Oil Slick from 15hp Merc

[electricsailor]

I just acquired a boat with a 1996 15hp merc. I noticed a slight oil or fuel/oil slick bubbling up from the lower unit after stopping the motor. In the barrel it seems to rise after idling a while at operating temp and looks a little thicker. At first it's just a sheen. No leaks on driveway when motor is stopped, though. Is this a matter of concern. Where should I look first?

 

[dean carpenter]

Re: Oil Slick from 15hp Merc

just acquiring the motor would mean that it may have been sitting for awhile. did you change the lower gear oil? possible it may have some water in it from bad seals. run a plastic hose from the top drain plug into a glass jar to check for the water. does this happen while running it in gear? have you ran this in the water yet or off the ear muffs in the driveway?

 

[diaric]

Re: Oil Slick from 15hp Merc

i've got the same trouble with my old merc on idle when trolling. i know its time for a carb rebuild on this one, and i think its running a touch rich on idle.

 

[electricsailor]

Re: Oil Slick from 15hp Merc

The motor was run by the previous owner a lot last year but I did not run it until this past weekend. Actually this oil slick showed up after running it around for a day or two. I have not changed or checked the gear oil in the lower unit yet. The slick initially is a light sheen that comes up in small drops until a few minutes after shut down. It looks like fuel but I can't be sure. It may be gear oil. Is there a way to tell the difference?

 

[diaric]

Re: Oil Slick from 15hp Merc

your odds are high its fuel. if your loosing gear oil, it is unlikely to appear as a slick on top of water. also, if your loosing gear oil, your gaining water in the lube. give the lube a check, if its not milky from water intrusion, your not loosing any

 

[Yepblaze]

Re: Oil Slick from 15hp Merc

All 2 stroke motors run in a barrel emit oily goo.

 

[electricsailor]

Re: Oil Slick from 15hp Merc

If it's fuel and appears to be coming from under water when not in a barrel, then what is the likely source? The exhaust vents from above the water line. However if the exhaust port is ubstructed, I see exhaust bubbling out from below the cavitation plate.

 

[Harker]

Re: Oil Slick from 15hp Merc

Unless it's a VERY old Merc, the exaust is scavenged out through the center of the prop. The holes up towards the powerhead are "carb relief" holes so the motor doesn't overload.

 

[Scaaty]

Re: Oil Slick from 15hp Merc

ALL 2 cycle motors will leave a slick in a barrel..your fine