mercury 115 4 stroke efi "making oil"

DarcyDarcy Posts: 1,711 Captain
Just thought id share.

My "new to me" Mercury 2006 115 4 stroke efi has been making a little oil. In the 6 months since the last oil change, the level has slowly gone up about a 1/2" on the dipstick, smells a bit like gas and was black. So ive been reading about this situation in past threads and other sites, and a lot of the info was pointing at the thermostat being stuck open or faulty. So last week i decided to change it. It was not stuck open, but the rubber seal ring was in pretty bad shape. Very flat(compressed) and cracked. Put the new one in and took the boat for a spin. Ran her hard WOT for a good 1/2 hour (which i normally do on the way back in). To my surprise the oil had gone back down the 1/2", to about the 3/4 mark of the dipstick guage (where i filled it to roughly, 6 months ago). And i did tilt it up first to drain that extra oil out before checking it. No longer smelled like gas and the color was better too. Not golden but not black. Right about where it should be for 6 months. I'm wondering if that bad rubber seal ring was letting water bypass the thermostat, making the motor run too cold. I did test the thermostat and it still opened and closed at the correct temp.
Also could that 30 min WOT (with the new thermostat) really burn off that much gas from the oil. WOW.!!!

This might be good info for anyone else having this problem.
"No i'm NOT Darcizzle!":blowkiss


  • Pat LPat L Posts: 440 Officer
    I guess its possible it could leak by the seal, but if its working now I say leave it. Just keep a check on the oil level. I would change the oil and filter tho just as a precaution from having the gas in it.
  • Oldfox1939Oldfox1939 Posts: 521 Officer
    If water was getting in the oil, it would be milky.

    My guess is you are getting gas in the oil, you probably cooked it off by running it hard.

    You should check to see if you are rich on the fuel.
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