oily

[wellman1]

hi all, I have a yamaha 70hp 2 stroke autolube, 1996 and its running well apart from one thing. I noticed when its in the water there are signs of oil coming from it, after putting on the muffs and running the motor, it looks like the oil is mixing with the water coming from the prop as its a milky color. I collected some of the water and let it sit overnight just to see if it was air but it was still white next day. anyone know what can cause this, could it be the head gasket?

[TownsendsFJR1300]

Check your lower unit oil for any water intrusion.

That lower unit is almost 20 years old and seals fail over time, especially if that LU is original.

Please post back what you find...

[wellman1]

I,m not sure how to check out the lower unit. is there an oil drain plug?

[wellman1]

I removed the lower unit oil drain screw and a small amount of oil came out, enough to see that its a normal heavy gear oil with no sign of water mixing with it, plus the fact that it overflowed makes me think that the seal is ok. is it possible that some unburnt 2 stroke oil is getting into the water via the gead gasket or elswhere?

[99yam40]

If a cylinder is not burning the fuel/oil mix properly then it will come out the exhaust through the prop, same place the cooling water comes out.

[TownsendsFJR1300]

Glad you ruled out the LU.

There is a similar flat head screw, higher up in the gear case, (should be the right hand side.)

With the engine level, pull that plug and top off with lower unit oil.

If it looked somewhat dirty or hasn't been changed in a year, it'd be a good time to fully drain and re-fill.

Can you take a pic of that fluid you caught and post it?


More importantly, pull the spark plugs and make sure they all look about the same, tannish.

One not burning, etc will look different from the rest....

[wellman1]

i removed the 3 sparkplugs and the middle ones center electrode is a bit darker colour, could this be low low compression or head gasket?

[wellman1]

the oil that came from the upper vent hole was dark almost black.

[TownsendsFJR1300]

Before you start pulling heads, etc, do a leak down test on all the cylinders. It'd be quite obvious if that cylinder is leaking.

Water entry usually tends to clean the spark plug, not make it blacker. That cylinder may not be firing (worn spark plug) but you state it runs good/normal...

Re the oil, sounds like it needs changing, cheap insurance anyway.. Year old LU oil usually comes out much cleaner than engine oil...

[wellman1]

I had suspicions about the middle cylinder before and switched plugs between cylinders with the result after a good run out the middle plug went a darker colour of brown again, I will try a leakdown test, how exactly is that done?

[wellman1]

I did another test just now, removed low tension feed to the two good cylinders and started the engine on suspect one. the engine started and ran on suspect cylinder, so all I can think is it is either the head gasket or a weak cylinder. would it be safe to continue using the outboard until end of season and maybe overhaul it later?

[TownsendsFJR1300]

This is the leak down tester I use;

https://www.otctools.com/products/cy...age-tester-kit

Its not very expensive and easy to use. (you will need to borrow an air compressor) There's video's there on how to use it on the site.

I wouldn't be in a hurry to tear the engine apart, I would buy, borrow, etc the tool and check it.

I can't answer you question because if it is sucking water it doesn't belong, your making it worse.

If it runs fine, no water intrusion, your probably ok.



**IMO, TEST the basic internal health of the engine before anything else..


BTW, for the test, your basically bringing the cylinder your testing to top dead center and locking up the flywheel(so the engine doesn't turn).

Insert the tool into the spark plug hole, add specified amount of air. The gauge will show how much leakage you have and you can usually hear it if bad enough. If one cylinder is much lower than the others, there's an issue there (bad head gasket, rings, etc)

[wellman1]

oily

I will see what can be set up for the test. in the meantime I will keep using the outtboard as there is no water getting into the cylinders. many thanks for your help.

[zenoahphobic]

I will see what can be set up for the test. in the meantime I will keep using the outtboard as there is no water getting into the cylinders. many thanks for your help.

If engine is running reasonably but a plug gets dark and there appears black oil, then you need to check the oil.
The pump may be on full. Check linkage to it and see if it moves with throttle movement.
Or your oil may be wrong, is it car engine oil or two stroke marine oil for instance?

[wellman1]

I am using ordinary 2 stroke oil in the autolube, but the fact that one cylinder plug is a darker colour is more of a worry. there is no sign of pure oil coming from exhaust, just signs of oil mixing with the cooling water, which makes me suspect head gasket or maybe sticking rings. I will check the linkage to the oil pump later.