the engine to recommended specs. Also after each use and the engine is tilted up when at the dock, there is an oil leak from the front of the engine. I don't know if this is related to the excessive oil consumption or not. Does anyone have any ideas where to look?

  • #2
    Re: Excessive oil consumption 115 HP Mercury

    Comments deleted. My comments applied to a different size motor.
    Last edited by hkeiner; June 5th, 2009, 10:17 PM.
    1996 Mercury 150HP V6 carbed outboard motor and Maxum 1900XR bowrider boat


    • #3
      Re: Excessive oil consumption 115 HP Mercury

      That system is gravity fed and has no remote tank and I have replaced 3 customer tanks this year for such leaks. All 3 had cracks in bottom where oil level sensor is installed.
      Attached Files
      When in doubt,Trim it out!!!
      Business Owner & Certifed Technician
      Boats I own & use
      20ft Javlin w/250 Junkrude
      17ft Bullet w/200 Merc (SOLD!!)
      13ft Allison w/150 I-6
      17ft Hydra-Sport 175GT
      15ft Allison w/75 Stinger(project)
      14 x 48 Drifter with 1100SS Merc


      • #4
        Re: Excessive oil consumption 115 HP Mercury

        I realize this thread has not been active for a few months, but I have the exact same issue with my 115hp Offshore 1997 model. Some background the motor uses an excessive amount of oil, on a good day about 27:1 ratio, that is about 3 quarts oil to 20 gallons of gas. Motor does not smoke at all, except under cold starts. I only take her out once a month so with standing I figured smoking from cold for a few seconds was normal. Once she is warmed up no smoke at all. Compression is good no more than 5% variance across all 4 cylinders, new plugs and no fouling after 4 runs on the river.
        Also when trailering the boat and tilting the motor all the way up after a day or so clean oil starts to leak out the front of the hood. I have traced the oil back to what appears to be an injector type tip in the bottom most carb. The motor is an inline 4 cylinder engine, the top 3 carbs show traces of oil starting to leak out through throat but the bottom one spews it out. I can sit and watch as the oil slowly bubbles out under what appears to be gravity, all this is while the motor is not running. I did find the air box was missing a gasket which seals the lower 1/3 of the air box and when fitted keeps the oil inside the airbox. So no more leaking out while tilted, however this does not solve the excessive use issue. Also with me installing the gasket I could have added to my smoking when starting cold problem as now the oil has no were to go and must be burnt off at start.

        Question I have is the oil flow adjustable, anyone know how. I plan to get myself a manual tonight and do more investigation. Any additional information will help.


        • #5
          Re: Excessive oil consumption 115 HP Mercury

          I have the same issue, '95 125 2 stroke. I removed the oil injection just by personel preference and capped the oil intake tube. The tank is gone so no oil leak there. Mixed gas in the tank. With the air box removed, I see oil drooling out of all 4 carbs. All are about the same, coming out of the small spout in the bottom of all carbs. My concern is, is the oil "de-mixing" in the bowls? It's not a huge problem, I keep a roll of paper towels in the boat but it does get tiring to see blue-green oil in the back deck of a white boat not to mention oil in the water. I don't know how we would go about fixing this issue. I have rebuilt all carbs with new gaskets with no luck. Just adding my information.
          1995 SeaRay Laguna 18 Mercury 125


          • #6
            Re: Excessive oil consumption 115 HP Mercury

            Just an update, I picked up the manual for my motor today. Gonna try and get some quality time in tonight to start analizing the oil injection system, hopefully the answer is staring me right in the face but that I doubt. I will post more on progress.


            • #7
              Re: Excessive oil consumption 115 HP Mercury

              Hello everyone,
              Just finishing a major rebuild on my 1990 115 mariner. Wow! was this a treat! I have learned several things about this oil injection system some good and mostly bad. I also have had the oil leak problem that you speak of but I never could pin point where it was coming from. I ended up replacing all of the hoses from the resevior to the injector and from there to the fuel pump. It seems to be fixed but I havent had it out to open it up. I did find that all of the hoses were very hard and broke in half when bent.


              • #8
                Re: Excessive oil consumption 115 HP Mercury

                All oil hoses should be replaced every 5 years. If one breaks or cracks, catastrphic engine failure follows quickly. A wise $2.00 investment.
                1970 14ft Winner w/ a 1988 90hp Merc (47 seasons of saltwater operation);
                2003 Malibu skiboat V-8 inboard. (fresh water boat)
                Original owner of both.
                First boat; 1963 13ft Fabuglass Fury 50hp Merc (63-69)


                • #9
                  Re: Excessive oil consumption 115 HP Mercury

                  One common aspect of several of these threads is the fact that the leak occurs when the motor is trimmed up on the trailer. First, is it oil or a mix of oil and fuel? When you tilt your motor up to install your transom saver or to lock in your trailer bracket the top carb swings in a very large arc and is almost horizontal causing all the fuel to dump out the bowl and run down the front of the cowling until it eventually leaks out the bottom of the engine cowl. Second, if the enigne has the original Tygon lines, they need to be replaced. Changes in oil additives make the old lines stiff and brittle so they crack with just a slight touch. As far as oil consumption goes, it is nearly impossible without doing the proper measured and metered flow reading to determine if an enigne is running at 40:1 or at 50:1. The cam on your oil pump changes the flow rate at idle to higher rpm's so the flow and mix vary at idle and then goes to full mix off idle.


