Yanmar 2GM20F vent tubes

[Cmusicbear1]

My 1986 2GM20F has, on the starboard side, two transparent, or so they used to be, vent tubes hanging down almost to the engine bilge. One is for draining the cooling system I suppose. I cannot physically see the origin of the other. I can however see the black oil discharging from it into the bilge. I assume this is engine oil however it does seem quite thin in it's consistency. My general question is: From where is this liquid venting and possibly why? This is a recent development.

Cliff P.
Zephyr
1986 Hunter31

[speciald]

Interesting question. The engine diagram showsonly one tube on that side - for coolant drainage. The only other clear tube runs to the coolant reservoir to the overflow by the radiator cap.