Vent hole

WALI4VR

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Got a 50hp 4cycle Merc. There is a small hole on the starboard side almost at the very front of the lower unit. If the motor is tilted about halfway up it slowly seeps gear box lube! Normal? Help?
 

Ironhorse2022

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I know nothing really about 4 cyl outboards, but I’m pretty sure that lube should be in a sealed system to keep moisture out. Sounds like a leaking seal somewhere near the top of the system. Have you verified it’s not overfilled ? Hot lube expands and could have popped a seal. I’m sure somebody who knows what they’re talking about will chime in.
 

MrGiggles

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You should never have gear oil leaking externally. It's a totally sealed system.

There are three main seals to look at, the prop shaft, driveshaft (under the water pump), and shift shaft (where the shifter rod goes into the gearbox). In your case I'd put money on the shift shaft or driveshaft seal being the culprit.

There are also seals on the bearing carrier around the prop shaft, but they don't often leak.

The typical repair process consists of pulling the lower unit, draining it, setting it up in a vice and then pressure testing it through the fill/drain plug with a Mityvac style pressure/vacuum tester. Identify the leaking seals with soapy water, replace, test again. Some models will require disassembly to replace the shift shaft seals, but the prop and driveshaft seals can usually be pulled and replaced without.
 

Pappy

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check the simple things first how about it?
Right off the bat folks are assuming you are correct in your diagnosis. That may lead to an unnecessary and expensive repair.
Any vent hole in the mid-section/lower unit area is there to purge water so that freeze damage does not occur.
It is fairly normal to see some unburned fuel residue exiting these vent holes along with the water that is draining. Wipe some off and smell it first.. Burned gasoline smell or gear oil smell?
Secondly if you have gear oil exiting the gearcase and out the drain hole then you will or should have water entering your gearcase as well. Check it!
 

MrGiggles

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check the simple things first how about it?
Right off the bat folks are assuming you are correct in your diagnosis. That may lead to an unnecessary and expensive repair.
Any vent hole in the mid-section/lower unit area is there to purge water so that freeze damage does not occur.
It is fairly normal to see some unburned fuel residue exiting these vent holes along with the water that is draining. Wipe some off and smell it first.. Burned gasoline smell or gear oil smell?
Secondly if you have gear oil exiting the gearcase and out the drain hole then you will or should have water entering your gearcase as well. Check it!

I would've said the same, but I've never seen a four stroke drool like the two strokes do.
 

airshot

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First post says 4 cycle, but second post says 4 cylinder..which is it or a typo ??
 

eeshaw

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Can you provide a pic? What year are you talking? If worse comes to worse I have one from a big foot model available.
 

eeshaw

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I don't know about the 50 for sure, but I do know that Mercury made 4 stroke 4 cylinder models of the 60.
 

LDUBS

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OK, I know I am going to be the cause of much eye-rolling. I apologize in advance.

That hole on the side of the lower unit. Is it by any chance where the gear oil fill plug should be?
 

Pappy

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OK, I know I am going to be the cause of much eye-rolling. I apologize in advance.

That hole on the side of the lower unit. Is it by any chance where the gear oil fill plug should be?
Let me be the first to roll my eyes then. The comment was made that gear oil was visible or at least what he thinks was gear oil. If the vent plug was out the assembly would have had nothing but water and probably metal shavings in it by now. Possible? Anything is possible. Probable? Nope.
 

eeshaw

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He hasn't been on the site since the 8th. It sounds like the speedo hole on the front of the lower unit.
 

LDUBS

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Let me be the first to roll my eyes then. The comment was made that gear oil was visible or at least what he thinks was gear oil. If the vent plug was out the assembly would have had nothing but water and probably metal shavings in it by now. Possible? Anything is possible. Probable? Nope.

I knew I was kind of on thin ice. Thanks for bringing me back down to earth.

He hasn't been on the site since the 8th. It sounds like the speedo hole on the front of the lower unit.

That is what had me scratching my head. He says it is on the side near the front. My outboard has nothing like that, but mine isn't a Merc either.
 
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