Heres a picture of the gizmo I made to test the pressure cap.
https://picasaweb.google.com/101787477383733954114/Vanagon  Cheap Harbor
Freight adjuster/gauge assy coupled to a pvc fitting. (had to turn down the
pvc to fit inside the cap). Clamped the gizmo to the cap with some vice
grips and connected to air compressor, let air in via the adjuster untill
it bled off. Easier to tell when it bleeds off if you connect a hose to the
cap and stick it in some water, watch for bubbles. As I mentioned earlier,
caused me NOT  to use a new cap I had just bought because it didn't open
untill 40#'s