The vent is actually a heat extractor. When sitting still you will see some heat escaping through the vent, but when the car is in motion the vent design creates a low pressure area which actually helps suck air out from under the hood.
Did the vents come with the lower plastic flap attached? Personally I removed the plastic rain flap because it allows for more heat to escape the engine compartment. Then again I don't ever drive my car in the rain so it's not a problem for me.
Even if the rain flaps are left in the stock position rain can still enter the engine compartment, in fact on a stock 03/04 with the flaps in their stock configuration rain actually gets channeled between the hood blanket and the bottom of the hood and eventually discolors the hood blanket.
When the flaps are removed or pinned back the majority of rain or car wash water drips straight through the vent between the radiator & motor. Some does hit the coolant reservoir.
U.M.
