Outboard Oil System

[Interim]

I have a yamaha F9.9 (late 1990s model). When I drained the oil, it came out a bit too fast for oil, and overflowed my quart cup (I think the capacity is a liter, so it should overflow a little, but this perhaps a cup full too much).

The oil didn't have any water in it, so I am wondering if I could have fuel in the oil. My paranoia makes me think it smelled a little like gas, but not definitely. Is it possible to get fuel into the oil system?

When the boat is in the slip, I tilt it to get the prop and water intake out of the lake. Maybe it's at a 45 degree angle or a bit more.

Any thoughts would be appreciated.

--john

[grady]

Yes you can get fuel in it if the carburetor needle valve is leaking.
Could just be old oil. When was the last oil change?
If it is fuel you should replace the carb gaskets, seals, needle valve, and possibly float.

If it is the same as mine T9.9 1994.

[Interim]

I changed the oil in the Spring before put-in, and ran it all summer. It came out very clean, but not quite as clean as new oil.

Is there a good way to check the needle valve, or is this one of those "if you check it, just replace it" jobs?

--john

[grady]

I changed the oil in the Spring before put-in, and ran it all summer. It came out very clean, but not quite as clean as new oil.

Is there a good way to check the needle valve, or is this one of those "if you check it, just replace it" jobs?

--john

Pull the cowl off and look, smell inside the intake. After a day if it smells of gas or you can see vapor get the carb rebuilt. Pay someone of you are not good at mechanics it will save you money in the long run.

[ULLR]

Agree..probably fuel in oil. Will usually evaporate when it gets hot and runs but no so good for the bearings in the meantime. It is also a good practice to note oil level when it is changed and evertime it is used as oil level should either stay close to same or lower as it gets older. Anytime oil level increases it indicates there is another fluid getting mixed into it....good news is fuel is better to have in it than water!

[grady]

good news is fuel is better to have in it than water!

Yes, at one time it was comon practice to dump fuel in the oil tank of aircraft engines at shut down so you could start them later in the cold.

[ULLR]

good news is fuel is better to have in it than water!

Yes, at one time it was comon practice to dump fuel in the oil tank of aircraft engines at shut down so you could start them later in the cold.

Funny you mention that....must be a fellow pilot, I was going to mention the same.

[Interim]

That might explain why it starts so easy

My experience is with car engines, and have never looked for increasing oil levels before. Something to watch for.

Not only do I have fuel in the oil, but I have some oil around the intake. I guess this, and a bit of smoke in the exhaust, are because of blow-by. Do I worry about piston rings, or is this more likely the result of titling the engine when it is docked? I would always leave it tilted straight, but a couple times it would be on one side or the other the next time I was there. I know there is a sticker indicating the three ok and two not OK sides to lay it on... perhaps it went the wrong way once and fuel flowed into the carb and down the crankcase vent. Just a theory.

I'll try the carb rebuild this winter. I've done a zenith stromberg on my MG before, so I'm hoping yamaha is within my skill range.

--john

[BillOcala]

This happened to me with my 2010 9.9 Prokicker with only about 60 hours on it. The culprit? My fuel tank was in the hot sun and the vents were all closed. The tank for some days was swelling up like a balloon it was under such pressure. This forced fuel past the rings. (I now disconnect the fuel tank when not in use - and I always provide for pressure to have somewhere ELSE to release!.

[Interim]

Another good tip. My tank is sealed, but I could see those ball-bearings giving way. Easy enough to pull the line off at the motor.

Am I right about the path? Fuel in the carb can get into a crankcase vent hose? Or is there another pathway?

--john

[ULLR]

I would try the carb kit first....cheep and easy. If you have lots of blowby from rings you usually get blue smoke that doesn't go away even once it is warmed up. Simple check for blow by is to do a compression test...for the time it takes it may be worth it. High blowby usually makes the engine harder to start, not easier though....