Milky Colored Lower Unit Oil

[Grandview]

I have a 1980 Mercury 6 cylinder outboard motor that has had a slightly milky color to the lower unit oil when it's changed each year. It isn't significant and that's why I haven't done anything about it.

I was replacing the impleller on this motor and while I had it apart I blew on the end of a small plastic hose that comes out of the lower unit and attached to a line coming from the back of the motor. When I did this, I noticed that a small amount of air was coming from a chip/crack in the front of the lower unit housing. It's not near the bottom where the gears are but is about half way up the unit. I'm wondering if this is where the water is getting into the oil? There isn't any oil that leaks from this crack however.

Can someone help me understand this and if I should get it repaired. Also what function does this plastic tube perform. Should I be able to blow air through it normally?

Thanks for you help!

 

[86RajunCajun]

Re: Milky Colored Lower Unit Oil

If the plastic tube is connected to the front of the lower unit to a small NPT nipple then thats the speedometer pickup tube. It is prolly about as big around as a pencil.

If it is a small section of tube about 3/4" diameter then thats for the water tube.

If you have a crack in the lower unit housing, it will certainly let water in, and also the crack will get worse most likely. The housing is under load from the drive gears so it is likely weakened by the crack and could come apart while it is spinning the prop.

Sounds like you need a new lower unit.


RC

 

[AMD Rules]

Re: Milky Colored Lower Unit Oil

Have a closer look, I think you will see that that "chip/crack" is a small machined hole which leads to the tube intentionally. As Cajun pointed out, this is a factory connection for a speedo. The small hole in the leading edge of the casing is where it senses the pressure. If your bot has a transom mounted speedo pitot tube, this rubber tube on your motor is likely not used. No issues.

Milky gear oil is a sign of water ingestion. You have a leak somewhere that should be fixed if it persists. Shift shaft, drive shaft, and prop shaft all have seals on them that could leak. Typically the gearbox heats up in service then sucks water in when it cools down. A simple pressure or vacuum test could determine which seal is leaking, and how badly. It could also locate hairline cracks if you happen to have any.

Good luck.

 

[Grandview]

Re: Milky Colored Lower Unit Oil

Thanks for clarifying what the tube is for. In this case it's the speedo pick up tube.

The chip/crack in the lower unit isn't a machined hole as it has ragged edges and is irregular. It's on the leading edge of the lower unit above where the torpedo shaped part of the housing starts to appear. Should I get this welded or repaired or is it possible?

It also sounds like the unit would not pass the pressure test if I can blow into the speedo tube abd have some air pass through this chi in the lower gear housing?

Thanks

 

[AMD Rules]

Re: Milky Colored Lower Unit Oil

Interesting location for a crack. Even more interesting that you can blow air from the speedo tube out that crack. It must be cracked right through the cross-drilling for the speedo. It -may- not be cracked through into the gear oil cavity, especially if its above the torpedo. Might be worth pressure testing the oil cavity it just to see.

If it is cracked through into the gear oil cavity it will need to be fixed. If its not, you may be able to leave it alone if the crack is small enough. Speedo won't work of course. If its -not- a pressure crack to the oil cavity, I'd probably just try an epoxy weld (JB Weld for example) to seal it up and repaint for cosmetics.