Mercury 3.3 Lower Unit Maintenance Question

adewall · #1 04-19-2009

My Mercury 3.3 2-cycle has been trouble free for the 5 years that I have owned it. I am stymied by what has been a very routine task - changing the lower unit lube oil. This year I removed the upper and lower plugs and had a small amount of fresh-looking lube drain out - maybe a couple of ounces, with no evidence of contamination. When I tried to add new oil, only a couple of ounces would go in, and nothing came out of the top opening. When I removed the lubricant tube from the lower opening, the fresh oil gushed out, as if under pressure. Several more tries resulted in the same result. I then ran the motor for a few minutes - in the water and on my dinghy. Everything worked fine - shifted into gear, seemed to have normal power, etc. Tried adding more lube to the lower end with same result.

Any ideas?

timebandit · #2 04-19-2009

Something is plugged up, try running a stiff wire in the upper hole.

Capnblu · #3 04-20-2009

I think the upper FILL TO hole is plugged. Since your little gear box isn't vented, because it runs under water and stays cool. there is no place for the compressing air to go, while you are filling it from the bottom up. So you probably just have to open this passage way and try again. Follow you MFG. recommendations for the specifics to your model.

adewall · #4 04-22-2009

Rick & Capnblu,

Thanks to you both for the suggestions. I tried probing both upper and lower fill/drain holes. A coat hangar wire went in about 1.5" on top before hitting solid object - presumably the drive shaft- and came out with a bit of fresh-looking oil on the tip; quite a bit further in on lower end without any noticeable obstructions, other than internal parts. I then tried air pressure, still to no avail - about 60 psi on top and 80+ on bottom, with no indication of flow out the other end. After releasing pressure on bottom I did get a bit of milky color flowing out, so I assume I've got a leak and probable internal corrosion. Looks like a job for the shop. I'll let you know what they find.

adewall · #5 05-10-2009

Well the mechanics are stumped. After letting my motor sit for nearly 2 weeks while working on "big" jobs, they took a look at my little Mercury but couldn't diagnose the problem - even after reportedly consulting with several other shops. Just to get me going (I have a cruise up the Bay planned for this week), they opened the lower unit, emptied out clean oil and added new. So I MAY be set for another year, but need to find another shop!