Engine Gear Case Oil Leak

Old 08-19-03, 04:27 PM
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85 HP Force Engine Gear Case Oil Leak

85 HP Force engine, 1986

Just noticed lower gear case oil drip marks coming from what appears to be 2 small predrilled holes under the cavitation plate towards the front of the engine, on both sides. Otherwise, engine and gears seem to be working fine. Also, the lower gear case oil was replaced in the beginning of the season. Used the engine this weekend to waterski and 3 times before that since the oil was changed. Was wondering what caused this to happen since I've never noticed it before.
Old 08-19-03, 04:55 PM
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Also, just noticed that there are actually 3 (1/8 inch weep?) holes on each side of the engine under the cavitation plate. But only the 2 holes on each side in front dripped gear case oil.
Old 08-24-03, 09:35 PM
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Gearcase lubricant is usually golden in color, whereas
unburnt two cycle oil is dirty green.
What have you got ooozing from your case.?
Old 08-30-03, 06:55 PM
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Mercury High Performance gear oil is also dark green in color, and the new Mercury Optimax Synthetic two-cycle oil is golden brown.

Don't rely on fluid color alone.

If you are leaking from the upper fill/vent plug (Does it have a flat bladed screw head in the holes) it's a symptom of an overfilled gear case. It's also possible (unlikely, if you used a certified mechanic, but still possible) that the mechanic didn't replace the fiber gaskets on the plug(s) with new ones, or didn't remove the old gaskets before putting on the new ones.

This can also indicate leaky seals in the lower unit. As oil leaks out, it's replaced by water. As it churns in the gearcase and mixes with the remaining oil, it will froth up and "pressurize" the gear case, forcing oil out of the plugs (among other places). A lower unit will run for a while on 100% water in the case, but not for long before it self destructs. (don't ask me how I know this)

If you determine that it IS gear oil, have it changed immediately, and have the case pressure tested for leaks.

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