Pressure Testing Lower Unit

[fishnowworknever]

So I installed an extension kit in my Mercury, all went well. Put new gear oil in. I started it up, let it idle for a while with the muffs on, turned it off and opened the drain/fill plugs and of course out comes milky colored gear oil.

I am going to try and pressure test it tonight to see if I can determine where it's coming from, other than the prop shaft and water pump gaskets where else could this thing be leaking? The prop shaft I wouldn't think that could be it since it was not submerged in water, just had the muffs on the inlet. My guess would be the water pump gasket(s) or the drive shaft oil seal....

Any other suggestions before I rip my hair out trying to find it?

Thanks

Info:

1972 Mercury 40hp 402

[boatfixer]

I'll bet the drive shaft seals just as you mentioned. Its the only place that would be pressureized while not in the water, short of a crack somewhere in the housing, though very unlikely.

[fishnowworknever]

Exactly what it was. Sprayed soap+water all over the water pump under 10psi..bubbles everywhere in about 2 minutes.

[boatfixer]

Good to hear you found it!