Through-Flow ventilation

In fact, those vents at the back of the rear side windows on later
(1986-1992) Caravelles and Vanagons are not "exhaust vents" but ENTRY points
for fresh air.

In the early days of steamships it was discovered that, when a ship was
under way, air inside the hull flowed from the stern to the bow.  Similarly,
for moving motor vehicles, air always flows from the back to the front and
this is the basic principle upon which all vehicle through-flow systems
work.  Even the little slotted aperture at the base of the front doors on
later T2 (bay-windows) and all T3 (Caravelles, Vanagons, etc) takes in air
from the cab interior and sends it through the door to the front of the door
where it is expelled through the slot between the door and the A-pillar.

So, the best way to achieve a through-flow of fresh air through a Vanagon or
Caravelle is t0 have a rear-most side window open.

However, if one makes the window at the rear door or hatch openable (as
suggested with a safari rear window), one would be courting disaster.  Air
contaminated by the vehicle's exhaust would be sucked in.  The occupants
would soon develop headaches, fall asleep and die from carbon monoxide
poisoning if they didn't first get wrapped around a tree when the driver
dozed off.

Simon Glen
Toowoomba, Australia
1992 syncro van