Beating a dead horse- the oil cooler flap set-up sounds identical to the 
Vanagon - it is so incredibly dumb -that I still cannot believe I have 
installed it properly (although Haynes and your description make me 
believe that I have).  Though I still don't understand how  the fan air 
finds it way back to the cooler when it is being vented out and 
downwards. How can wind travel against itself? And why the lip seal all 
around the cooler top?

I had another theory though on how it is suppose to 
function - since the bottom portion of the oil cooler is open  to the 
elements and is in the direct path of hot air being vented out past the 
cylinders, this may create a low vacuum area as the hot air rushes past 
the oil cooler fins and out the back. This low pressure area in turn 
pulls cooler air from above thus "cooling the oil" however feeble that 
may be. Maybe a scoop could be created so as to vent some air back into 
cooler?

To return to an earlier point made, given that your bus and my Vanagon 
employ the same cooling system on very similar engines, doesn't it strike 
you as odd that the oil cooler is expected to do the same job on a vehicle 
that is substantially larger, broader and heavier (more if it is a 
Westfalia).

BTW in my mini-poll for ac Vanagons (only 8 responses) no one knew their 
oil pressure - ignorance is bliss. More on this later if and when I get 
more responses - DC