Looks like synlubes beat me to it. Anyway this is what I posted :
Afraid not, air will actually go into engine bay from the wiper motor area, depending on how fast the car is going. This is because when the car travels at speed, a high pressure area forms at the base of the windshield.
There used to be a great article called "early Z aerodynamics" I tried to search on google hoping to find a link but it is gone.
here's part of it :
"....The high pressure continues all the way to the windshield at station 60, which is why ventilation air intakes are located just in front of the windshield, and also why opening the hood slightly does not result in significant venting of hot air from the engine bay. One would think that such a large area of high pressure would push the hood and windshield down, but lift generated by the air dammed up by the front of the car is greater and the net vector is upward....."