Black Lower Unit Oil

[cousincletus]

I have a 1994 Sunbird boat with an Evinrude 48-SPL. The lower unit calls for synthetic oil, so I have been using Amsoil 75W-90 gear oil in it. This is not the marine Amsoil, but the regular GL-5. I drain and refill the oil every year, and for the past couple of years the oil has come out black. There is no indication of any water getting into the lower unit and nothing on the magnetic drain plug. Also I can't see any particles of any kind in the drain pan after I drain it. Does the color matter and is this normal? Could this be a sign of something about to fail in the lower unit? Thanks for the help.

 

[1 FMF]

I have drained lower units and have seen the oil black. I think the longer you run the oil, or if you put many hours on it per season, the more chance it's going to darken. I'd prefer it to darken than come out milky white. Only thing I can think of why it's darkening is due to oxidation, which may be normal depending on the service interval. It may also be due to the unit running hot due to bearings and/or gears wearing and parts falling out of tolerance. A used oil analysis would probably help a lot, with a oxidation count and particle wear count it might tell you if it's normal or not.


How many hours do you put on the gear oil before changing it?
I run my 2002 19' with a merc alpha sterndrive at 4000 rpms all the time skiing, I put at most 50 hours a season and the merc gear oil comes out green/blue, just like it went in.

 

[cousincletus]

Change it every year and run about 20-25 hours per year. I'll switch over to a marine specific lower unit oil and see what happens. BTW the Evinrude 48SPL calls for synthetic oil. The drain plug has a magnet and it didn't have any shavings on it.

 

[dypcdiver]

I have just drained the oil from my Volvo DP-S outdrive and it is also very black. This oil has been in there for about 90 hours use and not had too hard a life. It was put in to replace the original Volvo spec oil (120hr use) which when drained came out clean and clear. The black oil is a GL-5 synthetic own brand from a local parts shop here in Spain. The oil smells but not an overheated type of smell and there is no trace of particles on the magnet or any water in the oil. Has anybody done any research on this? I have seen something similar reported on an auto club site. I have also asked if anybody can do an analysis locally but only got blank looks.

 

[Ilikesynthetics]

I too have used, (and still do) use the Amsoil lube you are using. I have never had it come out black, always looks just like it did when I put it in even after 50 hrs or even more. I would use the new marine gear oil if it came in gallons.

 

[Ryan00TJ]

The Quicksilver Synthetic I change from my Alpha 1 every fall comes out looking almost like when it came in. It usually has 50-75 hrs on it.