woodycooper
Seaman
- Joined
- Sep 6, 2022
- Messages
- 54
I normally use Mercury or Yamaha lower unit oil which is dyed blue. When I drain it after a season of use it is normally pretty dark and no signs of water. Recently I hit something hard, destroyed a stainless prop. The shaft still looks straight, but I decided to drain the oil anyway. There was maybe a drop of water in the whole thing, nothing to worry about. I refilled it with cheap gear oil with no dye, ran the boat maybe an hour, then drained it. Pictured is a sample which looks milky to me, but others have said it could just be mixed with air from the gearcase. I took a small amount in an aluminum can and heated it up on the stove. It quickly bubbled some and within a minute it was completely clear. Does this indicate a small amount of water? I pressure tested and the gearcase holds 10 PSI or even 20 for a long time, like I let the pressure off after 20 minutes. I did not vacuum test however, but my understanding is that this would be for different temperature of oil and the outside water causing a pressure difference, sucking in the difference in water. I drained and filled again, with the same cheap gear oil and ran for approximately 160 miles, got the same result, good pressure test, looks like milky oil to me, and the same very small amount of metal shavings on the tip of the drain plug. Is this just air bubbles in the oil or is water somehow getting in? TIA, Woody