CONTINUOUSWAVE

While draining the gear lube on my 2006 Mercury 75-Optimax Serial 1B318814, before any oily came out a couple of ounces of water came out [from the gear case drain-fill] . [The gear case lubricant] had a brownish milky look.



I inspected the propeller [shaft] bearing seals and drain-fill screw seals; all seals looked good.

I also replaced the water pump gaskets and impeller.

I suspect that last season I only filled the gear lube to the Oil Level port and didn't fill all the way to the vent hole.

Q1: Is there a chance that [the under-filled lubricant level is the cause] for water [in the lubricant]?

Q2: Should I bother putting new gear oil in and just roll the dice this season?

Q3: What could go wrong?

I may only put on 15 to 20 hours on the engine in 2021.

I would pressure test the lower unit. If it holds pressure you can refill oil. Be sure to use new sealing washers on both the upper (vent) and lower (drain) plugs.

ASIDE: I bought a used outboard that had water in the gear lube. I replaced the seals under the water pump and that fixed the water-in-lubricant problem.

Thanks MarkCz.

I changed the oil and gaskets. [The gear case] seem to be holding [the new lubricant]. I will inspect mid-season of 2021.

The lubricant as seen in Figure 1 certainly has the appearance of being mixed with water.