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2 stroke oil leak

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Southpaw84

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1D9DBA89-8455-4AD1-AFCB-FEE3AF19A5ED.jpgA8C95143-2CB7-42E3-8F55-D8050DBC7420.jpgI Hi everyone, new to the forum and kind of new to boating also.
I recently had a 1990 yamaha 90hp 2 stroke installed on a bass boat, the motor runs great but I noticed some slicks behind the boat while trolling the other day. When I got home I realized that it was leaking some 2 stroke oil but not from the cap or the tank. I can’t figure out where it is coming from. I can only see where it is exiting, which is down the leg on the inside towards the boat. Also when I have it tilted up on the transom saver it comes out on the same side but right where the lower unit bolts to the leg. I’m not sure if it has anything to do with it but the mechanic I boat the motor from is who also installed it and he told me to add about a quart of oil to the tank when I fill it which seems weird since it is oil injected. Any help is appreciated
 
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Oil stored in the oil reservoir is mechanically driven into the manifold. Oil is not delivered anywhere else. So you either have a leak coming from the tank or one or more of the hoses delivering oil to the manifold.

The other causes could be a faulty oil check valve or the oil pump is not metered to spec, either of which causes excess oil to enter the manifold. When the engine is off and tilted up, normally the back pressure in the oil hose is held in check by the check valves. If a check valve is bad any pressure in the hose will cause oil to flow into manifold, excess oil. Depending on the tilt angle of engine, this excess oil flows out of carb throat and drips down into lower cowling, lower cowling into mid section and out where you've witnessed.

To figure out where the cause of the leak/unchecked flow of oil, I'd first refer to your service manual on how to verify the oil pump is to spec. Then give a good cleaning/wipe down to oil tank, hoses, manifold. Run engine to normal operating temp, then maybe a few minutes more. Shut down, tilt engine up and watch for leaking oil. If you have a silencer over carbs, remove it before tilting engine up so you can see the carb throats. If you see oil dripping out of throat, one of the oil check valves is bad.
 
Would this also cause it to leak while the motor is running and not tilted up? If I don’t tilt the motor and run it on earmuffs it leaks oil out right where you can see in the pictures
 
Southpaw84 said:
Would this also cause it to leak while the motor is running and not tilted up? If I don’t tilt the motor and run it on earmuffs it leaks oil out right where you can see in the pictures
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Not sure what "this" is that you're referring to. If the cause of the oil leak is from that which contains the oil (reservoir, hoses), then it wouldn't matter the tilt angle of engine or whether it's on or off, it will just continue to leak from xyz.

Is the bottom of the pan (lower cowling) covered with oil? When the mechanic/previous owner told you to add extra oil to reservoir, did you ask why?
 
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I’m sorry, I thought I sent this through the other night...what I meant by “this” was a bad check valve(s). I don’t really see a lot of pooling up in the lower cowling. And I did ask the mechanic because it seemed odd and he told me it was because the motor is older and with the ethanol fuel around now the engine needs it. I didn’t question it at first too much because he says a 20 year yamaha tech
 
Southpaw84 said:
And I did ask the mechanic because it seemed odd and he told me it was because the motor is older and with the ethanol fuel around now the engine needs it.
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Yes, a bad check valve will cause oil to leak out of the contained oil/fuel system.

Let's just say your mechanic's theory of the engine's age being the reason it requires more oil than Yamaha recommends, and because more oil has been added, this is the reason the engine is leaking oil. My question is, would this extra oil to fuel ratio result in oil leaking OUT of the oil/fuel system and onto the outer shell of mid section? I guess what I'm saying is you could add oil at a ratio of 10:1 and you still shouldn't see oil outside of the oil/fuel system...a dark smokey exhaust, yeah sure.

The theory of adding extra oil to the fuel for 2 strokes is just that, a theory. But it's one I understand, and I don't believe adding a little extra oil to these older engines could hurt at all. Be that as it may, adding the extra oil shouldn't result in an oil leak. Something to think about.
 
ClassicAQ said:
Yes, a bad check valve will cause oil to leak out of the contained oil/fuel system.

Let's just say your mechanic's theory of the engine's age being the reason it requires more oil than Yamaha recommends, and because more oil has been added, this is the reason the engine is leaking oil. My question is, would this extra oil to fuel ratio result in oil leaking OUT of the oil/fuel system and onto the outer shell of mid section? I guess what I'm saying is you could add oil at a ratio of 10:1 and you still shouldn't see oil outside of the oil/fuel system...a dark smokey exhaust, yeah sure.

The theory of adding extra oil to the fuel for 2 strokes is just that, a theory. But it's one I understand, and I don't believe adding a little extra oil to these older engines could hurt at all. Be that as it may, adding the extra oil shouldn't result in an oil leak. Something to think about.
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Yeah I understand what you are saying, I’m just trying to cover all bases at this point. I’m going to put new clamps on any of the hoses coming from and going to the oil tank and probably replace the three check valves. Then I’ll go from there. Thank you for your help
 
I have an 87 Johnson 150 V6 vro removed so I'm mixing gas in the tank. Went to a river system yesterday a d it was idle speed only. When I got up today, I noticed my transom saver was covered in black goo that was running down the back just like yours! I can see maybe it's coming from the bottom of the power drive where it bolts to the cowling? Either way not sure what's up. New to boating here. Some say it's just excessive oil not being burnt due to the idle speed for hours and just needs a good sea foam shock. Any help would be great
 
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