2002 25hp Mercury lower unit

Took my boat out the other day and noticed some water in my lower unit. Checked the easy fix and replaced the seals on the drain and vent screws, but took it out today and had the same thing. Figure the next step is the prop shaft seals ? Any thoughts on this ? I've attached a picture of what the oil looked like when I drained it

What I did to remove the guesswork was to create a pressure tester with a bicycle pump and the fitting from the gear case fill pump. I then removed and drained the lower unit and used my homemade pressure tester to find where it was leaking. Just submerge the lower unit and add a little pressure and it becomes obvious. In my case it was the prop shaft seals. I was able to replace these seals without tearing into the lower unit.


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Awesome idea ^^^^ bookmarked

The key to the bicycle pump pressure tester was the valve stem from an bicycle inner tube and the plastic tube that came with the lower unit fill pump. Remove the valve stem ( by this I mean the rubber part that sticks out an inch and a half or so) from the bicycle tube, install it in the fill pump tube (couple small hose clamps) and you have a pressure tester.


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