Oil filler neck vent lines and check valve on RX DI

[statikuz]

On the oil tank filler necks of my two RX DIs there is a small semi-circular plastic piece that has a tiny piece of hose and a little check valve that clips into the bottom edge of the filler neck.

Picture from the bottom:

Connected to the neck are two lines, one that goes to the bottom of the crankcase right under the air compressor (oil return line?) and another that goes to the PTO side throttle body (vacuum line?) Does that seem right?

Basically I want to understand why this little check valve is there, and if I can do without it as both of mine are broken and it's not sold separately from the filler neck ($30).

I read this thread:

XP DI oil tank vent system

... which said his example was broken (but both of mine look exactly like that too). I would kinda understand if the bottom of the oil neck was sealed all the way around, with this check valve being the only outlet and allowing air and oil return into the tank but that's not the case as it's missing a whole third.

To me it seems like it's pointless altogether. Or does that plastic piece just exist to prevent oil from going down either of those vent lines when you add oil via the filler?

Here's some eBay photos that show one without the nipple/check valve altogether (like the above post).

 

[mikidymac]

Seadoo put it there for a reason so I would replace it.
Also the check valve has been known to fall to the bottom of the tank and plug the oil to the engines.

 

[statikuz]

Yes, I read all of that in the other thread but why is it there? I can't see how it serves any purpose at all. That's what I'm trying to figure out.

 

[statikuz]

So, for anyone else that comes upon this, I stumbled across an explanation that makes a bit more sense on a defunct Seadoo website.

Sea-Doo.net - the official website for the Sea-Doo watercraft enthusiast

DI's incorporate a small system that may not be well understood. If the air compressor lubrication system is not functioning correctly, you may encounter smoking, fresh clean oil in the PTO throttle body, clean oil spattered on the back of the boat, and sometimes poor top speed.

The oil pump delivers the same amount of oil to the two cylinders, as the air compressor. Naturally the air compressor does not need as much oil so it returns the used, but still clean oil to the oil tank via air pressure that blows-by the compressor rings. The oil tank filler neck separates the oil from the air. The oil drops down through a one-way check valve back into the tank. The air vents back to the PTO throttle body. If the check valve is plugged, broken, or installed backwards, oil and air pressure is delivered to the throttle body and injects into the intake air. This air pressure and oil can cause running problems, smoke, fouled plugs and raw oil droplets on the back of the boat.

 

[statikuz]

I have even more info now! The dealer provided me this info from the 2002 update book. It hasn't entirely solved my problem because I see in the last photo that the whole circle is intact while on mine it's cut off and I haven't figured out why that is so.