[Roundabout]

This protrusion doesn't look factory to me. An idea what it's for?

The green thing is the driveshaft.

 

[Harix]

It's factory. Coolant drain before storage (in frozen temp).

 

[komiko]

Instant hot water?

 

[cain-it]

Bob its the engine block coolant drain plug.
If you flush / drain / replace the coolant you'd need to open this too to ensure as much as possible is changed to fresh

 

[Roundabout]

OK Thanks!

 

[enderw88]

I love that! You can put a hose on it and not spray coolant all over the place. Every block drain I have seen for the last twenty years was just a hole straight out the side.

 

[Roundabout]

And if you run straight water, you can make hot cocoa and instant coffee on blustery track days as komiko suggested. Sounds like the basis for an April Fools post...