Water in gear oil

[katch_me]

I would like your opinion on something. This is an early 80's Mercury 90 inline 6 cylinder. Ever since i have owned this boat (15 years) I have always seen very small amounts of water in the lower unit gear oil. When I say small, I would say less than 1oz of water. I know this because I used to change the oil at the beginning of the season. So over the winter the water will drop out to the bottom. Now I change at the end of the season, and it's milky.

10 years ago when the boat was at a shop getting work done I asked them to change the gaskets to fix this problem. I am not sure if they did because the problem never went away. And the plug and vent gaskets have been changed and checked a lot of times.

My questions would be if water is getting in why is the whole chamber not filling up with water? The volume doesn't increase or decrease. I feel like just leaving this problem as long as it doesn't get worse, unless it could be a simple repair. What do you think?

 

[Texasmark]

SWAG:
When filling, one inserts oil from below the gearbox and continues to fill till clear, solid, non-bubbly oil exits the vent just above the antiventilation plate. The upper drive shaft seals are beneath the water pump so there is some room for LU oil to expand at the top of that chamber. This set of seals, just below the water pump is one place water can enter.

Other places are the servicing screw seals you mentioned that have been regularly changed (so they should not be contributing to your current problem, and 2 more entrance places being the shift shaft seal at the front top of the LU and the prop shaft seals.

On a water entrance mechanism, the same thing that causes problems in trailer wheel bearings also can cause LU water to enter and that is for you to have a leaking seal and the LU (and/or wheel bearings) to be hotter than the water temperature when you launch, and with the leak, reduction in temperature creates a negative pressure which can suck in ambient water.

Also, when operating the boat on the water, the engine running heats up the LU oil which may not escape (for whatever reason) but does cause the oil to expand. When stopped, or when submerged, like when launching, or after running, the oil cools, thereby shrinking, thereby generating a negative atmospheric pressure and a mechanism for sucking in outside water.

 

[katch_me]

The vacuum pulling in small amounts of water makes more sense. I leave the boat in the water all year, so that heat must be from operation.

Is the repair as simple as pulling off the LU and prop and sliding in new seals?

 

[Texasmark]

Yepper.

 

[racerone]

Install a seal kit.----Less money than a complete gearcase / parts.-----Or losing a season while looking for affordable unit / new motor.