Something I have often noticed but thought nothing of, as the car was always off when observing this....but the view behind the twin kidneys on my 520D ED always seems to present a closed-vent, you know those black horizontally arranged blind-style slats?
So last night when the car had been a lengthy enough run, when I parked up I left her running and popped out front to check, peered in through the kidney grills and was fully expecting them to be open as it was a hot engine, and was still running as stated, and the internal air conditioning was not set to the recycle mode (the one that prevents air from outside entering). The slat were still closed? Surely that's not right, or good? Can anyone confirm their observations on their own cars?
Edit: An interesting nugget found on other site...and not at all in an annoying monotone voice ...
And from another forum someone posted an extract from a BMW blog as follows:
"The air vent control reduces aerodynamic drag.
An Efficient Dynamics stratagem deployed at an early stage in a number of different models is air vent control. Air intakes to feed cool air into the vehicle always degrade the aerodynamics of that vehicle. The air vent control system compensates for this disadvantage by the use of movable slats, located between the air intake and the radiator. When the engine and its ancillary systems require a low level of cooling, the air vents close. Thanks to the improved vehicle aerodynamics resulting from this action, fuel consumption is reduced and unwanted external noise is minimised.
The new, second-generation air vent control system is variable.
Back in 2003, air vents were already being used behind the kidney-shaped grille on BMW 5 Series vehicles. Ever since 2007, the first generation air vent control system has been fitted to a number of different BMW models. Three different vent positions can be set using the three upper and two lower slats which are connected together, depending on the engine fitted to the vehicle. With the second-generation air vent control system, a much greater number of positions can be set in order to better control the flow of cooling air in an even more flexible, demand-led manner. Now, both the upper and lower slats are opened or closed to precisely-defined positions by an electric motor. The second-generation air vent control system also incorporates more perceptive sensing technology, which captures and evaluates more parameters than ever before. In this way, the temperature of the refrigerant, the air conditioning condenser, the transmission oil, the catalytic converter and the charge air feeding the turbocharger all benefit. Another important control variable is the speed at which the vehicle is driven.
Clearly linked to driving situation.
After pulling away at the start of a journey while in town, all of the slats remain closed to allow the engine and its ancillary systems to reach optimal operating temperature as quickly as possible. Once a greater degree of cooling is required, the lower slats open first, moving by an angle of 30 degrees. On the open road, the aerodynamics of the vehicle already play a major role. At low load, the air vents are gradually closed in a number of intermediate steps; during this process, the lower slats can also be opened, by 15 degrees only. On the motorway under full load and at high temperatures, a situation that demands maximum cooling performance, the lower slats can be opened completely, as can the upper slats to supplement them. The positioning of the slats in a number of discrete steps, in which the upper slats always open last and are always the first to close, is particularly important. Because when closed, the upper slats make the greatest contribution to reducing aerodynamic drag. Overall, the second-generation air vent control system reduces the drag coefficient cW by 0.015."