Thick black oil coming from lower unit

[riverrat321]

Hi guys, just noticed this thick black oil leaking from 2 small holes in lower unit of my relatively new 40hp Merc lite (Tohatsu 3 cyl). Should I be concerned? I thought it was gearbok oil at first but i'm hope not. I removed the bottom gear oil plug for a second and gear oil looks ok.

 

[lark2004]

Re: Thick black oil coming from lower unit

It could just be unburnt fuel and oil from inside the exhaust housing running down. It usually drips from the exaust section of the prop. Do you have the engine tilted up?

 

[riverrat321]

Re: Thick black oil coming from lower unit

No I the motor was in the down position and was used about 3 days prior. It was a real thick black oil which I have not noticed before. A fair bit of it to?

 

[TOHATSU GURU]

Re: Thick black oil coming from lower unit

Unburnt oil/fuel mix. Not to worry.

 

[riverrat321]

Re: Thick black oil coming from lower unit

Thanks for that. Haven't seen it like that on this motor. Had me a little worried.

 

[TOHATSU GURU]

Re: Thick black oil coming from lower unit

All two-stroke, thru hub exhaust, non DFI engines do it. DFI engines do it too...but not enough that anyone should really notice.

 

[Pony]

Re: Thick black oil coming from lower unit

mine does it a lot more when i idle up around the boat launch waiting for a line of people to retrieve as opposed to when i come flying in at wot and coast up to the dock. like most have said it happens to all thru hub 2 strokes

 

[bigbrownbuku]

Re: Thick black oil coming from lower unit

couls also be a cold running condition causing it, such as a stuck open thermostat not allowing the engine to reach operating temp. the result of this is more unbirnt gas washing the exhaust cavity carbon. which you see leeching thru your gearbox drains.<br />its not unusual to see this on engines that troll a lot.

 

[riverrat321]

Re: Thick black oil coming from lower unit

Yeah normally it only gets high revs but last time I did idle a bit. Will tahe it for another run soon and see how it goes. Thanks again...

 

[Moody Blue]

Re: Thick black oil coming from lower unit

This sounds to be a common occurance from these comments but I have never seen so much as a drop from mine, a 40hp 4cyl Mariner (Merc) Whats up with that? Mine gets a combination of uses from trolling to water skiing.

 

[Belchy]

Re: Thick black oil coming from lower unit

My 9.9 does it constantly, I have found that if i open up the throttle a bit before shutting it down, it helps clear it up a bit. Other than that I wouldn't worry about it. I use my Mariner as a kicker, so when its running, i am running it hard. Have also noticed that the richer i mix the fuel, the more that comes out the hub. <br /><br />Belchy

 

[TOHATSU GURU]

Re: Thick black oil coming from lower unit

The motor leg is an open cavity underneath the pwerhead that is utilized as the out-take on the exhaust system. When you are running the engine water is in that open cavity where the exhaust is blowing through it. As the exhaust hits the top of the water a lot of the unburned fuel/oil gets left there. When you pull your engine out of the water the water that was in the cavity comes out. But some of that black gunk residue drips down the inside of the leg and out the through hub exhaust. If the engine does a lot of idling, the fuel mixture is a little rich or you use crappy oil...You will see a little more of it than someone else with a similar engine.

 

[JERRYROY]

2000 johnson 40 hp are the jets the same size in uper an lower carb,

It could just be unburnt fuel and oil from inside the exhaust housing running down. It usually drips from the exaust section of the prop. Do you have the engine tilted up?

no comes out when I gett it home to flush it

 

[ezmobee]

Re: Thick black oil coming from lower unit

Please start your own thread jerryroy, this one is 6 years old.