                  • #10
                    Re: Excessive oil consumption 115 HP Mercury

                    Back again, and thanks to all for the good comments. So I got myself a service manual boy what a treat, being mechanical in nature, the book is very detailed in its explainations of setting the fuel air mixtures, idle and most of all in my case the oil pump.
                    I have not begun the setting procedure as it will take some time and I would like to do it over the weekend. I did do a quick inspection of the oil pump calibration and guess what its way off, the two timing marks are about 3mm apart on the rich side. I will not mess with them yet till I go through all of the setup as described in the book.
                    I did have a question for all the engine guru's out there, the book mentions an "idle speed screw" and an "idle stop screw" are these one and the same? They do not provide illustration for these unfortunately, I am assuming the idle stop screw is the one close to the throttle cable on the throttle arm. I would assume the idle speed screw would be some where in the carb region, otherside the roller cam?
                    tskm2001 - at first I thought it was raw oil leaking out of the front, now at closer inspection I realize it could be mixed with fuel and the float bowl explanation makes a ton of sense. Thanks I will research further.


                    • #11
                      Re: Excessive oil consumption 115 HP Mercury

                      On second thoughts if anyone has a pic they can post clearly showing all the setting screws with descriptions maybe an exploded view, I would appreciate it.
                      Some of the screws i am looking at idles stop screw, idle speed idle, low rpm timing screw, WOT timing screw.


                      • #12
                        Re: Excessive oil consumption 115 HP Mercury

                        Here you go. Also check to see if your manual has a section on linkage adjustments. That's where this came from.
                        Attached Files

                        95 Procraft 180 combo F/S W/115 Mariner
                        90 Playcraft 24' pontoon W/88 Evinrude
                        02 F250 7.3 PS


                        • #13
                          Re: Excessive oil consumption 115 HP Mercury

                          Originally posted by trackerdanbass1 View Post
                          Hello everyone,
                          Just finishing a major rebuild on my 1990 115 mariner. Wow! was this a treat! I have learned several things about this oil injection system some good and mostly bad.
                          I'd be interested to know what the good and bad things about the oil injection system are that you learned about.

                          Thanks !!


                          • #14
                            Re: Excessive oil consumption 115 HP Mercury

                            Thanks The_Kid that helped a ton. Well here is the update spent the whole day doing the link and sync, timing adjustment, idle setting, cam and follower, oil pump you name it I did it. All thats left now is to adjust the top 2 carbs air/fuel mix tomorrow when I hit the water.
                            Pros of doing this procedure, I realized things go way out of whak over the years. The timing for idle speed was about 8 out and the WOT timing was 18 out, she was running at 40BTDC at WOT. I am expecting better performance from the old girl tomorrow. Everything went well, except for the air /fuel mix which needs to be done in forward gear at idle. When I was done I hooked up the water hose and decided not to give her any throttle on the start. In the past I had to give her full throttle from a cold start, this time first crank she took and died, second crank fired up and ran smooth as silk. I was real impressed.
                            Cons of doing this, you have to keep your wits about you at all times, know your parts and where they are located. The last con is something I will need to do more research on, my throttle cable is set correctly with just enough preload. At idle the cam and follower have the correct gap, the carbs are all closed but for some reason I run out of throttle travel when accelerating. Its not much but when I bottom out on the cable retainer I have about 1 or 2mm of carb plate movement still to go. The only way I can see this improving is if I reduce the cam and follower gap, but the spec is only 0.125mm to .57mm and I am at 0.3mm at the moment. I am not sure how much this will effct performance as I mentioned the carb plates are only about 1 or 2mm from perfectly horizontal.
                            I will post again after tomorrows river run, interrested to see my oil consumption after the oil pump adjustment.


                            • #15
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                              Re: Excessive oil consumption 115 HP Mercury

                              Probably my final update, went out Sunday morning. Water was clam and after the launch she started right up, i am very happy these days with the start up. I spent the first 20 minutes idling around the creek, had to warm the motor up before adjusting the air/fuel. Once that was done she ran smooth, idle speed at around 700rpm, time to gun it.
                              Headed out the creek into the river and slammed her down, the hole shot was much improved no more bogging down, top speed was slightly reduced but only by 1 mph. WOT rpm was around 5000rpm so right in the sweet spot, no need to change the prop.
                              Oil consumption has definately improved enormously, all in all I claim success over my problem. Thanks again to all for the comments.