Re: Water in lower unit oil
Bad news... can cause corrosion in the gearbox. Good thing you found it and are going to fix it.
Most outboards have 3 places where water can enter the gearbox...
-At the prop shaft
-At the drive shaft
-At the shift rod
Each of these places has either one or two oil seals. You have a bad seal somewhere.
Drop the lower unit and drain it by removing both of the oil drain screws. Then replace one of the screws and put a pump with pressurized air into the other hole. The pump should have a pressure gauge on it. Fill the gearbox with pressurized air and you may be lucky enough to simply hear the air leaking from one of the three aforementioned locations.
If you do not, it could be a very small, slow leak. In that case, spray soapy water on each location and look for bubbles.
You will likely then find which seal is leaking. Replace the faulty seal/s and refill the gearbox with pressurized air. Check your manual to see how much pressure it should hold, and make sure it holds it. If it doesn't, you may have another faulty oil seal in one of the other of the three locations.
Once you've gotten the LU to hold the correct amount of pressure, fill it with oil and replace it onto the outboard.
You can see videos on youtube of people doing this very thing.
The oil seals for each location are not always interchangeable, so make sure you buy the right ones. Also, very important, make sure you face them the right way. I believe with Mercs one faces in and the other faces out. On Yamaha's, they both face in. Merc tries to keep the oil in and the water out. Yamaha's theory is that it is far more important to keep the water out. Pressure in the Yamaha gearcase is therefore higher than in a Merc.
Before installing the new oil seal/s, smear marine grease around their perimeter. Also, you'll need a tube of the right diameter to use as a tool to hammer them into place. Sections of appropriate diameter PVC pipes often work well for this. You don't need to buy a special tool.
Just some background info so you understand the concepts.
