Lower unit question

[Lostbay]

Draining my gear oil last night(40 hp merc) I noticed it was black, not milky or watery in any way. Now granted I started with the oil that is dark blueish, but I was a little surprised by black after one year and around 30-40 hours of use. My primary question is that I seem to have a little dark liquid coming from where the prop meets the lower unit (right where it spins). I know the motor vents through the end of the prop but this is buildup at the seam of where the prop spins and the rest is stationary.

Strangely enough I did smell it and it doesn't quite have that distinctive lower unit oil smell, more like combusted gas (but hard to pinpoint). I thought I must have a leak on a seal behind my prop, but the gear oil seemed water free, albeit dark. Can this just be dirt and/or combustion products and not indicate a seal failure? Or are there seals that could be out that have nothing to do with the gear case? If I take the prop off I wouldn't even know what to look for on my seals. Thanks

[reinhard1]

i saw the same thing yesterday when i drained my son-inlaws 35 Evinrude. i also had a dark blue grease i put in last fall. he is not having any issues but i am also concerned of seals that need fixing or is this normal with older motors. i think its a 84 year motor. thanks good luck.

[CAMAN]

Perfectly fine and normal. It's just unburnt 2-cycle oil draining from the combustion chamber/exhaust.

And the darker lower-unit lube is normal as well.

[CAMAN]

If I take the prop off I wouldn't even know what to look for on my seals.

You should pull off the prop on a regular basis throughout the year to inspect the shaft and sealing area for fishing line and rope that could be wrapped around the shaft. Otherwise I like to pull out the top plug on my lower unit to inspect the oil and make sure it's not milky and not leaking out.

[reinhard1]

Thanks. good luck.

[8-Ball]

Its normal-no worries, as others have chimed in.

[jwmiller33]

Exhaust

[Hoffer]

I had put a similar question on here last year. Everyone responded that its just exhaust. When i put my boat in the garage after use - and have the motor down - I always get a little spot of black oil on the floor. I guess its just normal and is from the exhaust. I just had my lower unit completely redone this spring - so I know it has brand new everything - and it still left a small spot of black oil on the garage floor. I also do a lot of trolling around 3 to 4 mph - and I imagine that builds up some oil that is not getting properly burned off like if i was going all out at high rpm's all the time. Anyway, as long as you dont see water when you change your lower unit or you dont get the milky look to the oil - I would think you are good to go.

[Surface Tension]

As said the little black oil dripped on the floor is just residue from the exhaust.

Black gear oil drained the lower gear case is another matter.

It shouldn't discolor like that. If you start out with dark blue oil a little oxidation from the aluminum case or brass could turn it darker.

[jwmiller33]

I just had my lower unit completely redone this spring - so I know it has brand new everything - and it still left a small spot of black oil on the garage floor. I also do a lot of trolling around 3 to 4 mph - and I imagine that builds up some oil that is not getting properly burned off like if i was going all out at high rpm's all the time.

It's funny you mention you do a lot of trolling and notice the black exhaust spot on your garage floor. I didn't have the black exhaust stuff coming out of my motor until last year when I picked up leadcore trolling and started doing a ton of backtrolling with my rig (35hp). After one night of trolling for 6 hrs straight, I had some black exhaust stuff slowly oozing out of my motor while in the garage. I came on here and posted the question as to if I should be concerned about it. Now I know!!!

[Hoffer]

Hey JW

Just wondering why you backtroll with the 35? You should be able to dial that down pretty slow for your leadcore...or do you troll that REAL slow?

Most of my trolling with the bigger engine (75HP merc) is done at around 3 to 4mph. I have gone literally all day trolling at that speed - so I know that black drip on my floor has to be from the oil not being properly burned off. But Ive been doing it for years now with absolutely no engine troubles.