Mercury 2 stroke question:

[Juan]

I bought an old bass boat with a Mercury 115 - 2 stroke the other day. Is it normal to have a little oil leak from inside the prop after running the motor? I don't remember any of the 2 strokes I've owned previously doing this but it's been years since I've had a 2 stroke.... It appears to be burnt oil and I'm guessing it's oil from the 2 stroke oil mixture the engine uses since it comes from inside the prop where the exhaust comes out?? I was a bit worried that it might be a bad prop shaft seal but the seal doesn't appear to be leaking and the oil stops running out after the engine cools.. I checked the lower unit and it's still full of uncontaminated oil so I don't know where else the oil could be coming from...I've just never seen this much oil from a prop exhaust before... (I'm guessing a couple of ounces after running the motor with muffs)

[freezerfiller]

I've seen that when you have a carb for each cylinder and one of them is flooding one cylinder due to a stuck needle/sunk float. Might pull your plugs and see if you have one that looks real shiny...

[Juan]

Thanks, I'll check that but the guy I bought it from is a marine mechanic and told me he had just rebuilt all the carbs... (but he was selling the boat and might say anything)

[985crabs]

I had an Evinrude that did what you're saying. I put cardboard under it and let it get a good soaking. Took the cardboard to my mechanic and showed him and he said it was fine. Might be a leaking seal in the exhaust manifold or something like that, but as long as it was post-combustion it doesn't matter. I'm assuming it's dark and burned smelling.

[Juan]

Feb 16, 2015 16:52:46 GMT -6 985crabs said:

I'm assuming it's dark and burned smelling.

Yep, it is...just seems like there's a lot of it.

[gnrphil]

Imo That is not normal, I would say it's over oiling in a big way.

[Juan]

Could it be that there's more than a 50 to 1 oil / fuel mixture? It had a 1/4 tank when I bought it and I have no idea how much oil was mixed with the fuel.

[985crabs]

That looks like quite a bit. Does look like there's so much oil in the gas it can't burn. I'd start with a new batch of fuel and see if it persists.

[gnrphil]

I guess it has a vro system, disconnect that and run it on a separate tank of premix and see what you get.

[Simple Man]

Does it smell like lower unit oil? Gear oil has a special funk about it. My guess is all that is not unburned two cycle oil.

[Juan]

Feb 16, 2015 20:29:23 GMT -6 Simple Man said:

Does it smell like lower unit oil? Gear oil has a special funk about it. My guess is all that is not unburned two cycle oil.

That's what has me puzzled... it doesn't smell like lower unit oil and it's darker (like the color of quicksilver 2 cycle oil).
The VRO system was disconnected by the previous owner and the fuel is now mixed. The thing runs like a new one.. barely touch the key and it fires right up but the oil bothers me.

The oil only leaks after I run the motor...It leaks what looks like an ounce or two then quits... There is no leak when it's just sitting there.

I've checked the lower unit oil and it looks good and doesn't seem to be getting any lower. If it's not the lower unit leaking, then I'm guessing it must have something to do with the oil in the fuel mixture since to the best of my knowledge, that's the only other oil source.

I put another 6 gallons of fuel in it, but I always mix the oil a little heavier than 50 to 1, so I may have to run it all out and start over to be sure it's not the mixture.

[Simple Man]

It would be smoking like a skeeter truck it it was over oiling that much. It's either leaking it externally and running out there some way or that's lower unit oil. I'm not buying that much unburned 2 cycle oil is coming through unburned with out serious missing issues or fog truck smoking.

[Juan]

I tend to agree that it would be smoking if it were unburned two cycle oil and it isn't....but still don't understand where the oil is coming from since there is no oil at all leaking out when it's just sitting there and only after it's been running. I might understand if the oil showed up after the motor has been run in gear... that would prove the prop shaft seal is bad and leaking but it's been run in neutral, so the prop shaft wasn't turning.
I give up.. I'm going to run it until something gets worse or blows.

[gnrphil]

If it were "unburnt" oil it wouldn't be smoking beacause it's unburnt, no smoke without fire and all that!!. why it's unburnt though is the interesting problem if it is indeed two stroke oil?
How about draining the foot oil and running it in neutral to see if it still leaks .

[Juan]

That's a good idea!!.... assuming it's safe to run it with no oil in the foot. I was planning on changing the oil in the foot again anyway.

[985crabs]

Juan, you said this motor was build with a VRO system that was disconnected by the skeptical, non-believer previous owner. The VRO is designed to deliver a much higher concentration of oil at certain RPM levels (low, I do believe) and much less oil at mid-range and higher levels. V=Variable. The mixture can vary from 50:1 to over 100:1 which saves a lot of $$ on $30/gal. 2-stroke oil. Without VRO you're giving it a constant feed of 50:1. Have you run it in the water or is this all just on ears in the yard? If it's all been in the yard then that accumulated oil that would normally be flushed into the pristine environment and piss the owl-huggers off is simply dripping into your Tupperware container.

If it doesn't have that lower unit oil funk to it, which is a funk in and unto itself, and it smells and feels like burned (or partially burned) oil, I'd let it ride. There may be a small breach in the exhaust system, but I think you're okay.

[gnrphil]

Should be fine to run it with no oil in neutral and I agree with crabs, If it's not hurting anything run it like it is. I just like things to be right

[Juan]

No, I haven't run it in the water yet.. I just bought it and I like things "right" too and have been fixing up all the small things that needed fixing on a 1976 model boat and 87 motor.. waiting for it to warm up before launching it in the big water so it's only been run with muffs.
I hope your explanation is right Crabs...I'm 99% sure it's not lower unit oil since there is no smell to it.

[985crabs]

Juan,

I make no representation that I am an outboard mechanic. I'm merely sharing my experience with you. In my layman's opinion, your motor is okay and there's a rational explanation for what you are witnessing. That's a sweet little boat you have there. I'd like to point out that the gunnels are considerably lower than those on your Sea Pro. Given the considerable girth displayed in your profile picture, make sure you don't swamp her if a pirogue goes by!

[Juan]

Careful... you're gonna make someone believe that's really me in that picture! rofl

I'm sure I'll have at least 6" of gunnel above the water line. emthup