What is this leaking from my lower unit?

l008com

Senior Chief Petty Officer
Joined
Jun 14, 2007
Messages
751
I unwrapped my boat today for the first time all year. The first thing I did was change the lower unit oil. I drained the old stuff out and put some brand new stuff in. I barely used the boat the last few years so the oil that came out was super clean. I filled up the new stuff and I'm on my way.

Then when I'm trying to start the engine, I notice something is dripping out. There's a little hole that I guess is some kind of vent hole? Except it's well below the water line so seems like that vent would become a water inlet? What is leaking out? Whatever is leaking out is filthy! Is there some OTHER kind of fluid/oil in the lower unit besides the primary gear oil?

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What do you think?

The motor is a 1989 Mercury 90HP 3-cylinder outboard.
For all it's flaws and age, with a new battery and a full tank of gas, it did start right up :) I didn't make it to the water yet though. Soon, hopefully.
 

Chris1956

Supreme Mariner
Joined
Mar 25, 2004
Messages
27,840
Smell the stuff. If it stinks like eggs, it is gear oil and not normal. If it smells like oil or gasoline, it is 2 cycle oil and normal.
 

l008com

Senior Chief Petty Officer
Joined
Jun 14, 2007
Messages
751
Smell the stuff. If it stinks like eggs, it is gear oil and not normal. If it smells like oil or gasoline, it is 2 cycle oil and normal.
Unfortunately I did not give it a whiff before I put the boat away.

But why would 2 cycle oil be coming out of a hole in the lower unit?

And if it's gear oil, how is it coming out dirty when I just put it in clean 10 minutes earlier? Not only that but the 'dirty' oil I removed wasn't even dirty either since it had so few hours on it. Yet the stuff coming out of this hole is way dirtier than all that.
 

racerone

Supreme Mariner
Joined
Dec 28, 2013
Messages
37,816
It is a drain hole for a cavity.----Prevents freezing / cracking.------Normal for a 2 stroke to leak some oil there.------I have said it many times.------The mixing of gas and oil and operation of a 2 stroke is not well understood.
 

airshot

Vice Admiral
Joined
Jul 22, 2008
Messages
5,080
Oil in the fuel causes the exhaust to contain a black residue, anything that is part of or connected to the exhaust will have that black residue. That hole may be a drain opening for the leg exhaust, thus the black crud
 

jimmbo

Supreme Mariner
Joined
May 24, 2004
Messages
13,446
Even Gear Oil can pick up Contaminates that it comes into contact with. Use you Nose to give you an Idea, or better yet, do, or get someone to do, a Vacuum-Pressure Test on the gearcase
 
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