What's the name of that piece of plastic in the valve cover and what does it do?

[92EcoDiesel Jetta]

The only thing I can think of is it keeps oil from splashing out of the oil filler cap when the engine is running.

Makes it difficult to put a funnel in there when I have to add oil. What happens if I take that plastic piece out?

[bajacalal]

It's an oil baffle (don't know the official VW name for it) and it keeps oil from being drawn into your crankcase ventilation system, which causes engine runaway on a diesel engine! It is considered an upgrade/improvement over engines that were not equipped with it so while it is annoying when adding oil, I would leave it in or at least sell it to another member. Don't throw it away. You could maybe put a small, funnel sized hole in it.

[maxfax]

You could maybe put a small, funnel sized hole in it.

That right there is flat out a damned brilliant idea...... 

[ToddA1]

I've done that on the last few that I've installed.  A Unibit makes a nice, clean hole. 

I make it large enough to fit an oil container spout, in there.

-Todd

[92EcoDiesel Jetta]

I wonder how well it works in practice to prevent a runaway. It does not form a perfect seal and the oil fumes can still get out of the VC vent into the turbo.

[8v-of-fury]

but it does stop the full on globs of oil that fling off the cam lobes. It doesnt stop the oil getting out of the top of the engine by the cause of blow-by.. but it significantly decreases it.

[maxfax]

I wonder how well it works in practice to prevent a runaway. It does not form a perfect seal and the oil fumes can still get out of the VC vent into the turbo.

The oil fumes have to get out, or you'd be popping seals all over the place.. As Jeremy said, it stops full glob of oil from being slung in the breather at high rpms..  Even helps the V/C gasket to leak less if you're still running cork...

I'm still boggled over the hole in the baffle for filling the engine with oil.. Dunno why I didn't think of that.. Of course I haven't changed oil in my car in well over a year, and rarely bother to add any..