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Merc 115 2007 small oil leak - guidance requested


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Good Day, 

It appears there is a small amount of oil collecting on and then dripping from one of the lower unit mounting screws. Several drops run off only when the motor is tilted up out of the water. There is no leak when motor position is down, either off or running at idle. I am not sure at this point if it is gear or motor oil. The oil seems to be rather thin as it drips quickly, then stops after a few minutes. I did not have a 15mm wench at the time to try to tighten the lower unit bolts, hoping they just worked themselves loose. 

 

Any ideas on what else I should look for?

 

Appreciate any feedback. I am away from the boat currently, but will be addressing the issue next week.

 

Dave

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You didn't mention whether IO or outboard but sounds like outboard  so a couple things come to mind: One is there is usually a small gasket seal around each of the drain screws on the lower unit. If the little gasket is missing, water can get in and fluid can leak out. Two is your lower unit seals may be compromised and water may be getting in and displacing the fluid out the drain screw hole. Unscrew the lower drain screw and see what comes out  if water or murky fluid may be bad seal.

Edited by Sk8man
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You didn't mention whether IO or outboard but sounds like outboard  so a couple things come to mind: One is there is usually a small gasket seal around each of the drain screws on the lower unit. If the little gasket is missing, water can get in and fluid can leak out. Two is your lower unit seals may be compromised and water may be getting in and displacing the fluid out the drain screw hole. Unscrew the lower drain screw and see what comes out  if water or murky fluid may be bad seal.

Thanks Len, yes outboard. Looks like it is gathering around the mounting bolt between the lower unit and the engine. There are two on either side and the starboard top bolt/nut is we’re the drip is originating ( from first look). Hoping just worked loose from a bottom scrape or 100 hours of trolling. I did not have a wrench to torque it down to test. I will verify the fluid as well , as you suggest.


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  • 3 weeks later...

Les, I am thinking your first option above may be the cause. I have not had a chance to drain the lower unit to verify milky oil, but, I did find a loose vent hole screw. I was able to turn it tighter by about 1/8 of a turn. I am thinking water may have gotten in. It would make sense that if water got in the lower unit vent hole, the oil would float to the top, then out the drain hole when tilted up. It seems to drip more oil after the motor is sitting in the up position over night. 

 

Dave

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On mine it turned out to be that the drain screw washers (that seal the screws)  were compromised and some water had gotten in. When the lower unit was pressure tested it was OK so new lower unit fluid added and it was good to go although I took the opportunity to have a new impeller/pump installed.

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Les, 

I am just getting back to the boat to work on this. More info:

1) Gear oil is coming out the port side drain hole, upon tilting motor down. Small drips

2) The amount seems to increase after motor sits overnight or for a few days

3) When vertical in water a very small amount of oil seems to bubble up. One small bubble every few seconds, then stops. 

4) No oil appears to be coming out when running at idle

5) The front "vent" screw was loose about  1/8th of a turn. I tightened. Manuals call this the drain screw as well, though utilized only to receive the pressure when filling.

 

If water had gotten in the vent/drain screw because it was loose,

1) Would this be the possible issue? 

2) Is the drain hole above or below any of the internal engine seals?

3) I am thinking if the drain hole is part of the lower unit, then what I am seeing is just the displacement of the oil with the water that had gotten in before I tightened the vent screw. Meaning no new water is going in the lower unit and just changing the oil would be the fix. If the drain hole is above the seals and not part of the lower unit, then oil must be floating in water and after sitting for a bit, comes to the top and when the engine is tilted, coming out the drain hole. 

4) I have probably tilted the motor up and down 20 times by now and still seeing oil drip out through the port side drain hole. 

 

***updated

1-Pulled the drain plug for the lower unit, milky white grey with water in it

2- removed the two drain/vent plugs...one appears to have a deteriorated washer/seal, broke off in two parts when removed.The other was loosely fitted.

3- Will fill with new oil tomorrow and test at the ramp and see what happens

 

 

Thanks for any further thoughts,

 

Dave

 

 

 

 

 

 

 

 

Edited by superhawk18
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