Merc 50HP leaking oil

[MercMan2004]

Hi...<br /><br />I have a 1984 Merc 50 that seems to be leaking small amounts of oil from the lower unit.<br /><br />Specifically, it appears to be coming from a small rectangular notch found on the leading edge (ie the side facing the boat).<br /><br />I have not been able to find any reference regarding that notch in my Seloc Repair Manual. It is about 1/2" long and 1/4" wide. Next to it is a small circular hole. It is at the same level as the Lubricant Vent plug, but its over at the leading edge. It is only one one side of the unit (although there is a similar small circular hole on the other side as well).<br /><br />Does anyone know what that notch (and circular hole) are for?<br /><br />Why would there be oil coming from it?<br /><br />Could this be a sign that a gasket/seal in the lower unit is the problem??<br /><br />Any advice would be greatly appreciated.<br /><br />Thanks<br />Dave

 

[rickdb1boat]

Re: Merc 50HP leaking oil

Sounds like unburned fuel. Normal stuff. rub some between your fingers and give it a smell. If it smells like gas/oil, you are OK. The notch could be a water drain to make sure there is no water left in the exhaust housing so it does not freeze when the temps are low or it could be a water intake. I'm not real familiar with the Mercs, but others will know for sure.. I think you are fine, though..

 

[Chris1956]

Re: Merc 50HP leaking oil

MM2004, I suspect the notch and hole are designed to allow any water remaining in the exhaust passage above the lower unit, to drain out, when the motor is on dry land.<br /><br />The lower unit should not leak oil, anywhere or anytime. Make sure it is lower unit lube, and not 2 cycle oil(hint, if it stinks, it is gear lube). If it is gear lube, replace the waterpump base, oring and gaskets. The waterpump base has two seals which although can be ordered seperately, are not much cheaper than buying the base with them already installed. Also, replace the impeller, while you have it apart.

 

[MercMan2004]

Re: Merc 50HP leaking oil

Thanks for your responses.<br /><br />I'll take a closer look and see if I can determine if its gas/oil. <br /><br />Thanks<br />Dave

 

[Keith Buchanan]

Re: Merc 50HP leaking oil

Welcome Dave, you've found the right place..<br /><br />I think the notch you are refering to is the pitot tube cavity, the small hole you see is the end of your pitot tube and almost certainly what you are seeing is the residue out of your exhaust. Please check though and the easiest way is to change your gear oil and see:<br /> <br />a: How much old oil drains.<br /><br />b: What colour is the old oil.<br /><br />Post back your findings..

 

[MercMan2004]

Re: Merc 50HP leaking oil

Hi again..<br /><br />I checked this weekend and I can't tell if its oil/gas or gear oil, at least not by smell - it doesn't leak enough to tell. I can only tell something is happening by the signs in the water.<br /><br />It is not constant, but rather I see oil residue in the water when the engine is raised or the boat has rocked side to side (while at dock). Otherwise nothing. <br /><br />I can't actually drain the gear oil without pulling the boat out of the lake which is not a straight forward process (boat launch is on the other side of the lake). However, I removed the Vent screw and I could see that the level of the gear oil was still high and its colour did not indicate major water contamination.<br /><br />I'm wondering if I have a bit too much oil in my fuel mix and would that explain why there would be this more than usual residue coming from the exhaust? <br /><br />Here is a picture of the notch and its location. I'm not sure what a Pitot Tube Cavity is used for (some kind of flow/speed monitoring??) Any comments greatly appreciated.<br /><br />

<br /><br />Thanks<br />Dave

 

[MercMan2004]

Re: Merc 50HP leaking oil

Bump..<br /><br />Any last comments about that notch? is it a pitot tube cavity?<br /><br /><br />Thanks<br />Dave

 

[MercMan2004]

Re: Merc 50HP leaking oil

Hi.. just thought I'd post a follow-up:<br /><br />The end result was that it wasn't just unburned feul but a seal near the shift-shaft that was leaking.<br /><br />I still don't know what that notch is for, but it certainly looks like its designed to direct water into the lower unit when the boat is underway. Whatever it is for, if you see any residue coming from it, then its a seal problem.<br /><br />D.

 

[andrewkafp]

Re: Merc 50HP leaking oil

That notch is on all Mercs near the front and any excess fuel/oil that leaks from the carbs or any anti corrosion spray that you use will run down the shift shaft and into that area and any excess drips out of those holes.<br />If it doesn't clearly smell of gear oil (Very distinctive) it's just a combination of the above lubricants dripping. Unburnt 2 stroke usually comes out around and out of the prop.

 

[MercMan2004]

Re: Merc 50HP leaking oil

Thanks for your reply..<br /><br />Question I have is if that notch is simply for venting why is it shaped/designed to force water in? <br /><br />I can see the circular hole next to it being a vent (and there is a similar circular hole on the other side as well but the rectangular notch is only on one side). However, I noticed nothing coming out of the circular holes, which would suggest that the notch and the round holes are not physically connected.<br /><br />I bought this engine new in 1984 this was the first year I noticed anyting coming from it.<br /><br />I never was able to positively identify the oil as being gear oil or gas/oil but I now know it was gear oil.<br /><br />D.