Mercury lower unit oil leak

[rascalking13]

Today I walked out to find oil under my lower unit. I'm positive this is the first day the leak has been visible, as I have used the boat several days this week including yesterday. The motor is and 89 or 90 100 hp. The leak is from a very small hole, appears to be a vent maybe? It's located just above the cavitation plate and almost in line with the shift shaft. From checking the forum I'm assuming it's a seal of some type or another. If it's an easy fix, I'll be trying it myself. Any input would be greatly appreciated, thanks! Almost forgot, the oil appears unburnt and free of water.

 

[Chris1956]

Re: Mercury lower unit oil leak

There are seals on the shift shaft and in the waterpump base. One of those appear to be the cluprits. If you are up to it mechanically, I would replace the waterpump base and seal and see if that fixes it.

Drop the gearcase, remove the waterpump cover, impeller and then clean up (with sandpaper) the driveshaft so it won't ruin the new seal. Now remove the waterpump base and lube the driveshaft with oil. Now slide the new pump base and oring into position. Install a new wearplate, impeller and 2 new gaskets. Reassemble and test.

I recommend a service manual, if you have not done this before.

 

[Gibbles]

Re: Mercury lower unit oil leak

I had the same problem, I tried the pump base to start, but I confirmed a shift shaft seal with an air compressor and a water filled garbage can with the lower off.

For the shift shaft seal it requires a special socket wrench.

I had to replace the shift shaft bushing, and the shift shaft...

be careful with the shift shaft, if you pull it out I hope you're really good at the game operation

I pulled the shift shaft bushing, and my shift shaft, replaced with new, started the threads and then took it down to a marine mechanic, he did not charge me anything to tighten it down.

 

[rascalking13]

Re: Mercury lower unit oil leak

Thanks to both of you. I'll start with the pump and go from there. I needed something to do tomorrow anyway. I can pretty much guess that it will be the more difficult of the two options, just the way it goes for me. Thanks again!

 

[carholme]

Re: Mercury lower unit oil leak

The first thing to do when you get the LU dropped is to examine the top of the shift shaft seal to see if there is evidence of oil. As you are getting the oil out of the cavity drain surrounding the shift shaft, odds are that it may be that seal.

Gerry

 

[Texasmark]

Re: Mercury lower unit oil leak

Assuming yours is a 2 cycle and the hole is just a drain for the mid section, it could easily be residual oil from the exhaust (normal) which is visible due to your recent frequent use of the engine and hence accumulation of combustion by products.

Mark

 

[ckral]

Re: Mercury lower unit oil leak

I have an 85 mercury 35 hp i just got it, working on the boat I changed the lower unit oil havent ran it but with it trimmed up in the driveway i noticed a little oit coming out of the small hole directly in front of the top vent screw Facing the vent screw horizontaly left Not sure what thi hole is Seems to only do it when i spin the prop by hand very small amount but im still concerned If oil can get out I think water can get in


Thanks Chad