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  1. #1
    Cadet
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    Default yamaha 115 4-stroke gas in the oil

    I have a 2007 yamaha 115 4-stroke that is getting gas in the oil. The motor runs great and you would never know it was getting gas in the oil if you did not check the dipstick. I have ran carbon break down chemicals through the gas, I have ran seafoam through the crank case as well as through the gas while at the same time squirting a carbon reduction chemical through the intake. This has all been done several times. But still getting gas in the oil. Compression is good, again motor runs great. Any advice please.

  2. #2
    Vice Admiral
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    Default Re: yamaha 115 4-stroke gas in the oil

    Frequent reasons for making oil

    leak in fuel pump,
    stat stuck open causing motor to run too cold
    over propped and lugging motor
    Idling / trolling too much and not getting motor up in temp

  3. #3
    Commander
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    Default Re: yamaha 115 4-stroke gas in the oil

    The #1 reason for this as 99yam40 has mentioned is the engine isn't coming up to operating temp. If the engine fails to reach operating temp, it doesn't burn the fuel completely and it gets past the rings and into the oil. Doubtful if the fuel pump is at fault for two reasons. The engine would starve for fuel at higher rpms and the pump would make a tapping noise like a valve out of adjustment. It takes fuel pressure inside the pump to keep the plunger riding on the cam without slapping it.

  4. #4
    Cadet
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    Default Re: yamaha 115 4-stroke gas in the oil

    I replaced the fuel pump and the thermostat. Then shocked the motor again with chemicals I obtained from marine store, ran the motor rather hard on two occasions with very little idling and the dip stick level moved from middle of stick (where it is suppose to be) to top of cross-line level mark. Again the motor runs great, you would never know there was a problem without monitoring the level change on the dip stick.

  5. #5
    Commander
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    Default Re: yamaha 115 4-stroke gas in the oil

    What is the max rpms the engine will turn?

  6. #6
    Cadet
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    Default Re: yamaha 115 4-stroke gas in the oil

    I am not exactly sure what the engine will turn up, I do not have a tack on the boat, but again, the engine runs excellent. At trim and throttled up it will nearly scare you. There is no problem with performance, compression, smoking, etc. Simply, after any running time it accumulates gas in the oil. Is there a sensor similar to what is on a car, i.e. cold start sensor that tells the computer to dump gas until the engine heats up? Maybe some sort of sensor that dumps more fuel than needed and that extra fuel is not burning off. Not to sound redundant, but you would never know there is any problem, performance is excellent, but for, checking the dip stick. For example, after the last chemical shock in an attempt to rid the engine of any carbon build up, I changed the oil, placed the measurement at exactly mid-point on the dip stick; ran the engine for less than an hour, allowed for wait time, ran it again the following day, stop and start with little idle for a couple of hours, check the dip stick and the oil/gas capacity moved up the dip stick to the upper cross-lines. (Suggesting about a 1/2 quart of gas accumulation). Same result as the last time.

  7. #7
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    Default Re: yamaha 115 4-stroke gas in the oil

    Cold start advances the timing for starting so that wouldn't be the problem. You need to perform a leak down test to see if might have more blowby on one cylinder more than another. Also you might have an injector leaking and not closing off after firing.

  8. #8
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    Default Re: yamaha 115 4-stroke gas in the oil

    Thank you very much, I will try that and get back to you. That sounds probable. I will let you know the result. Assuming, that corrects my problem, if you get around the coast of Mississippi, I will have to take you fishing.

  9. #9
    Supreme Mariner Silvertip's Avatar
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    Default Re: yamaha 115 4-stroke gas in the oil

    A leaky fuel pressure regulator will dump excess fuel into the engine. As was mentioned, a prop with too much pitch causes lugging where the throttle must be open too far for the amount of work being done. This again results in excess fuel being put into the engine. Last question: Is this engine new to you or have you owned it for awhile and this problem just surfaced?

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