Jeez...

I had no idea my scoops would get everyone's knickers in a twist.  As I (apparently unsucessfully) tried to tell G. Mathew I've already had a bit of "seat of the pants" testing of scoop/no scoop testing on my turbo diesel.  Without scoop and with a fairly substantial flat oil cooler mounted horizontally in the tunnel I've created behind the passenger side rear wheel well by cutting a 10" x 10" hole in the existing horizontal sheet metal and partitioning off the area from the engine compartment with more sheet metal...the engine oil runs about 220 degrees at 70mph with ambient air temperature of about 80 degrees.  With an earlier version of the scoop the temperature dropped to about 200 degrees. SO THERE!
As far as any nonsense about the existing vents being there to exit hot air instead of inlets, then why would VW clearly make them pointed toward the front of the van.  At best one could argue they are there for exiting hot air when the van is stopped and idling.
But look...let's be honest for all of VW's supposed engineering prowess they've made a few mistakes as well.
When I get the finished scoops back from the fiberglass guy in a couple of days, I'll mount one and let you know how it works.  Maybe I could attach a couple of ribbons of varying lengths to the back window and see which way the wind blows too....nah.
 
Mark Thoma