oldslowandugly
Petty Officer 3rd Class
- Joined
- May 12, 2010
- Messages
- 98
There are a lot of water-in-the-oil threads so I just thought I would throw this out there. Any water means a seal is leaking, and it can be as easy as an oil fill plug seal or as hard as a prop shaft seal. The key is finding which ones are leaking. When I rebuild a lower unit, I test it for both positive and negative pressure, as per the factory manual. I originally made this little tester tool to use on my old '56 30hp with a bicycle pump w/gauge and a Mighty Vac tool. All it is is a brass tire tube valve stem inserted into a short piece of plastic tubing and secured with a hose clamp. I force threaded it so that the tubing screws into the oil fill hole. I use the bicycle pump w/gauge to test positive pressure and I test for up to 20 psi. I unscrew the valve from inside the stem and hook up the Mighty Vac with a short piece of hose to test for negative pressure up to 20 hg. A leak will make noise, and soapy water will bubble as a give away. If your lower unit can hold both negative and positive pressure for 15 minutes, you can be sure it will not lose any oil or take in any water. Just click on the pic for a better look. 
