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oil leaking from weep hole

newboatowner222

New member
I have a 1989 Mercury 90 hp 6 cylinder outboard and I noticed clear oil dripping out of a small weep hole just below the bulge on the lower unit. Any ideas?
 
Hi newboatowner222,welcome to a very enjoyable,wallet hammering hobby,:D
'89 90HP 6cyl??? Could you post the number? You'll find it on the transom bracket.If it's not there a couple of pics might help. Is that the fill bung you say the oil is leaking from? You fill a lower unit from the bottom, try tightening the bung,if that doesn't stop the leak,you need a new gasket or O ring.That's the lower unit lube that's seeping out
 
If you are sure it is gear oil and If it's weeping out of a casted smooth hole, chances are you have a leak in the input shaft or the shifter shaft. Drain the lower and remove it. Remove the upper water pump cover so you can see the seal, pump about 10psi into the lower and look for the leak.
 
If that's what I think it is, it's no big deal. To prevent freeze cracking in cold weather, Merc drills small drain holes in the LU. Oil from combustion always drains out the bottom, and that's what you're seeing.

Jeff

PS: Try vacuum testing the LU instead of pressure. If it holds a vacuum, go boating!
 
Jeff:

I am taking the boat next week to a dealer. Should I suggest as a first step not remove the LU and vacuum test? The motor I believe is 1978 or 1980 vintage. You are the 2nd person to suggest this can be normal seepage for the older motor?

Thanks
 
Could be normal and the only way to find out is to do a pressure test ( witness it ) at a shop.-----------Guessing does not work and can be expensive.
 
Agreed. You wouldn't believe how many perfectly good LUs get rebuilt after someone sees aerated oil and assumes it's water intrusion.

A vacuum test is easy to do at home and does NOT require LU removal. You need a Mighty-Vac or other form of vacuum pump with a gage. (AutoZone might have one you could borrow, like other auto tools.) The drain plug is a 3/8 UNC thread, so you need to adapt an 1/8inch pipe by 1/4 inch barbed fitting to make your test fitting: Thread one end 3/8 UNC, and hook a vacuum hose to the other end. Next, elevate the LU high as possible or you'll suck the oil out. (I usually drain the LU first.)

Then pull a vacuum. If it holds, go boating! If the reading comes right down to zero, the seals are leaking and you'll need to reseal the unit. Ignore pressure testing as it doesn't do a thing for you.

Jeff
 
You wouldn't believe how many perfectly good LUs get rebuilt after someone sees aerated oil and assumes it's water intrusion.
Only if you use a cheap automotive gear oil as all gear oils are not the same. Most cheap automotive gear oil does not have the foaming additives due to it runs in a vented housing whereas a outboard need the anti foaming GL4 minimum. Usually aerated oil is still the color of oil or yellow baby poo, milky grey or white is water intrusion. Also the reason gear oil turns "smelly and black" is that it is is decomposing from heat and shear. The smell is hydrogen sulfide a by-product of oil breakdown. Usually the main reason this happens is the wrong weight oil is installed or a cheap automotive gear oil was used in the unit. Marine gear oil has anti-foaming agents, extreme pressure additives and emulsifiers to help prevent oil breakdown in case of water intrusion. Auto/trucks use a vented gear housing so foaming/heat is not a critical problem and are not subject to exhaust heat transfering thru gear housing.
Ignore pressure testing as it doesn't do a thing for you.
Always pressure test as it will show any leaking o-rings in carrier,water pump base,drain screw gasket and shift bushing areas with a squirt of a soapy solution. That the reason repair manuals suggest you do both as its a complete test. Hard to find a leaking o-ring when vacuum testing as it sucks testing solution inside unit.
 
If you are sure it is gear oil and If it's weeping out of a casted smooth hole, chances are you have a leak in the input shaft or the shifter shaft. Drain the lower and remove it. Remove the upper water pump cover so you can see the seal, pump about 10psi into the lower and look for the leak.
Thanks this helped me fix my free boat! Can I use grease to fill after repair?
 
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