Do the deck lid grilles on the 1972 Beetle suck in cool air or let hot air out ? I always thought VW added them to let in more cool air to the engine but someone told me the hot air from the engine compartment is exhausted through the deck lid stock vents ? Seems to me they only bring in more cool air for the larger engines and larger cooling fan ? What is the air flow going to them, either it sucks in or exhaust hot air ? What is the verdict on this ? Thanks.
As Mikko K said above, the vents help to get more cool air into the engine bay for the fan to suck it in and blow it out below the engine (and through the heat exchangers if you have a stock exhaust system.
That's the reason why cabrios had them in the engine lids first. They have no air vents below the rear window so need to get the air from somewhere.