Outboard oil tank question - I think I figured it out.

[Nipfisher]

I have found an issue with the oil tank under the cowling of my 1991 Yamaha 90hp outboard. When the cowling gets warm in the sun the tank expands and pushes oil out of somewhere? It pools in the bottom of the engine compartment then leaks down the motor to the foot. I have checked all the hoses and clamps. I removed the tank and it is not leaking.

 

 

My question is ............ can I put a breather hole in the top of of the cap? Will it screw with the oil injection?

 

 

Any other suggestions? I know there are several mechanically inclined members on this board.

 

 

 

 

Turns out that the cap has a breather on it but that the inside piece of the cap was rotated the wrong way not allowing the air to pass through the breather holes.

Edited May 7, 2013 by Nipfisher

[HTHM]

I have an Optimax, and sometimes have the same problem, it was cured by replacing the small cap on the oil tank. My understanding is that the oil system is under pressure, so a vent may not be the best solution.

[DRIFTER_016]

Have you changed your oil lines yet?

The lines on the tank of my 1991 Merc 90 hardened up and over the winter one failed and actually fell off (thankfully not while I was running down the lake).

I came out to find oil all over the place and my tank empty.

[Nipfisher]

Have you changed your oil lines yet?

The lines on the tank of my 1991 Merc 90 hardened up and over the winter one failed and actually fell off (thankfully not while I was running down the lake).

I came out to find oil all over the place and my tank empty.

 

Dave, I have checked all the lines and they are still flexible. All the clamps are tight and this is a SLOW leak. Over the spring (last 2 months) I lost about half of my tank. It was 3/4 full and is now just above the minimum line.

 

Where would I buy the oil lines? They are black in some areas (normally clear) .

[Nipfisher]

I have an Optimax, and sometimes have the same problem, it was cured by replacing the small cap on the oil tank. My understanding is that the oil system is under pressure, so a vent may not be the best solution.

 

There is a rubber cap on top for filling the tank and there is another smaller cap but it has the sending unit in it.

I will post some pictures tomorrow night.

[Nipfisher]

I cleaned up as much of the oil as I could. I put the cap back on and the cowling. It will sit in the sun tomorrow and I will check to see it it is still leaking.

[DRIFTER_016]

I just bought fuel line @ Napa to replace the original lines.

The leak could be at the fitting that goes into the bottom of the tank. It could also be where the oil level sender mounts or it could have a split on the seam of the tank it's self.