What causes lower unit lube to turn BLACK, I mean REAL BLACK???

[BIGFLAT]

Drained my lower unit this morning and the lube that came out was black as tar. I can't ever remember it looking like that. Do I have something wrong in my lower unit, or is it some kind of reaction. I keep my old lube to check for water, and I had the same volume of lube as the last change. Since I change it ever 4 months, I use the Walmart brand. My theory is it's cheap insurance if I have seal problems in a 16 year old lower unit. Thanks...BF
Speaking of outboard fluids, There was a post somewhere asking about changing the power trim fluid in an outboard. Any one ever hear of doing that???

 

[wired247]

Re: What causes lower unit lube to turn BLACK, I mean REAL BLACK???

I suppose you could change trim fluid whenever you want but its just hydraulic oil. Unless you are low in fluid its not going to help changing it. It never gets hot.

 

[woody66912]

Re: What causes lower unit lube to turn BLACK, I mean REAL BLACK???

Try this get a name brand gear lube, refill and in four months or sooner check it if it's black then you could have a bearing on it's way out, it shouldn't be a shimming issue. as the issue just popped up. I would tend to think it is a product issue.

I recommend the BRP brand in this case, it's clear so when you go to check it you can see just how black it has turned.

 

[hotrod53]

Re: What causes lower unit lube to turn BLACK, I mean REAL BLACK???

+1 on name brand lube, its not gray and its not metalic looking .. thats all a good thing. Sounds like cheap lube. Maybe a good flush is in order on the next refill? You could use cheap lube to flush with.

 

[schematic]

Re: What causes lower unit lube to turn BLACK, I mean REAL BLACK???

It is common to see black Lu oil if the unit was underfilled. Underfilled means poor heat conduction to the case, thus the oil overheats. Find out what your gearcase holds, and measure what you put in....

 

[Faztbullet]

Re: What causes lower unit lube to turn BLACK, I mean REAL BLACK???

The reason the oil turns black is due to it decomposing. This happens to oil with lower EP additives and automotive gear oil used in a sealed unit(auto gearboxes are vented). The oil as it breaks down(decomposes) it creates hydrogen sulilde( the stink of black oil) and heavy loading. Only use a good brand name oil.

 

[Scott Danforth]

Re: What causes lower unit lube to turn BLACK, I mean REAL BLACK???

+ 100 on using a quality oil. you may have saved a dollar on the walmartian oil, however your changing it every 4 months. a good quality brand of oil would last longer and ultimately cost less.

 

[BIGFLAT]

Re: What causes lower unit lube to turn BLACK, I mean REAL BLACK???

Thanks to all for your input. I have given this black lube a lot of thought since yesterday. My recollection is that when ever I send my engine out and have the lower unit repaired or water pump replaced, the repair shop changes the lube. The next time I change it, its darker than when I change the lube. I just recently had cooling problems after I changed the water pump, so I had a repair shop do it over. ( gasket was not installed correctly). I told the guy who 'took it in' the lower unit lube had just been changed and it did not need replacing. I'm thinking the guy who did the impeller changed the lube. I'm gonna keep a close eye on the lower unit and see if the lube gets dark again...BF

 

[Alumarine]

Re: What causes lower unit lube to turn BLACK, I mean REAL BLACK???

On my Merc 50 it get's completely black and I use Quicksilver high performance synthetic.

 

[Faztbullet]

Re: What causes lower unit lube to turn BLACK, I mean REAL BLACK???

I use the Sierra synthetic gear lube(Part#18-9680-2) as its meets the Volvo specs.. and when you change it a year later it almost as clean as the day installed!!!!