1992 Mercury 25HP - lower oil leak

Mattos17

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Dec 29, 2011
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Hi All, I have just purchased a 1992 Mercury 25 HP, that I have taken out for a run about 4 times and is running well. However after a washdown and flush I have noticed a small amount of oil leaks from just under where the prop is bolted on - it leaks for the next day or so. The leaking oil seems very similar to the 2 stroke oil I am using. Is the leak just unburnt 2 stroke oil, or is there possibly a gearbox or gearbox oil leak problem ? Thanks - any help appreciated.
 

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Mi duckdown

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Apr 14, 2007
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Re: 1992 Mercury 25HP - lower oil leak

Lack of info. 2 stroke or 4 stroke and serial number.??
After re reading post it is a 2 stroke Correct?
 

Mattos17

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Dec 29, 2011
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Re: 1992 Mercury 25HP - lower oil leak

Hi All, I have just purchased a 1992 Mercury 25 HP, that I have taken out for a run about 4 times and is running well. However after a washdown and flush I have noticed a small amount of oil leaks from just under where the prop is bolted on - it leaks for the next day or so. The leaking oil seems very similar to the 2 stroke oil I am using. Is the leak just unburnt 2 stroke oil, or is there possibly a gearbox or gearbox oil leak problem ? Thanks - any help appreciated.

Yes, it is a 2 stroke - serial ODO88513 - thanks
 

Texasmark

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Dec 20, 2005
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14,544
Re: 1992 Mercury 25HP - lower oil leak

On the bottom side (probably starboard..right side looking forward) of the bulge in the lower unit casting that is the housing for your drive gears and the prop shaft sticks out the back, is a little SS plug slightly smaller than a dime.

With the engine having not been run for a week or so, and sitting vertically for that time, slowly remove that screw (lower unit drain plug) and carefully monitor what comes out first, and you only need to let enough out to determine the color. If blue black oil comes out fine. If it has any chocolate or yellow coloring to it then you have an oil leak and it could be your rear seal on your prop shaft.

Otherwise it is the oily residue from the 2 cycle oil burning process and is normal. The actual amount depends upon the ambient temperature and how you use your engine.

HTH.

Want more ask.

mark
 

Mattos17

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Dec 29, 2011
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Re: 1992 Mercury 25HP - lower oil leak

Thanks Mark,
It has been a week since last use, and sitting vertically - and the oil leak from under the prop stops after about a day.

When i remove the lower unit drain plug, a very small amount of dirty water drains out. Nothing else there.

What do you think ? Can i still use the motor in the meantime ?

I appreciate your help

Matt
 

sutor623

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May 23, 2011
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Re: 1992 Mercury 25HP - lower oil leak

When i remove the lower unit drain plug, a very small amount of dirty water drains out. Nothing else there.

What do you think ? Can i still use the motor in the meantime ?

Matt

WHOA WHOA Buddy! When you removed the drain plug you got some dirty water and thats it?? Did you just decide to leave the top drainage vent plug in, or is this when you pull it out? If I were you I would drain ALL of the lower unit oil out, into a CLEAN container, and check it overnight for water/oil separation. If there is water in there then your answer is NO you should not be running this motor until you change the prop shaft seal, and the two seals that go behind the drain/fill plugs. Especially if it is cold outside where you are right now. I can send you some pics of one of my lower unit that had water in it that set out in the cold if you want to see a $5-600 boo-boo.....
 

sutor623

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May 23, 2011
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4,087
Re: 1992 Mercury 25HP - lower oil leak

Oh and by the way, I had an exhaust gasket go in one of my lower units, and the water and air exhaust ports mixed. I got some unburnt 2cycle oil/fuel leaking from where the prop meets the actual housing. If this is the case then you are fine, just need to change the exhaust gasket next time you have the L/U down for waterpump service.....
 
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