gear oil colour

[loophole]

I have a 50 hp Merc 4-stroke, a 1999. I replaced the gear oil last year and barely used my boat this summer. When replacing the gear oil again this week I was surprised at how black my gear oil was after so little use. Is that normal?

[smitty55]

Not a big deal I would think, it likely mixed with the old oil that gets left in the gearcase when changing the oil. Of more concern would be finding metal filings or creamy coloured oil indicating water intrusion.

[RhFishing]

It could be from contaminated gear oil on the last change possibly depending on how bad it was then. It could also be the brand of oil you are using. Some oils degrade or burn alot quicker then others. Are you using marine grade gear oil or just a 80w90 gear oil? This could play a major part.

[loophole]

Thanks for your comments. I use SAE 90 gear oil. No sign of water in the old oil or metal particles. I guess the gear box is just a dirty environment, and comparing it with used engine oil is comparing apples and bananas.