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?
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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.You wouldn't believe how many perfectly good LUs get rebuilt after someone sees aerated oil and assumes it's water intrusion.
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.Ignore pressure testing as it doesn't do a thing for you.
Thanks this helped me fix my free boat! Can I use grease to fill after repair?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.