Oil very slowly drips from my 2007 50HP Yahama lower unit area

[kodak guy]

When I tilt my motor up out of the water, I notice an oil slick forming around my pontoon boat. When the motor is fully down, I see no oil slick. I have no trailer for the boat so all my diagnostics are done while leaning out and over the motor and splashing water on it. I wiped down the lower unit with dawn dish soap to remove any existing oil.This is what I observe. Oil is not coming out of the gearbox fill or level holes. Oil is not coming out the propeller area. The engine compartment is clean. No oil dripping from the oil filter or anywhere else around the engine that may be dripping down to the lower unit. What I do see now with the motor trimmed fully up is oil on the middle fin. This fin is located just under the top most fin that sits just above the nuts that secure the gearbox to the rest of the lower unit. There's not much room between the top fin and the middle fin. About 3/4 of an inch maybe. Oil slowly collects on the upper surface of this fin until it drips. As the boat is in the water, I can't see where the trail of oil starts. I plan to have the boat taken out of the water in a couple days to investigate further. Could I have a bad seal on the drive shaft or if there's a seal where the gearbox bolts on, a bad seal there? Once the boat's out I'll be able to drain and check the color of the gearbox oil once I see where the leak may be coming from. Thank you

[99yam40]

Is it lower unit lube?
it smells a lot different than other oils.
reach out and touch the oil drip and then smell it

[kodak guy]

smell the oil

thanks 99yam40 I'll give it a whiff.

[99yam40]

if it is lower unit lube, it will be from the driveshaft seals in lower unit.

other oils can run down the drive shaft from the power head.
you did not say this was a F50 or T50 so I guess this is a 2 stroke.

pay attention to the color of oil too, is it clean or black/burnt looking

[kodak guy]

Lower unit oil drip

Thank you for the reply. This is a 4 stroke t50tlr. It's on a 20' pontoon boat that until recently had never been run at full throttle for any length of time,( my grand daughter just got a tube for me to pull her around in). I'm the original owner. Other than plugs, oil, filter and gear lube, it's never been serviced. I'd like to take the "apron" off, the cover just below the power head lower cover, but I'm sure there's more to it than removing 2 screws. I can't find a procedure. If oil is coming from somewhere up toward the power head,i'd think I'd see it in this area maybe. Thanks again!

[99yam40]

smell it 1st to rule out lower unit lube.
have you check the motor oil level?

If the lower unit has to come off, you can back it up to a low dock with motor tilted up to pull it if you do not want to put on a trailer

[pstephens46]

In addition to finding oil leak, you need to replace water pump if it has never been done.

[kodak guy]

Thank you. I kind of figured I'd have to rebuild the water pump as long as it has to come out to access the drive shaft seal. Kind of worried about the woodruff key being stuck in the slot in the drive shaft. The boats only been on Minnesota lakes so hopefully the key will come out without too much urging.

[kodak guy]

Hey 99yam40, the oil I saw forming into a drip on the middle fin getting ready to drop into the water looked like brand new, clean motor oil, I believe. I guess I haven't really paid much attention to the color of the yamalube gearcase oil or what it smells like. I will soon. Thanks

[99yam40]

Not sure about the Yamaha lower unit lube, but all the stuff I have used stinks, does not smell like motor oil

[Gabe Armstrong]

If equipped you may want to check the power lift cylinder seal,

[kodak guy]

Lower unit oil leak update. The boats out of the water, so I can now inspect the unit.Checked the level and drain plugs for leakage and found them to be fine. Removed the prop and removed a small amount of fishing line between the thrust washer and seal. Looked pretty good around the prop shaft. No oil residue and the fishing line removed was not saturated with oil. I drained the oil and did have about 2 ounces of water come out, then the milky oil. I then refilled the unit with new oil, cleaned everything up and trimmed the motor fully up to see if it will leak again and where. If I don't see anything, I'll put it back in the water and run it around for a bit and see what happens before I pull the unit and have it pressure tested.
Thanks for all the input!

[99yam40]

I guess you can now tell the difference between lower unit lube and motor oil, correct?.
most people would pressure test when they had the unit drained.
but you need to drain and flush the water residue out anyway.

hope the water did not sit in the unit and rust up gears and brearings

[scofflaw]

Not sure why you want to run it around to see what happens. Get it resealed and then flush it a couple of times with some cheap motor oil. You can do all that with a garden hose in your driveway.

[panasonic]

Lower unit oil leak update. The boats out of the water, so I can now inspect the unit.Checked the level and drain plugs for leakage and found them to be fine. Removed the prop and removed a small amount of fishing line between the thrust washer and seal. Looked pretty good around the prop shaft. No oil residue and the fishing line removed was not saturated with oil. I drained the oil and did have about 2 ounces of water come out, then the milky oil. I then refilled the unit with new oil, cleaned everything up and trimmed the motor fully up to see if it will leak again and where. If I don't see anything, I'll put it back in the water and run it around for a bit and see what happens before I pull the unit and have it pressure tested.
Thanks for all the input!

Not much point of putting it back on...you have a bad seal or seals on the LU. May as well fix it now properly before you do any permanent damage.