Lower Unit Oil Leak

[JimS123]

2019 Mercury 4-stroke 150 HP.

Looks like a minor leak emitting from the rear end of the lower unit, where it bolts on. The motor has very low hours and is always garage kept. Fresh water only. I noticed a slight drip of oil after sitting all Winter. The oil is puddling on top of the AV plate and dripping off the end. After 6 months of sitting I estimate the leak at less than an ounce.

My thought is to tighten the 5 bolts holding the lower unit on, check to be sure the gear oil is full, and monitor the leak.

Anybody suggest a better approach?

(The pic shows the motor tilted up - it was horizontal all Winter)

 

[Mc Tool]

1st thing to do is to be sure its gear oil and not engine oil ......no chance you spilt oil whilst topping up the engine . You can usually tell by the smell of the oil what it is .
Tightening the lower unit mounting bolts wont help .

 

[JimS123]

1st thing to do is to be sure its gear oil and not engine oil ......no chance you spilt oil whilst topping up the engine . You can usually tell by the smell of the oil what it is .
Tightening the lower unit mounting bolts wont help .

My plan was also to check the engine oil. But if it was, how did it get down there?

A spill is not feasible. I wipe everything down meticulously. I'll give it a try, but I don't think there is enough there to get a good smell.

Why won't a bolt tightening not help? I'm assuming some came loose after 6 years.

 

[jlh3rd]

those lower unit bolts have nothing to do with sealing anything. The just hold the gearcase on.
The nuts are nylocks so not prone to loosening.

 

[roscoe]

Tightening won’t help because that is not what seals the gear oil in.
There are seals on the driveshaft and the shift shaft.

“I'm assuming some came loose after 6 years.”

They should have been loosened/removed when the water pump impeller was replaced. If you haven’t done that yet, it’s time.

When you remove the gearcase to service the water pump, you can inspect to see if it is engine oil or gear lube, and whether a seal has failed.

 

[airshot]

Would be kinda unusual for gear oil to be above the cav plate....Have you checked the gear case oil for water intrusion or low level ?